Case For Moon First

Gateway to Entire Solar System - Open Ended Exploration, Planetary Protection at its Heart

Copyright © Robert Walker

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Cover picture shows the famous Earthrise photograph taken by Apollo 8, the first mission to orbit the Moon, on Christmas eve, 1968, together with a detail from the 1965 Russian film Luna).

First Publishing on Kindle: April 2016

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Main sections - and skip to detailed contents

The main sections of this book are:

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Preface = why go to the Moon first?

(skip to contents) (Links in the text in this preface take you to other sections of this book)

You may have heard advocates say we should ignore the Moon, and head straight for Mars, and they may even say that the Moon is as dull as a ball of concrete. But what about the other view, put forward by many enthusiasts for the Moon, that we should start there instead,as the first place to send humans after LEO? As you read this book, you may be surprised to learn that the Moon is resource rich, and fascinating, with many new discoveries since the time of Apollo, as well as many mysteries still to solve. It may have potential for exports of metals and volatiles. It's also far more promising for tourist hotels, and human research stations, because it is so much easier to get to than Mars, it's a great place for radio and infrared telescopes, and it's potentially valuable as a place to make computer chips and solar cells that require high vacuum, amongst other benefits. And it may surprise you a lot to learn that the Moon has many advantages over Mars as a place to create habitats for humans too.

Inside look at one of the ideas for the ESA moon village, using 3D printing on the Moon for the radiation shielding. Image credit Foster + Partners / ESA. Their new director, Professor Johann-Dietrich Woerner is keen on taking us back to the Moon first, and has an exciting vision for a lunar village on the Moon as a multinational venture involving astronauts, Russian cosmonauts, maybe even Chinese taikonauts, and private space as well.

That's actually the plan of the ESA, India, Japan, China etc, they all want to send humans back to the Moon first. Many US astronauts and space enthusiasts think the same way, but their voice doesn't get heard so much in the States. Even Buzz Aldrin, a keen Mars colonization advocate, didn't entirely agree with the way Obama quoted his "Been there and done that" saying he meant it facetiously.

You need to look at the Moon with "Moon spectacles" and when you do, in one comparison after another, the Moon comes out top. It's also close enough to scout out with robots controlled in near to real time from Earth. Then once we decide on a site for our base, we can use them again to get our lunar village ready, with the habitats, utilities, landing beacon and landing pad all in place, before our first astronauts arrive.

The Apollo astronauts were like the early Antarctic explorers, who set their first footprints on an almost entirely unexplored territory, this time in space. Though none of them died in space or on the Moon, their missions were risky and new missions back to the Moon will be also.

Nevertheless, the Moon is a far safer destination than Mars. We know we can do it, and we can set off at any time, with lifeboats to get us back to Earth within three days in an emergency. A mission to Mars would be a multi-year journey with no lifeboats. An Apollo 13 type accident could not be survived, and a mistake which just leads to the crew abandoning their base on the Moon would kill everyone at the distance of Mars. This also makes the Moon a place where we can try much more adventurous ideas and experiments with methods of living there.

Shackleton's Endurance trapped in the ice in Antarctica before it sunk. Shackleton's part overwintered huddled beneath boats and hunting seals for food. Antarctica is far more habitable than Mars, and back then, before the Antarctic treaty, the whole continent was open for colonization, if anyone had been interested, but there were no efforts by any nation to colonize Antarctica. We don't colonize all the possible places where humans could survive.

The enthusiasts for Mars colonization present a rosy picture of a colonized Mars and they think that we will succeed in colonizing their favourite planet, so long as we start on it quickly. But there are many places on Earth that we don't colonize. Indeed, to date, we have only tried to colonize places where humans can survive with stone age technology. What's more, many colonization attempts even of those places have failed.

To go to space to colonize, right now, is like Shackleton saying "Great, we have overwintered on Antarctica, hunting seals and huddling under boats, we must be ready to colonize it!".

Let's go to space like the early Antarctic explorers instead, to find out what's there. Along the way we can discover if there is anywhere to set up home, and we don't know in advance that Mars is that place. For instance, perhaps we may find vast lunar caves, kilometers wide and over 100 kilometers in length, as the Grail data suggests, as vast as an O'Neil Cylinder. If so, these could be amongst the easiest and safest places to build habitats in space. Or perhaps habitats at the lunar poles are best, because of the volatiles we know are there, or as a more out there proposal, the idea of Venus cloud colonies may have more to recommend it than you think. Then there's the 1970s idea of living in large slowly spinning habitats built with materials from the Moon and the asteroids.

Another reason given to head off to Mars as quickly as possible is to "backup Earth". But what plausible near future disaster could end up with an Earth less habitable than Mars, with its perchlorate laced dust storms, solar storms of deadly radiation, half the sunlight of Earth, all fresh water frozen into ice like Antarctica, no oxygen to breathe, and the air so thin that the moisture lining your lungs would boil, without a full body pressurized spacesuit?

If we ever need to restore anywhere with a backup of seeds, technology, and knowledge, it's Earth that we'd restore, not Mars. That makes the Earth itself, or the Moon, the ideal places to keep these repositories.

And if we do send humans to Mars, why not study it telerobotically from its moons or from orbit first, in a shirt sleeves environment? Why rush to the surface as quickly as possible, and risk a human crash in the one place in the inner solar system most vulnerable to Earth microbes? I would be the worst possible anti-climax in the search for life in our solar system to get there only to discover life that we brought ourselves.

In this vision, human space exploration is open ended. We have the entire solar system to explore with our missions, from Mercury all the way out to Jupiter's moons and beyond. The Moon is our gateway and natural starting point for this exploration. And there's no rush; we can afford to keep our future options open as we explore and find out what the possibilities are.

You can hear me talk about this book and answer questions about it as guest for David Livingston's TheSpaceShow in his Broadcast 2710: Robert Walker

This book is also available on kindle

Contents

EXECUTIVE SUMMARY

Skip to contents list. (Most of the links in this section take you to appropriate sections of this booklet)

If you prefer to listen to it, here I am reading out the executive summary:



(click to watch on Youtube)

The Moon is our nearest unexplored territory outside Earth. To ignore it is like ignoring Antarctica after the first few landings in the nineteenth century. Why rush humans as quickly as possible to distant Mars, the one place in the inner solar system most vulnerable to Earth microbes?

The Moon in this vision is a gateway to the solar system, a place to develop new techniques and explore a celestial body that is proving much more interesting than expected. Along the way, we are bound to get human outposts in space, and colonization may happen also.

However, settlement in space doesn't need to be the driving force, any more than it is the driving force behind the study and exploration of Antarctica. If we try to turn Mars and other places in space into the closest possible imitations of Earth as quickly as possible, this may close off other futures, like the discovery of vulnerable early life on Mars, or better future ways to transform Mars.

Once we develop the ability to live in space for years at a time, the whole solar system will open out to us. While keeping future options open on Mars we can explore Venus, Mercury, asteroids, Jupiter's Callisto and further afield, and Mars itself via telepresence. We also have many experiments in human settlement to try closer to hand on the Moon. This can be an exciting future, with humans working together with robots for remote exploration, as our mobile sense organs and hands in the solar system and galaxy.

SEARCH FOR INSPIRATION

If you are keen on Mars colonization, it is not hard to find a future vision to inspire you. Elon Musk has plans to send a hundred people at a time in his proposed "Mars Colonial Transporter" and to found a city of 80,000, and eventually a million. He is due to reveal these plans at the IAC conference this September. And NASA, though they don't have such a large scale vision, aim to land human boots on Mars, with an eye to permanent Mars settlement in the future. You can also join the Mars society and read the books of Robert Zubrin.

But what if you are keen on humans in space, but don't think we have any realistic chance of colonizing the planet? What if you love science, and think "boots on Mars" has significant planetary protection issues? What can your future vision be? You have to go back perhaps to O'Neil's "Colonies in Space" vision of the 1970s to find an alternative that has the same level of positive inspiration as this Mars colonization idea.

This book presents a gradually evolving alternative that I think can be a positive future inspiration, based on the Moon as our next place to visit and start permanent settlement rather than Mars. Although it builds on the detailed plans of "Moon firsters", such as Paul Spudis, Dennis Wingo, Madhu Thangavelu and David Schrunk, this vision is perhaps more open ended, with new goals that we discover along the way, and has planetary protection as a core principle, indeed as one of the many reasons for focusing on the Moon before Mars, and Mars exploration from orbit before we consider sending humans to the surface.

WHO THIS IS FOR

Are you keen on humans in space, but think Mars could be a step too far right now? Do you think we are bound to need to support our space settlements from Earth for a fair while into the future, just as we do for inhospitable places such as Antarctica? Do you think our exploration should be open ended with science as a core objective, and planetary protection and reversible biological exploration as core principles?

Do you see the Moon as an exciting first place to visit and explore, and see robots as our mobile sense organs in the solar system? Do you think that it's not quite yet the right time to relax planetary protection guidelines, and don't want to make Mars more vulnerable to Earth life?

Then this may be a vision for you. And if not, well I think you may still find much here of interest and perhaps may get many surprises.

LUNAR VILLAGE

This is the ESA video about ideas for small robotic missions first, followed by Antarctic base type settlements on the peaks of (almost) eternal light at the lunar poles.



(click to watch on Youtube)

I use ESA as my main example here and throughout this book, because they seem to have the most developed ideas for a Moon base of any of the space agencies currently. What's more, they are actively pursuing their idea of a moon village, with a reasonable chance of success, since it's based on many established international partnerships.

That includes their partnership with Russia. Then, though currently NASA say that they won't send any astronauts to the lunar surface, they are open to partnerships in other ways. ESA are already committed to partner with the US in their Exploration Mission 1 / 2 to enter a distant retrograde orbit around the Moon, and they can also partner with India, Japan, and even China, which I think adds to their chances of success.

They are also open to partnership with commercial space and private ventures as well as government space agencies. Of course we could get many surprises in the future, for instance who can tell whether the next president of the US might change direction again and decide to go "back to the Moon", but on the basis of the situation as of writing this, I'd bet on ESA as the most likely to set up a Moon colony, if I was a betting man.

This is the ESA director general Jan Woerner talking about his ideas.



(click to watch on Youtube)

This is their plan for the base itself

(more background)

And this is how they would build the base with 3D printers on the Moon



(click to watch on Youtube)

Adding regolith shielding to one of the habitats (using robots controlled telerobotically from Earth). Photograph ESA / Foster + Partners.

For techy details see: Lunar Outpost Design, 3D printing regolith as a construction technique for environmental shielding on the moon

For more about the advantages of this village idea, see also the section below: How an international lunar village saves money, and is safer than separate bases spread out over the Moon, through use of communal resources

In the process we will find out what humans do best, and what robots do best, starting off with robots first, and then humans on the Moon. Then we can continue outwards in an open fashion, building on what we've learnt.

Meanwhile, we continue to explore Mars robotically from Earth, as well as many other interesting places in our solar system, including Venus, Mercury, Europa, Enceladus, Titan, comets, asteroids and so on. Later, once we have the capability, we can send humans to explore Mars telerobotically, perhaps first though "free return" flyby missions, then from orbit, then perhaps explore Mars from bases on its two moons Phobos and Deimos, and explore its moons themselves. These would be only some of many future human based missions, eventually spanning the entire solar system.

In this approach, science and planetary protection is central. Space settlement happens because you are there for a purpose. As with the Antarctic bases - once we are there with good science as the motivation, it would naturally become a permanent outpost and a first step into space.

Missions motivated by science continue to grow, and engage the public. There is no suggestion that we should stop exploring Antarctica because of the cost of doing science there. What's more, scientifically motivated missions can have overwhelmingly positive outcomes too, especially if we make new discoveries about biology and evolution.

However it's not enough to just say this. We need to try to provide a much more detailed vision. It needs to address the idea that Mars is the obvious next place to go, and somehow provide an alternative vision that is as compelling as that to the human imagination. That's quite a tough task.

SCEPTICISM ABOUT A VIABLE COLONY IN A COLD DESERT WITH A NEAR VACUUM FOR AN "ATMOSPHERE"

If you don't think we have a realistic chance of colonizing Mars, you can present your reasons for skepticism to colonization enthusiasts. You can say that it is sure to be much harder to live on Mars than to set up home in Antarctica, the Atacama desert, or the top of Mount Everest. You can point out that Mars is currently far more like the Moon than it is like Earth in terms of habitability, with its laboratory vacuum for an atmosphere (similar to Earth's atmosphere at 30 kilometers upwards), hard radiation, and extremes of cold.

You can mention that (though it can get warm in the daytime), it gets so cold at night that carbon dioxide freezes out in dry ice / water ice frosts for 200 nights of the year even at the equator. You can point to the additional issues of the global dust storms that can sometimes blank out the sun for weeks on end, and harmful perchlorates in the dust.

I think everyone agrees with all those points. The difference is that prospective colonists see them all as challenges to be overcome, rather than as reasons not to colonize the place. They will point you in the direction of Robert Zubrin's books explaining how it would be done.

You can go on to ask, would that really work as a place where a million people, or even a thousand people could live and be self sufficient without constant expensive resupply from Earth? Would we really colonize the near vacuum extreme conditions of Mars, when we don't even colonize deserts on Earth? However, a keen Mars colonization enthusiast will answer "Yes!" emphatically. Somehow all these problems will be solved, they say, and we will have colonies on Mars.

WHAT IF THE MOON HAD BLUE SKIES? ONE SMALL CHANGE TO APOLLO PHOTOS

I found, when writing this book , that the Moon is resource rich, and often beats Mars in habitability comparisons. Yet photos of Mars released to the press look so much more Earth-like, because of the brightening of the landscape and boosting of blue in the scene (white balancing) done to help geologists read the rocks. Many of them even have blue skies instead of the grayish brown skies natural to Mars.

So, what if we did the same with photos of the Moon, gave it blue skies too, like many of the Mars press photos? It's easy to do because the surface is already lit up just as it would be for a sunny day on Earth. We don't need to do anything else, just colour the sky blue instead of black, and it looks Earth-like already. I was amazed at what a difference such a simple change makes to the feel of the scene. You can read it as if illuminated on a sunny day, which is indeed what it was like for the Apollo astronauts.

So, here they are. These images are not altered in any way. All I've done is to crop them, and replace the black skies with photographs of blue skies and clouds from Earth.

Original here Apollo 17 at Shorty Crater - blue sky from here

Original here, sky from here

Original here, sky from here

For more examples, see my article: What If The Moon Had Blue Skies? One Small Change To Apollo Photos

It suddenly looks much more Earth-like. Yet it's a vacuum there. The thing is that of course it was a sunny day for the astronauts - you tend to forget when you see the black sky. On Earth some of the light comes to the landscape from the sun and some reaches us indirectly from the blue sky and the clouds.

On the Moon, much of the light comes from the sun, but a lot of light also comes indirectly from the landscape itself. That's why you can see detail in the shadows, and why they aren't completely black on the Moon. So - it's not quite so surprising as you'd think, but fun.

You can make the photos look even more like Earth by reducing the contrast - shadows are not quite so contrasty on Earth. I tried that and it worked. You could also fuzz the edges of the shadows as they are never so sharp edged on Earth, and you'd need to do something about the black sky reflected in astronaut's helmets. However I'm not trying to simulate an Earth illumination on the Moon. I don't have the skills anyway, there are graphics designers, artists, 3D modelers etc who could do a much better job.

But that wasn't my aim here. The aim was to show how the Moon is as Earth like as Mars in photographs, and indeed more so, with minimal processing, not even the white balancing they use for Mars photos. So to do additional processing to make it look more Earth like would rather defeat the point in the article. Perhaps others will do that in the future.

It's similar on the Mars surface, it is nearly as much of a vacuum as the Moon as far as humans are concerned. The moisture lining your lungs would boil there. Mars is not really significantly more "Earth like" than the Moon, I think.

This is a colour enhanced Mars image as you would see it in most press photos - enhanced for the purposes of geologists, so that the rocks look like the same types of rocks under Earth illumination. There are two ways to do this. The most common method is white balancing which takes the brightest patch in the scene, and adjusts it in brightness and hue until it is white. The other method, occasionally used, is natural colour which uses a calibration based on photographs of a colour swatch on Curiosity that was previously photographed on Earth.

This is what Mars would look like to a typical smartphone camera, the raw image from Curiosity (both these photos are of Mount Sharp)

Photos from here

I think the Moon would be a more interesting landscape to a human eye. Much brighter - which tends to make humans feel cheerful. While the sunlight on Mars at its brightest is half the illumination of Earth, and as well, it's a dull brown in colour with the Mars dust suspending in the air filtering out the blue. It has no blue sky except around the sun at sunset. Also there is very little variation in colour in the landscape. It's mainly dull grayish browns, with no blue and none of the bright glints catching the sunlight we have on Earth. I think that any Mars colonists would have a tendency towards depression just because of the rather gloomy sky and dull coloured landscape.

EARTH BEST FOR A "BACKUP"

I'll go into other aspects of this later on, but perhaps we should address this right away as it's become the top reason to attempt to colonize Mars for many people. Elon Musk has been promoting it strongly. Stephen Hawking has also said this is an important reason to go multiplanetary. In this account of an interview with Elon Musk, the author Ross Anderson presents it as:

"A billion years will give us four more orbits of the Milky Way galaxy, any one of which could bring us into collision with another star, or a supernova shockwave, or the incinerating beam of a gamma ray burst. We could swing into the path of a rogue planet, one of the billions that roam our galaxy darkly, like cosmic wrecking balls. Planet Earth could be edging up to the end of an unusually fortunate run."

But there are no figures here. So let's supply them. Calculation indented, and coloured dark red, to make it easy to skip:

That makes it about one chance in 2.8 million of a star passing closer to the sun than Neptune every million years. There may be twice as many rogue planets as stars, so that means one chance in 1.4 million of one of those passing closer to the sun than Neptune in the same time period. Neutron stars are even more unlikely. So we don't need to worry about any of these on the thousands of years timescale. The chances is less than one in a billion in the next thousand years that another star gets as close as Neptune.

Gamma ray bursts are possible also, but would not make humans extinct, even if very close. Our atmosphere completely shields us from gamma rays, which is why gamma ray telescopes have to be flown in space. We can only see gamma ray bursts at all with space observatories. The main effect is on the upper atmosphere and particularly the ozone layer. There was a theory at one point that this could through various interactions lead to increased nitrous oxide levels which could then lead to elevated ozone layers at ground level and so cause extinctions. However that theory has been shown to be false by more detailed modeling. Research announcement from NASA here: How Deadly Would a Nearby Gamma Ray Burst Be? Paper itself is here.

The gamma ray burst not only reduces the amount of ozone in the upper atmosphere. It also creates ozone depleting nitrogen oxides. They took the example of a gamma ray burst which hits the south pole most severely, as that has down drafts of air constantly. Those would bring the nitrogen oxides down to the lower atmosphere which is why you see the red regions descending with time. This causes a series of pulses of ozone depletion in the upper atmosphere which then leads to increases of ozone at sea level as the red regions let more UV through to the lower atmosphere. The model assumed a 100kJ/m2 burst from the direction of the South Pole, for a gamma ray burst within a few thousand light years of Earth (that’s very close compared to the diameter of the galaxy of 100,000 light years).

So could this raise the ozone levels enough to be harmful to life? The answer from this study was no. A very nearby gamma ray bursts could raise the ozone levels at ground level temporarily to 10 ppm. To be harmful to animal life it would need to reach 30 ppm. It is also not enough to be harmful to ocean life. Even if all the ozone created at ground level got absorbed in the sea, it would not be enough to be harmful to ocean life. So this disproves the hypothesis that a gamma ray burst could be the cause of the late Ordovician mass-extinction.

The idea that gamma ray bursts could cause extinctions at all, on any scale, is now not easy to establish. The main effect would be elevated levels of UV for a number of years. At any rate, if perhaps some other species were affected, they would not make humans extinct. Also the young Wolf Rayet stars which are gamma ray burst candidates are rare and of the hundred or so known, only one seems to be pointing our way. That's WR104, 8,000 light years away.

It looks as if it is facing us nearly face on. But spectroscopic observations of the star suggest it’s axis is at an angle of 30° - 40° (possibly as much as 45°) which would mean it would miss. See WR 104 Won't Kill Us After All - Universe Today

It's the same also for a nearby supernova. They are short, violent events, and again we are protected by our atmosphere from the worst effects, equivalent to ten meters depth of water in mass above us. See What’s a safe distance between us and an exploding star? And for more details, the paper here: Could a nearby supernova explosion have caused a mass extinction? They find that a supernova within 32 light years (ten parsecs), which should happen every few hundred million years would not heat up Earth significantly, would not be bright enough to harm the ecology through the light alone. In the year after the event you’d get as much ionizing radiation as you get normally in between a decade and a century. So the increase in ground level ionizing radiation is significant but it doesn’t seem to be enough to be devastating.

Also, are there any nearby supernova candidates? We can't predict when a star will go supernova exactly, but the only stars that can go supernova are ones that are at a particular stage in their life, and they have to be massive too, for Type II supernovae, and for type Ia it needs a white dwarf companion. Our sun can't go supernova at all, it's too light.

The Type II supernova candidates are easiest to see, bright massive stars, larger than our sun, which collapse to a neutron star or black hole at the end of their lifetime. Betelgeuse will explode some day, and we know this for sure. It could be today, but much more likely to be a long time into the future. It could be a million years from now. But it is far too far away to be any problem for Earth, nor is it close enough to be a second sun in our sky. It will just be a very bright star for us. It will be an interesting sight for astronomers, as a great chance to study a supernova close up. For everyone else, just a very bright star. Briefly, the brightest star in the sky. Betelgeuse will explode someday. Eta Carinae is another star that can go supernova. It’s a “blue supergiant” - which shows it’s not just red giants that can go supernova. This is a very young, super hot star 8,000 light years away and it may explode in the next few hundred thousand years. It’s also far to far away to harm us.

The other type of supernova is a Type Ia supernova (with some variations on it). A red giant star dumps gas on a white dwarf companion. These used to be the "dark horses" which we couldn't detect easily, leaving the possibility that there might be a nearby one that would cause problems. But with all the modern sky surveys, we now know that there are no nearby candidates for a type Ia supernova either. The closest is IK Pegasi which at 150 light years away is far too far away to harm us. It’s moving away from us and the scientists think it won’t go supernova for several million years, by which time it will be perhaps 500 light years away. It would need to be within 30 light years to be harmful. There are type Ib and type Ic supernovae too, These happen when a star loses its outer envelope, for instance to a companion star - and then the naked core collapses. Type Ib and Ic supernovae. But there are none of those nearby either.

Here is a list of the nearby List of supernova candidates See also: The closest supernova candidate? - Bad Astronomy So, though a nearby supernova within 30 light years could harm our ozone layer, right now there are no candidate stars that could go supernova, that are close enough to harm us. We get supernovas quite often and they leave rather beautiful remnants. Roughly once a century, though many are so obscured by dust and gas that they can't be seen with the naked eye from Earth. For instance Cassiopeia A which was recorded in the mid seventeenth century as very faint sixth magnitude star by John Flamstead on August 16 1680, he didn’t know what it was. For more details see my Debunked: Earth is threatened by a supernova

For those that worry about such things, I'd like to just add, that both of these are extremely unlikely events, and there are no known stars likely to go supernova close enough to be a hazard right now. The next supernova is most likely to be thousands of light years away, since we can spot them so far away. They are rare events that happen occasionally in an entire galaxy, and can be seen from an immense distance, and are most often spotted in distant galaxies as well.

The important thing is, that none of these would make Earth less habitable than Mars. It would still have its oceans, its oxygen rich atmosphere, its protection from cosmic radiation, its land, its plants and surely fish and shellfish and animals also.

Even after the extinction of the dinosaurs, birds, dawn sequoia, river turtles, small mammals and many other plants and creatures survived. Many species would go extinct after a gamma ray burst or a large asteroid impact, but humans are great survivors and can survive anywhere from the cold Arctic to the hot and dry Kalahari desert, with only neolithic technology. So some of us, surely, would survive. And there is no realistic chance of a significantly larger asteroid, as there are no impact craters that large anywhere from Mars inwards dating from later than 3 billion years ago.

If your "backup" is on Mars, then after something devastating happens, obviously you'll have rebuilding Earth as your top priority, as it is going to be far easier to restore Earth than to attempt to terraform Mars. So you've got your backup in the wrong place, six months travel by space from the place you will need to help rebuild.

You could do a much simpler backup, if you think it's necessary, by simply setting up your Mars base on Earth, in three different locations, say, in order to make sure they aren't all destroyed at once. Most of the technology you need for Mars is not even required. By putting your backups on Earth, the inhabitants don't need to worry about the need to maintain a breathable atmosphere, and can go outside and repair their habitats without spacesuits, and don't need to cover the habitats with meters of regolith to protect from cosmic radiation and solar storms. It would cost only a fraction of the cost of a Mars facility to set up such facilities on Earth, and the facilities. Even if they go everywhere in biocontainment suits, it's far easier than using spacesuits. And In Situ Resource Utilization is obviously going to be far easier on Earth no matter how devastated, than on Mars.

So, it just doesn't seem to add up. Extinctions are happening, and will surely continue, many of them human caused. But humans themselves going extinct? I can't see it. And surely the Martian colonist, so highly dependent on technology, would be the most vulnerable of us all if we somehow have a breakup of society and lose our ability to use technology? I don't see that happening anyway, but if it did, why would it be restricted to Earth, and Mars be immune? Without modern technology they would have no chance at all on Mars.

That is, unless we go extinct through misuse of technology. Nick Bostrom is a philosopher who thinks we have a high risk of going extinct from use of our own technology, perhaps as high as 25%. But that's partly because he is one of those who think the "singularity" is a possible future scenario, complete with mind uploading and boot strapping super intelligences who might take over the world. He also thinks that we might be living in a simulation which gets switched off. Elon Musk also thinks those are possible, as you can tell from the interview. Myself, I think those are both science fiction scenarios that probably don't correspond to anything in reality. In any case both of those scenarios would impact both Mars and Earth equally.

I see the greatest potential risks as from synthetic biology, for instance experiments to modify living cells to use something else in place of DNA, or from return of an extraterrestrial biology to Earth. See my Could Anything Make Humans Extinct In The Near Future? for the reasoning there.

In any case, if the main risk of extinction is from our own technology, then how can the solution be to set up a new society in space that is more dependent on technology than any other society that there's ever been? The Martian colonists could well be the ones that create the devastating technology in the first place, if such is possible at all. This could even increase the risk, by deflecting attention and money away from preserving Earth, and if done rapidly, even by causing conflict situations in space too. A war between space colonies would surely end quickly with nearly everyone dead, with such powerful technology and fragile habitats.

And as for quarantine ideas - if it is quarantine that is the safety net, it would be easy to set up our "backups" on Earth with quarantine periods. And the six months voyage to Mars would surely get shorter, weeks, maybe even go down to days eventually, as transport gets better.

So we can't rely on the distance to Mars for quarantine. Anyway, if it's a disease spread naturally, then if it is too virulent it doesn't spread far. It's not in the interest of a disease to kill its host, especially quickly. As a result there's usually some natural immunity. Even the great plague didn't kill everyone. The diseases also needs some way to get transmitted, for instance through sneezing, carried by rats (as in the case of the great plague) or whatever. It's surely very unlikely that some plague like that would kill everyone on Earth without exception.

It is possible if something else reduces our population to a small number, say a few thousand, first in a "human bottleneck". That may have happened to humans in sub-saharan Africa, before they spread to Europe and India, as recently as 70,000 years ago, just locally. At that point the human population may have been reduced to as low as 2,000. This extinction event of course does not apply to the other hominids that had left Africa millions of years ago (in the case of Homo Erectus) and hundreds of thousands of years ago (in the case of H. Heidelbergensis, likely ancestor to modern humans, Neanderthals and Denisovans). There were plenty of intelligent hominids living outside Africa at the time, and they didn't go extinct until much later as a result of competition with modern humans. It's just that they were Neanderthals and Deinsovans rather than Homo Sapiens.

Also, those 2,000 people, though they probably had fire and the ability to make log boats, may or may not have had clothing, and didn’t have the most basic ideas of modern science. Most especially, they didn’t have agriculture. That didn’t happen until 10,000 BC onwards: Neolithic Revolution It wouldn’t have occurred to them to try to cultivate plants or animals or birds, fish etc for food. How likely is it that some global catastrophe causes all humans to lose their knowledge even of agriculture?

Meanwhile any colonists on Mars might be the very people that introduce extra terrestrial microbes from Mars to Earth, or develop some synthetic biology to use on Mars that gets out of hand. Also if somehow civilization collapses, e.g. if we no longer can make computer chips - who would be first affected? We could get by on Earth, it would be a nuisance, but many would still survive here without computer chips. The space colonies would be the first to go in that situation I think, as it's hard to imagine a space habitat functioning without computer chips. It will be a while probably before they can make computer chips. And if they can survive the collapse of civilization on Mars, surely there will be communities on Earth that survive too, and end up in a much better situation, materially, than the Martian colonists with their small pocket of technology on a barren planet.

So, it seems that the technology dependent humans on Mars will go extinct much more easily than humans on Earth in the event of our civilization somehow forgetting technology. If they can't import computer chips from Earth and either don't have the ability to make computer chips on Mars, or somehow have lost that ability, that's probably the end of them. But on Earth we could get by without computer chips. After all we managed without them right up to the middle of the twentieth century. Early twentieth century humans could not possibly have survived on Mars. We could make do here without radio, without television, even without internal combustion or steam engines, still many would survive on Earth. Nobody could survive for long on Mars without late twentieth century technology, and continual resupply from Earth, or some future twenty first century technology that we don't have yet.

So, I think as far as preserving our civilization, space settlement and colonization is pretty much neutral. It might help in very rare situations, might make things worse in other situations, or might make no difference at all. But as a backup, it's doing nothing. Not at current levels of technology.

So, I don't see this as a good motivation for sending humans into space. Rather, it's a motivation for setting up backups on Earth, if you think this is a serious risk. Plus taking great care about new technological developments that could lead to any kind of an extinction risk, such as synthetic biology, or return of extraterrestrial life to Earth.

Carl Sagan expressed a similar sentiment in Pale Blue Dot

"The Earth is the only world known, so far, to harbor life. There is nowhere else, at least in the near future, to which our species could migrate. Visit, yes. Settle, not yet. Like it or not, for the moment, the Earth is where we make our stand."

Maybe half a billion years from now it will be a priority to set up habitats elsewhere, for whatever intelligent creatures have evolved on Earth by then, or they might have other solutions to the future hotter sun, such as shades in orbit, or moving Earth, but it's not urgent right now.

To be clear, this is not at all an argument against settlement. I think settlement in space is likely to happen, and can be beneficial if done well. But I think the motivation for it matters. More on this below under Earth is the best place for a backup, where I link to some of my other articles as well.

This argument might be a good motivation for setting up backup libraries and other archives, but if so, the aim would be to restore Earth after a disaster, so those would be best as close as possible, for instance on Earth itself, or on the Moon, for this, see Backup on the Moon - seed banks, libraries, and a small colony

BUT WOULDN'T IT BE THE MOST WONDERFUL THING TO INTRODUCE EARTH LIFE TO MARS?

Some enthusiasts say, that no matter what happens, whether it makes Mars better for humans or not, that it would be the most wonderful thing we could do, to introduce Earth microbes to Mars, and more generally, spread Earth life throughout the universe in this way.

This is similar to the idea of introducing rabbits to Australia.

"Rabbits were introduced to Australia by the First Fleet and the first feral populations were established in Tasmania by 1827. The Victorian Acclimatisation Society released 24 rabbits on Christmas Day 1859 to hunt for sport and to help settlers feel more 'at home'. "By 1886, rabbits had spread as far as the Queensland-NSW border and by 1900 they had reached Western Australia and the Northern Territory. In the 60 years following 1886, rabbits invaded 4 million square kilometres of Australia, making it one of the fastest colonising mammals anywhere in the world. 'Competition and grazing by rabbits' was listed as a key threatening process by the NSW Scientific Committee in 2002."

So, they did it for similar, and understandable reasons. To help settlers to feel at home and because they felt rabbits were good things to have in Europe to hunt for sport, and so would be in Australia too. They had no idea what the consequences would be for Australian wildlife and indeed for Australian farmers too, They say in that same fact sheet that

"It has been estimated that Australian agriculture loses more than $115 million a year because of overgrazing by rabbits. "

Many other animals have been introduced to Australia and cause problems, even large animals like camels and donkeys, which are hard to control over such a large continent, and including the feral cat. Again it might seem wonderful to introduce the friendly lovable kitty to Australia, but it has made small species of mammals extinct or set back attempts to help them to recover. The domestic cat is listed as a key threatening process for Australia.

It may seem wonderful to introduce the familiar Earth microbes to Mars, but when you think through the consequences, it might not be as wonderful as you think. It's important to look ahead and look at the consequences of your actions.

Rabbits have been eradicated from islands, and they are easily visible, large creatures. They can be kept out of smaller areas with fences. In principle you could even remove them from Australia in its entirety, and even more so the camels, donkeys etc.

However, if we introduce a microbe to Mars, and it is able to survive in some habitat on there, then there is no way it can be removed again, ever, for all future time, for as long as Mars remains habitable to them. Also there is no way to fence off part of Mars to keep it out.

If we look at the many possible consequences of introducing Earth microbes to Mars, some of them lead one to pause and wonder if this is such a good idea as it might seem at first. Both for humans on Mars and for any native life there as well. The repercussions, I think, could be far worse than the repercussions of introducing rabbits to Australia to make the settlers "feel at home".

PLANETARY PROTECTION

Before I go any further, I'd better introduce the idea of "Planetary protection", as I talk about it a lot here. Some of you might think it's protection from meteorites and such like disasters. And yes that's important and I'll cover that too, but usually the phrase is understood in the sense of the Outer Space Treaty, and particularly article nine, as referring to harmful contamination of other bodies in the solar system by materials from Earth, and adverse changes in the environment of Earth from return of extraterrestrial matter:

"Article IX: ... States Parties to the Treaty shall pursue studies of outer space, including the Moon and other celestial bodies, and conduct exploration of them so as to avoid their harmful contamination and also adverse changes in the environment of the Earth resulting from the introduction of extraterrestrial matter and, where necessary, shall adopt appropriate measures for this purpose." (emphasis mine)

All space faring nations and most with space faring aspirations, all have signed it and nearly all have taken the additional step of ratifying it (formally indicating its consent to be bound by the treaty, a process that varies according to the country but for most democracies involves passing a bill in parliament). The only states with space faring aspirations who haven't ratified it yet are the United Arab Emirates, Syria and North Korea. It's signed and ratified by 104 states so far in total.

There's no sign that anyone wants to evade these provisions, and indeed even those who haven't ratified the treaty are keen to abide by the provisions. Cassie Conley said recently on the Space Show that she was approached by the UAE who have ideas for a robotic mission to Mars, asking for advice to make sure they comply with the planetary protection provisions of the OST.

Also, it already it has the status of customary international law because of the consistent and widespread support of its fundamental tenets, and because it is based on a 1963 declaration that was adopted by consensus in the UN National Assembly. This means that it is binding on all states, even those who have neither signed nor ratified it. See page 220 of this paper.

The central phrase here is "harmful contamination". All of our planetary protection policies are based on interpretations of that phrase. The currently widely accepted customary interpretation is that

“any contamination which would result in harm to a state’s experiments or programs is to be avoided”.

NASA policy states explicitly that

“the conduct of scientific investigations of possible extraterrestrial life forms, precursors, and remnants must not be jeopardized”

The treaty covers all forms of contamination, but most especially, the aim is to protect other planets from self replicating Earth life and to protect Earth from extra terrestrial life returned from space. Discussions focus on microbial life transferred in either direction. Carl Sagan worked out the earliest recommendations with other researchers in the 1960s such as Joshua Lederberg, Nobel prize winning microbiologist, and one of the first astrobiologists.

The guidelines evolve to meet new situations, and details are now hammered out in international workshops of scientists. It's one of the functions of the Committee on Space Research (COSPAR). Every two years they meet to work out details of what is required for all the places we send spacecraft to, or may send them to in the future. The US has a planetary protection office, and a planetary protection officer, Cassie Conley. ESA's planetary protection officer is Gerhard Kminek. All space faring countries follow these guidelines when they send their spacecraft to vulnerable places in the solar system.

Planetary protection just makes sense here. It's easy to find life in habitable places in our solar system; just bring it with you. But that would be the worst possible anticlimax of all our searches to try to find life on Mars or elsewhere in our solar system, and would greatly diminish the scientific interest of Mars. Mars is a high risk target (category IV) in the forward direction, from Earth to Mars, and our robotic missions have to be sterilized if they land on the surface. There are several levels of sterilization depending where you go on Mars, with the highest level, IVc, for missions that approach places on Mars which could be habitable to Earth life. Curiosity is not sterilized to this highest standard so if it found a potential habitat on Mars, it could only observe it from a distance. Indeed, the team are facing this quandary right now, as there's a potential flow of seeps of salty liquid on the higher slopes of Mount Sharp which is within its range. But because Curiosity is not sufficiently sterilized, they will only be able to photograph them from a distance, and even then it's a decision that needs careful thought, to go close enough to photograph them.

The Moon, by comparison, is low risk (category II), as COSPAR scientists think there is no chance of Earth life reproducing there. The only requirement is to document anything you land on the Moon, including any crash landings and deliberate impacts. We have sent Earth life to the Moon already, in all our spacecraft as hardy spores clinging to the equipment, and as human wastes also in the case of the Apollo spacecraft. But that's no problem. The scientists believe that it will stay where you left it, or not be transported far in the processes that operate on the Moon, and as long as you document what you did clearly, follow up missions will be able to allow for it. The Moon is large enough so that some organic human wastes in one place will not matter for other missions even just a few kilometers away. So there's no problem sending humans to the Moon.

COSPAR don't yet have definitive guidelines for humans to Mars. Before they could publish these guidelines, they would need to meet to discuss what planetary protection measures are needed. And actually, there have been several meetings already of this type, and they all concluded that we don't yet have sufficient data for detailed guidelines. I think actually that if asked to approve a mission as soon as the 2030s, there might be a divergence of views. There is no way they'd have enough data by then to be able to make an authoritative decision, not unless we manage to send dozens of robotic missions to Mars in the next couple of decades (unlikely). I go into this in a fair bit of detail in the section on Searching for a non confrontational way ahead

In the other direction, backward contamination, returning materials from Mars, it is classified as restricted category V. This means that many precautions need to be taken in the case of a sample returned from Mars, also new laws would need to be passed, domestic and international, to protect Earth from Mars life. Depending on what we find on Mars, it could be that Mars life would do us no harm at all (for instance in an early life scenario, long made extinct by DNA life on Earth), or it could be that we need to take great care. For instance, if there is independently evolved advanced microbial life on Mars, the risk from a sample return could be similar to that of releasing new synthetic forms of microbial life into the wild from our laboratories. For these reasons and others, I think that the search for life on Mars is also best done in situ at present - you may be interested in the reasons given there.

WHY DO MICROBES ON HUMAN OCCUPIED SPACECRAFT GET A "SPECIAL PASS" TO MARS?

So, with this background, you can also ask the advocates for humans on the Mars surface, why land trillions of Earth microbes on Mars when you are searching for life there? With our robotic missions, we continue to sterilize as carefully as before, with no sign of any suggestion that we can relax the planetary protection requirements. Indeed, for robots, the trend is towards more rather than less by way of planetary protection.

So, what is special about all the microbes that hitch a lift in human occupied spacecraft? Why give them special treatment? Would it not be more sensible to keep them well away from the planet too, until we know what effect they will have?

That may seem far fetched, that Earth microbes would matter to Mars. But travelers from Hawaii have to be careful not to bring the oriental fruit fly Bactrocera Dorsalis into California because it would devastate the crops. It's rather like that.

Bactrocera dorsalis - a female oriental fruit fly. Travelers from Hawaii to California have to be careful not to introduce it, as it makes fruit unfit to eat. Similarly microbes from Earth introduced to Mars may have harmful effects on whatever is on Mars, for instance, if Mars hosts some vulnerable form of early life that has been made extinct by DNA based life on Earth. But it's not so easy to prevent Earth microbes from entering Mars on a human ship.

It would satisfy nobody to try a compromise solution for Hawaii imports to California, e.g. to import fruit only on the first day of each month. That would mean the fruit importers are severely restricted in what they can do, while the fruit growers are not protected from the oriental fruitfly, so it satisfies nobody.

In the case of human missions to Mars, I think everyone would agree that a crash of a human occupied spacecraft on the Mars surface, with provisions, air, water and human bodies, with the trillions of microbes that accompany us strewn across the landscape, would be pretty much an immediate end to planetary protection of Mars. Can we have 100% reliable landings of human occupied spacecraft on Mars? We are nowhere near that level of confidence with robotic spacecraft.

And indeed Elon Musk in an interview with the Washington Post about his ideas acknowledges the risks:

“the first mission wouldn’t have a huge number of people on it, because if something goes wrong, we want to risk the fewest number of lives as possible.” “It’s dangerous and probably people will die—and they’ll know that,” he continued. “And then they’ll pave the way, and ultimately it will be very safe to go to Mars, and it will very comfortable. But that will be many years in the future.”

How can that approach be kept consistent with planetary protection for Mars? Well Elon Musk thinks there are probably no habitats for life on the surface; only deep underground. There's no problem with astronauts who volunteer to take huge risks exploring asteroids, or the Moon or anywhere else uninhabitable for Earth life. But is that the situation on Mars?

This is an article and kindle booklet I wrote about this:



Can We Risk Microbes From Human Crashes - On Mars? If Not, What Happens To Dreams To Colonize The Planet?

For more on this, see Searching for a non confrontational way ahead

But all this so far is negative vision. It's not going to inspire people. Again the colonization enthusiasts will agree that this would be the ideal way to proceed. However they will say that colonizing Mars is so important, that they have to go ahead anyway. They will say that we have no evidence that our microbes can cause any harm on Mars yet. And they will assure you that they will take the best precautions they can to protect the planet given the requirement that they have to land humans on Mars as soon as possible. The ones who think that there could be habitats for Earth microbes on Mars may go on to say that some irreversible contamination with Earth life is inevitable, so we just have to find a way to cope with that.

NEED FOR VISION AND INSPIRATION

Humans need vision and inspiration, I agree. If you just say "can't do this, don't do that" that's a negative vision that can't inspire anyone. We need a positive vision if we are going to have any alternatives to this Mars colonization idea for the future.

So, I think I'm trying to develop an alternative positive vision here. Whether it works or not is something I'm finding out. It's getting enough favourable attention to be encouraging. In the process I've also come across others with alternative visions of their own. So perhaps it might encourage them too to continue to develop their visions and present their dreams.

The more visions we have, the more options we have for the future. It is hard to present a vision like this in a short period of time. Remember that the positive vision of Mars colonization has many details to support it, built up by its advocates over books, talks, television programs and so on, for decades. So an alternative positive vision also has to be quite detailed. This book, though it is quite long, is a rapid summary of just the main ideas.

Also, I'd also just like to say at the outset to humans on Mars enthusiasts, that "This approach doesn’t mean that humans can never land on Mars ever". It's the microbes that are the planetary protection issue here, not humans. And the microbes are an issue right now because we don't know what is on Mars, or what effects our microbes will have on the planet. I will suggest that whether microbes continue to be an issue in the future, or whether we can relax planetary protection measures for Mars, is something we can only find out by studying the planet in much more detail than we have so far.

THIS BOOKLET OUTLINES ONE PARTICULAR VISION OF MANY

The main new thing about this booklet compared to other treatments of the subject is that I put planetary protection, the value of science, and reversible biological exploration as central core principles from the outset. Often these topics, especially planetary protection, are barely mentioned.

I outline one particular vision here and present my own views unashamedly. I expect most readers will agree with me on some points and disagree on others. My main aim here is to present a vision in enough detail to stimulate discussion about other possibilities for future alternative visions. There could be many other ways to develop such a vision.

POSITIVE VISION FOR HUMANS IN SPACE

The key point here is, that while we continue to explore other places in the solar system with robots, we start with the Moon, for humans, as a place of great interest in its own right, and not just as a step on the way to Mars.

This is an important part of the vision, so I'll open out by talking about how interesting the Moon is, in some detail. It's our first place to explore on foot outside of Earth, and a gateway for humans to Mars, Venus, Mercury, the asteroids, Jupiter's moon Callisto, and further afield. If we develop the ability to live in space for years at a time on the Moon, then the whole of the solar system will open out to us, and we won’t need to be focused on humans to Mars as the only option.

Artist's concept of a permanent lunar base, credit ESA.

Screenshot from ESA Destination Moon video.

In this article I use "space settlement" as the more general term, to refer to any humans living in space in permanent or semi-permanent bases, as they do in Antarctica - and space colonization for some later stage when they may become more self sufficient and also have children born in space.

It is likely to be a progression, first with outposts only temporarily inhabited. Then bases, like an Antarctic base. At some point, perhaps quite early, these become materially self sufficient in many things, able to produce all their own food, recycle their water, and produce power and even fuel for their rockets in situ. But they would be dependent on Earth for other things like spacesuits, computer chips, clothes, experimental apparatus, and any other complex machines and hard to manufacture materials. At some point we get the first children born in space, and then we may get the beginnings of true colonization.

But, I argue, colonization is perhaps not the best goal to have in the early stages. We may miss many opportunities if we make this our main aim, rather in the same way that if the early Antarctic explorers had had as their main aim to colonize Antarctica, they would surely never have succeeded in this, and would have missed out on the many discoveries and advances in science that came from a more open ended approach.

THE MOON IS RESOURCE RICH

Mars colonization advocates often contrast Mars with the Moon. The Moon may be described as being as uninteresting for human colonization as a lump of concrete. But actually it turns out that the Moon is very rich in resources. We need a "Case for the Moon" here like Robert Zubrin's "Case for Mars".

Moon advocates perhaps don't hit the news as much as the Mars advocates but there are many of them, and they are just as enthusiastic about their vision as the Mars advocates. Paul Spudis is one, with his most recent book, The Value of the Moon: How to Explore, Live, and Prosper in Space Using the Moon's Resources. Another is Dennis Wingo, CEO of Skycorp, and author of Moonrush, see his recent paper, and appearance on the Space Show. Others include Madhu Thangavelu, David Schrunk, and other authors and contributors to The Moon: Resources, Future Development and Settlement. See also David Schrunk's paper Planet Moon Philosophy , and their appearance on The Space Show.

It was also the policy of the US too during the Bush administration, with his Vision for Space Exploration program. And the ESA and Russia are strongly behind the idea of sending humans to the Moon first.

So, let's look at some of the suggested lunar resources for this Moon first approach.

CO 2 ON THE MOON

The Moon doesn't have a CO 2 atmosphere, but it has dry ice at the poles. It has an estimated at least 600 million metric tons of ice (based on the mini SAR and lunar prospector data, indirectly detected through radar), and possibly much more. If the proportions are the same as for the LCROSS impact measurements, 2.12% of that may be CO 2 , so if those figures are correct (which needs more confirmation), that could be more than twelve million metric tons of CO 2 in the form of dry ice.

That's plenty, but we might not even need it. It is only a trace gas in our atmosphere, less than 0.04%. And, this may surprise you, but actually, feces is nearly all water. About 1 kg of carbon dioxide is exhaled every day, compared to only 30 grams (0.03 kg) of dry weight in feces.

Plants don't need a constant supply of carbon dioxide from outside of the habitat. Indeed, if you grow enough plants for food, then they get all they need to make the plant matter and the oxygen from the carbon dioxide you breathe out, and a small amount from the feces which can be burnt or composted.

With each crop, to close the cycle, the plants also produce almost exactly the amount of oxygen that humans need to breathe, indeed that's the main advantage of growing your food, that it saves on the 0.84 kg of oxygen you need to supply per crew member every day (from table 2 of this paper). Oxygen supply is the main issue here, and after that, food.

If you have to import some of your food, as has always been the case so far, then an excess of carbon dioxide builds up, and you have to remove because it is dangerous to humans long term at concentrations of above one or two percent in the atmosphere.

The first crop cycle, for, say, 40 days (it took 39 days for dwarf wheat to reach maturity in an experiment on the ISS in zero g) does need a net input of CO 2 to the plants for them to grow. But this will be provided by the astronauts just breathing it out, so if you supply them with food for the first month, then they will then provide enough carbon dioxide for the next crop cycle onwards.

Or if you use robots to set up the greenhouse before the astronauts arrive and bring the first crop to maturity ready for them to eat, then you need to supply that 1 kg a day of CO 2 per astronaut for one month. So that's 40 kg per astronaut.

You could take carbon out of the atmosphere in the habitat if you store and accumulate the plant wastes. Typically half the crop is plant wastes and if you stored all the plant wastes, yes, you'd need a constant input of CO 2 . However that would lock up valuable oxygen into the plant wastes and remove carbon from the system as well, so it's not too likely that you would do that.

If you burn plant wastes too as is the most likely thing to do in a space colony, or compost them, then you have a closed system, and any imported food will mean an excess of carbon in the system which will build up in the atmosphere rather rapidly. This was the main thing that threatened the lives of the Apollo 13 crew, they had plenty of oxygen but had to rig up a way to scrub the carbon dioxide to survive.

On the ISS it used to be vented into space. Nowadays they react it with the hydrogen got from splitting water to generate oxygen, in the Sabatier reaction This converts the carbon of the carbon dioxide to methane which is then vented into space. That's still not a closed system as it depends on constant input of water and food to provide the carbon and hydrogen that's lost to space in the methane.

The ISS's half kilogram for 0.04% (see next section) would then correspond to just half a day's worth of wastes for one person. If you suppose similar amount of atmosphere to the ISS, and six people, importing all their own food, the carbon dioxide would build up at a rate of about half a percent a day, so would over 1% within two days, and reach 10% within 20 days, a level which leads to convulsions, coma and death.

If they import half their food, and don't scrub the carbon dioxide they die within 40 days, but probably much sooner. If they import a quarter of their food, with no carbon dioxide scrubbing, they die within 80 days.

That's based on this paper which says concentrations >10% may cause convulsions, coma and death. That's for short term exposure, so with continuous exposure with gradually increasing concentrations, they would probably die well before then. Levels of up to 3% however can be tolerated for more than a month without any adverse effects (see table 2 page 66b of this paper).

No space habitat to date has had to import CO 2 , and until you have near perfect recycling it won't be needed. Once you are able to grow all your own food, then you may need a tiny amount, but the more perfect the recycling, the less you need. If you had perfect recycling, you'd only need as much as is necessary to get the plants started. Usually half of the plants grown for crops consist of plant wastes, but that also doesn't really change anything. The CO 2 you get from burning the wastes or composting it, added to the CO 2 breathed out by humans, is almost exactly the amount the plants need to grow the next generation of crops.

So, it's not too likely that you will have a shortage of CO 2 in space.

One way or another, if you import food, you will have an excess of carbon in the system which has to be scrubbed and got rid of somehow, usually as carbon dioxide or methane. While if you manage a nearly biologically closed system, you need hardly any materials supplied from outside to keep it going, just need to deal with leaks. The water in urine, sweat and grey water can be recycled, something that is already done in the ISS. For techy details: upgrades to the ISS water recovery systems. The feces can be dealt with also, without need to build a sewage plant in space, for instance oxidized at high temperatures 400 C and high pressures using supercritical water.

It's true that in the carbon cycle on Earth, volcanoes recycle carbon dioxide, which was originally taken out of the atmosphere millions of years ago, however not by us eating plants, or plants just growing and decaying as that returns roughly the same amount to the atmosphere as was taken from it. It is taken out through steady build up of plant residues, for instance peat, coal and oil, and through build up of limestone and chalk in the oceans and through organics falling into the ocean from algae growing on the surface. Most of our CO 2 is stored in carbonates such as limestone, or as organics in the oily shales, and that's what gets subducted and then returned to the atmosphere in volcanoes. It's a much slower process.

If we ever attempted to terraform Mars or the Moon or anywhere else long term, we would need to have some other way to return the limestone and chalk and other carbonates to the atmosphere, as it doesn't have continental drift to subduct them and cycle them around through volcanoes. However this is not a concern for space habitats in the near future - they aren't going to be troubled by the effects of a build up of oil rich shales, limestone and chalk.

For more about all this see my Could Astronauts Get All Their Oxygen From Algae Or Plants? And Their Food Also?

NITROGEN

Moon has nitrogen too, in the form of ammonia at the poles. If it is correct that there are 600 million tons or more in the form of ice up to 2 meters thick, with 6% ammonia, then there may be 25 million tons of nitrogen there .

We need nitrogen as a buffer gas in the atmosphere to protect us from oxygen toxicity.

There is another way to avoid oxygen toxicity, and that is, to use oxygen at low pressures, as they do for spacesuits. Spacesuit gloves are stiff and difficult to use and full Earth pressure would make them much harder to use. Apollo also used a pure oxygen atmosphere even after the fire of Apollo 1, as a simpler system, but you have to take care to use materials that won't burn easily. Since Apollo all space flights have used mixed oxygen / nitrogen for habitats and pure oxygen only for spacesuits. So, lunar habitats will surely do the same.

We don't have to keep resupplying nitrogen to a space habitat because it is a one off amount of mass (plants use nitrogen but it's part of a nitrogen cycle so could be returned to the atmosphere using denitrifying bacteria, and anyway compared to carbon, it is a small amount of the total mass of the plant). So how much mass do we need to provide?

Well, ignoring reserves of nitrogen, we can work out how much is needed for the habitat air itself. The pressurized volume of the ISS is 32,333 cubic feet or around 915.5686 cubic meters. At 1.225 kg / m³, at Earth sea level pressure which is what they use, it's 1.122 tons of air. So that's less than a ton of nitrogen, and of the total mass of the ISS, 419.725 tons, only 0.27% is atmosphere. As for CO 2 , at 400 ppm, that much air would contain a negligible half a kilogram (0.04% of 1.122 tons)

So, it's useful to be able to get your nitrogen and oxygen in situ, but it's not a deal breaker if you have to get it from Earth if you have decent closed system recycling.

It's the same for any size of habitat, for city domes too, the atmosphere is small fraction of the total mass, not including regolith shielding, just the unshielded habitat mass.

For a large habitat such as the Stanford Torus then the atmosphere is a higher percentage of the total mass, but that's because it has less structural mass needed, because the surface area (heaviest part) goes up only as the square when the volume goes up as the cube.

For the Stanford Torus, the structural mass is 150,000 tons, atmosphere 44,000 tons, for 10,000 people.Per person that's 15 tons of structural mass and 4.4 tons of atmosphere, not counting the regolith shielding (which they planned to send from the Moon using bulldozers and a mass driver)..

For the ISS, with 6 people, 419.725 tons, that's about 70 tons per person of which 0.187 tons is atmosphere That's a fair bit of atmosphere. There are more efficient ideas for the Stanford Torus, the Vademecium design which has a flatter torus so reducing the amount of mass for atmosphere. However, the reduction in structural mass compared to the ISS more than compensates.

The situation is the same for most large space habitats. The larger it is, the less structural mass per person but the more atmosphere per person if it is similar in shape to a smaller habitat. Venus cloud colonies are different, they have much lower mass requirements per person similar to an airship, and in principle, they can get all of their atmosphere from the Venus atmosphere too.

Nitrogen doesn't seem likely to be a major issue in the early stages at least. It may be more of an issue if we wish to fill an entire lunar cave with nitrogen, more on that below: Can we fill lunar caves with air.

LUNAR CAVES

We can only see a few meters into the lunar caves from the surface, so we don’t know how far they extend, especially since the regions near the pits are probably partly filled in with debris as well. But they could be huge; potentially they can be large enough to fit in a large city, the size of Philadelphia, with space to spare

Such huge caves are only possible because of the low lunar gravity, as they would collapse on Earth. Similar caves on Earth are far smaller as would be any similar caves on Mars. We don't know for sure if such large caves do exist, but it does have many cave entrances photographed from orbit, which proves that at the least, it has caves with entrances similar in size to Earth cave entrances. Then the extensive systems of rills and the Grail data are suggestive of larger caves to be discovered.

Some of the possible lava tube gravitational signatures are over 100 kilometers long and several kilometers wide. If the Moon does indeed have caves 100 km long and kilometers wide, that's similar in size to the O'Neil cylinder space habitat with a land area of several hundred square miles (the O'Neil cylinder consists of a pair of cylinders, each 20 miles long and 4 miles in diameter, with total land area 500 square miles).

Each such cave could house several million people. This may be a long shot, but isn't it amazing, to think that the Moon could have caves as vast as this, similar in size to an O'Neil cylinder, and we simply wouldn't know yet?

EXAMPLE LUNAR CAVE SKYLIGHTS - LACUS MORTIS, MARIUS PIT AND THE KING-Y NATURAL BRIDGE

The Lacus Mortis area has possible volcanic cinder cones, as well as the more common shield volcano features, rilles, and a partially collapsed cave entrance with a gentle slope leading into it. This was the proposed destination for the Astrobiotics mission in 2014.

Partially collapsed "skylight" in the Lacus Mortis region of the Moon.

Photos of the Lacus Mortis pit from various angles, which were used to build a 3D model of the pit, assuming that it is a cave entrance.

3D model shown from various angles. The cave was assumed to be oval shaped as a result of fill by debris form the collapse - further from the entrance, if it's a lava tube cave, it should widen out to a circular cross section.

3

One of two possible volcanic cinder cones in the Lacus Mortis area. Though the Moon has many rilles and shield volcanoes, volcanic cinder cones are very rare indeed, if that is indeed what this is.

Another interesting pit is the Marius Hills pit entrance, original destination for astrobiotics:

The "skylight" on Marius hills (see page 7) was the original objective for the astrobiotics Skylight mission as envisioned in 2013 - it may be an entrance to a much larger lunar cave as it is located on a lunar rille

This shows the topography - it's about 40 meters deep The crispness of the landform suggests the collapse happened less than a billion years ago, and the lack of any raised rim or eject suggests it formed through collapse, not through a meteorite impact.

This image shows an oblique view. It's viewed from an angle of 45 degrees, and the light from the sun is at an angle of 34 degrees from the vertical. As a result they were able to confirm that the area of the floor illuminated in this image continues at least twelve meters under the overhang. Papers here, and here .

This shows the location of the Marius pit along a lunar rille. Image from page 5 of Exploration of Planetary Skylights and Tunnels

Another "honorable mention" goes to the region of King crater, which is of special interest for its remarkable natural bridge.

Lunar natural bridge feature King Y, probably caused by a double collapse. It's about 7 meters in width and a 20 meters walk to cross it.

The lunar caves may also have unusual minerals that formed as the lava that created the cave slowly cooled and differentiated.

The NASA PERISCOPE project, currently a phase II concept study, could potentially give us a way to see into lunar caves from orbit using femtosecond laser photography which lets you "see around corners" to parts of the cave that were never within the line of sight of the orbiter.

We may may get our first views into the interior of a lunar cave from ground level some time in 2017, with the Japanese Hayuto Lunar X prize contender Moonraker, which will explore the Lacus Mortis pit "skylight" and then lower its two wheeled rover Tetris into the pit . For details of this mission, see Robotic missions to the Moon, already planned, or near future, from 2017 onwards, below.

See also Lunar caves as a site for a lunar base

VOLATILE RESOURCES - INCLUDING ICE

We have pretty good evidence now of ice at the poles, in permanently shadowed craters, thought to be relatively pure and at least a couple of meters thick according to radar data from a NASA instrument flying on India's Chandrayaan-1 lunar orbiter.

It's not a direct detection however, so there is still room for skepticism about it, as rough material would have the same radar signature as radar transparent ice. But craters that are rough when new, are rough both inside and outside the crater rim. While these signatures are found only inside the craters and not outside the rims, which they interpret as meaning that they are caused by ice. The temperatures are also right for ice.

If it is ice, it could be "fluffy ice".

"We do not know the physical characteristics of this ice—solid, dense ice, or “fairy castle”—snow-like ice would have similar radar properties. In possible support of the latter, the low radar albedo and lower than typical CPR values for nonanomalous terrain near the polar craters are 0.2–0.3, somewhat lower than normal for the nonpolar highlands terrain of the Moon and are suggesting the presence of a low density, “fluffy” surface."

(page 13 of Evidence for water ice on the moon: Results for anomalous polar)

In either case, it is not just a little ice; if this is what they detected, there's estimated to be at least 600 million metric tons of this, and possibly much more.

It also contains other volatiles. We know for sure that there is some ice on the Moon, by the LCROSS impact experiment. Relative to H 2 O at 100% they found H 2 S at 16.75%, NH 3 at 6.03% SO 2 at 3.19%, C 2 H 4 at 3.12%, CO 2 at 2.17%.

So, if the rest of the ice at the poles has a similar constitution to the impact site that's a lot of nitrogen (in the ammonia) and CO 2 on the Moon at the poles.



The green circles here surround craters at the lunar north pole thought to have layers of ice, with an estimated total of at least 600 million metric tons of water.

(0 degrees longitude at bottom)

On the other hand, caution is needed as this is not direct detection. The LEND results (searching for hydrogen through reduced emissions of neutrons of a particular type) are particularly puzzling, as there is almost no resemblance between their map and the miniSAR map.

LEND map - in this picture blue is reduced neutron emission and shows likely locations of hydrogen. 0 degrees longitude is at the top.

They did detect hydrogen, but puzzlingly, it was not correlated with the permanently shadowed regions - there was some hydrogen in permanently shadowed regions, and some also in illuminated regions. A recent paper suggests that ice mixed in the regolith in illuminated regions may be ancient ice that survived a minor shift of the lunar axis. According to one hypothesis, this may be ancient deposits from over three billion years ago before volcanic activity, which changed the polar axis slightly by shifting material.

A new LEND mission has been proposed involving low passes over the poles at altitudes as low as a few kilometers, for higher resolution results.

The Moon may also have ice at lower latitudes too, as there are permanently shaded regions up to 58 degrees from the poles (only 32 degrees from the equator). Though these regions are too warm to have ice on the surface, there may be ice there underground. See Ice may lurk in shadows beyond Moon's poles (Nature, 2012).

At any rate, the Moon does seem to have resources of ice at the poles (though memorably, Patrick Moore in one of the last Sky at Night programs that he did said that he'd believe there is ice at the poles when someone brought him a glass of water from the Moon). More research is needed to find out how much there is and where it is.

Some scientists - particularly Arlin Crotts, think it may have ice several meters below the surface over the entire planet, and that it may have volatile resources deep down. There are signs that suggest it is still geologically active, and one possibility is that the activity may be due to volatiles deep down escaping to the surface. For more on this, see Geologically active moon

METALS

Critics often say that the Moon is undifferentiated and doesn't have any processes to concentrate ores. Although the Moon doesn't have any liquid water so all the processes involving concentration of resources through water erosion won't work, it still has many processes that can concentrate ores. Including:

Fractional crystallization - as a melt cools down, some minerals crystallize out at a higher temperature than others so form first. They then settle or float, so remove the chemical components that make them up from the mix, so changing its formula, leading to new crystals to form in a sequence.

- as a melt cools down, some minerals crystallize out at a higher temperature than others so form first. They then settle or float, so remove the chemical components that make them up from the mix, so changing its formula, leading to new crystals to form in a sequence. Gravitational settling , lower mass material floats to the top.

, lower mass material floats to the top. Volcanic outgassing can concentrate materials such as iron, sulfur, chlorine, zinc, cadmium, gold, silver and lead.

can concentrate materials such as iron, sulfur, chlorine, zinc, cadmium, gold, silver and lead. The processes that lead to volatiles condensing at the poles - which it seems can also concentrate silver too

- which it seems can also concentrate silver too Processes unique to the Moo n (perhaps electrostatic dust levitation may concentrate materials)?

n (perhaps electrostatic dust levitation may concentrate materials)? Volatiles brought in as part of the solar wind

Asteroid and micrometeorite impacts bring materials from asteroids to the lunar surface such as iron and possibly platinum group metals etc.

The Moon has many valuable ores for metals. For instance, the highland regions (probably the original crust of the Moon) consists mainly of Anorthite (a form of feldspar, formula CaAl 2 Si 2 O 8 ) which is 20% Aluminium, compared with 25% Aluminium for Bauxite on Earth. So aluminium ores are abundant on the Moon, indeed orders of magnitude more abundant than they are in typical asteroids, but it does require a lot of energy to extract the aluminium from the ore. Either a nuclear power plant or large areas of solar panels. Crawford, in his "Lunar Resources: a Review" * , says this about aluminium on the Moon:

"Aluminium (Al) is another potentially useful metal, with a concentration in lunar highland regoliths (typically10-18 wt%) that is orders of magnitude higher than occurs in likely asteroidal sources (i.e. ~1 wt% in carbonaceous and ordinary chondtites, and <0.01 wt% in iron meteorites; . It follows that, as for Ti, the Moon may become the preferred source for Al in cis-lunar space. Extraction of Al will require breaking down anorthitic plagioclase (CaAl2Si2O8), which is ubiquitous in the lunar highlands, but this will be energy intensive (e.g. via magma electrolysis or carbothermal reduction; Alternative, possibly less energy intensive, processes include the fluoridation process proposed by Landis , acid digestion of regolith to produce pure oxides followed by reduction of Al2O3 (Duke et al.), or a variant of the molten salt electrochemical process described by Schwandt et al."

Mining this for the aluminium would create calcium as a byproduct, which is useful as a conductor in vacuum conditions, a better conductor than copper weight for weight - you need half the mass for the same amount of electricity. (Copper does better than calcium on a per volume basis because it is 5.8 times denser, it is also of course much more practical in an atmosphere because calcium reacts vigorously with air, but that's not a problem for conductors that operate in a lunar vacuum, and in space applications the reduced mass may be an advantage).

"Calcium metal is not used as a conductor on Earth simply because calcium burns spontaneously when it comes in contact with oxygen (much like the pure magnesium metal in camera flashbulbs). But in vacuum environments in space, calcium becomes attractive. "Calcium is a better electrical conductor than both aluminum and copper. Calcium's conductivity also holds up better against heating. A couple of figures mining engineer David Kuck pulled out of the scientific literature: "At [20C, 68F], calcium will conduct 16.7% more electricity than aluminum, and at [100C, 212F] it will conduct 21.6% more electricity through one centimeter length and one gram mass of the respective metal." Compared to copper, calcium will conduct two and a half times as much electricity at 20C, 68F, and 297% as much at 100C, 212F. "Like copper, calcium metal is easy to work with. It is easily shaped and molded, machined, extruded into wire, pressed, and hammered. "As would be expected of a highland element, calcium is lightweight, roughly half the density of aluminum. However, calcium is not a good construction material because it is not strong. Calcium also sublimes (evaporates) slowly in vacuum, so it may be necessary to coat calcium parts to prevent the calcium from slowly coating other important surfaces like mirrors. In fact, calcium is sometimes used to deoxidize some metal surfaces. Calcium doesn't melt until 845C (1553F). "Utilization of lunar materials will see the introduction of industrial applications of calcium metal in space."



From the section on Mining the Moon in Permanent - by Mark Evan Prado, a physicist in the Washington, D.C., region working for the Pentagon in advanced planning in the space program.

The Moon is deficient in copper, at least on the basis of what is known so far, but as well as calcium, aluminium is a good conductor.

The LCROSS experiment found silver (a superb conductor) and mercury at the impact site, but the concentration is not known, except that it is far higher than the levels in the Apollo samples, and is probably in a layer below the surface, as the signal was delayed. See LCROSS mission may have struck silver on the moon.

It has abundant iron. In addition to ores (which would need a lot of power to extract), it actually has free (unoxidized) iron metal (see section 5, Metals from Crawford)" * . Some of this is nanophase iron mixed in with glass, and hard to extract, but some of it consists of small particles of iron (less than a micron in diameter) mixed in with the regolith, and it may be possible to extract it with magnets. I will go into this in more detail in the next section.

Mars doesn't have any free iron except for the occasional rare iron meteorites.

The iron is valuable for steel, and is also a conductor, though not nearly as good as Aluminium or Calcium. It would be useful for some applications such as electric railroads on Mars, and is a conductor easy to access in the early stages.

However it also contains a fair amount of nickel. Nickel and iron are useful for making nickel / iron batteries. These could be useful for making batteries on the Moon with in situ resources, for instance to help last through the lunar night.

"Iron-nickel batteries are very rugged. Their lifetimes which can exceed 20 years are not affected by heat, cold or deep cycling. They are not easily damaged by rapid discharging or over-charging. On the downside, they have poor performance at low temperatures but they can be kept warm with insulation (e.g. simple regolith) and thermal wadis. Also, they only have a charge to discharge efficiency of 65% and will self discharge at the rate of 20% to 40% per month. Despite these shortcomings, they might be the Moon-made power storage systems of choice due to their simplicity and the availability of their component materials on the Moon. Moreover, these materials are among the easiest of materials to produce on the Moon."

See Electrical Energy Storage Using Only Lunar Materials.

Then, you also have titanium. This is especially interesting as it is rare in asteroids. Apollo 17 samples are 20% high purity Ilmenite, a Titanium ore which is found in the lunar mare. And better than that, the Lunar Reconnaissance Orbiter, with its spectral mapping of the Moon, discovered deposits that are up to 10% titanium, more than ten times higher than titanium ores on Earth. (Phys.org report, NASA image). Titanium is an industrially desirable metal, stronger per unit weight than Aluminium (though it is a poor conductor).

Titanium is also widely used in medicine for hip replacements, dental implants, etc., as "one of the few metals human bone can grow around firmly", see also this new titanium / gold alloy four times tougher than titanium

Titanium is especially useful for medical applications because it

Forms an inert and stable titanium oxide layer spontaneously

Has a high strength to weight ratio

Doesn't leach into blood and other aqueous environments because of its low rate of ion formation

Is one of the few materials that can integrate directly into living bone tissues (osseointegration) without any soft tissue layers in between

Crawford writes (page 17)" * :

"Therefore, in the context of a future space economy, the Moon may have a significant advantage over asteroids as a source of Ti. The fact that oxygen is also produced as a result of Ti production from ilmenite could make combined Ti/O2 production one of the more economically attractive future industries on the Moon.

For more on this, see major lunar minerals. And for an in depth study, read Crawford's review" * .

So, yes, there are plenty of metals on the Moon, but it might take a lot of power to extract them, apart from the iron, if that can be separated out using magnets.And that's mainly based on the Apollo results which explored a small region of the lunar surface which has been found to be in some ways unrepresentative. The Moon may have many other surprises in store.

Many ores on Earth would not be detected from orbit, and it seems the Moon has a fairly complex geology as well from the Apollo results and from the lunar mapping showing variation in concentrations of various metals.

Global map of iron oxide concentrations on the lunar surface, with the colours showing 2% increments from black (0%) to white (16%). (Source: NASA/Clementine) - The method used is described here (and briefly here).- and paper covering it in detail with an earlier version of the map here. What they did is to compare the light reflected at just two wavelengths 750 and 950 nm and also look at the effects of space weathering which darkens the soil so there are two things there - the ratio of the intensities and the intensity at 950 nm -and then by doing that they are able to work out the iron concentration at a particular point. Then to interpret this they used ground truth from the returned Apollo samples. It's rather indirect and only possible because of the Apollo ground truth. They also found similarly large variations in the thorium and potassium content. The big splodge on the second, far side image, is probably due to the large impactor that created the Aitken basin digging up materials from the lower crust and mantle that are likely to be richer in iron oxide.

As one example of one way the Moon could surprise us - Earth is often hit by iron meteorites, so the Moon should be also.

Dennis Wingo has hypothesized in his Moonrush book, that the Moon may also have valuable platinum group metals (ruthenium, rhodium, palladium, osmium, iridium, and platinum) which could be mined, the result of the impacts of these iron meteorites. Iron meteorites often have high concentrations of these metals, and gold also (which doesn't count as PGM).

Taking this further, there's a hypothesis by Wieczorek et al that magnetic anomalies on the Moon around the south pole Aitken basin may result from the remains of the metal core of a large 110 km diameter differentiated asteroid that hit the Moon to form the basin. If so, they could be useful sources for platinum, gold, etc.

From Wieczorek et al, the North and South poles are marked N and S. Notice the magnetic anomalies clustered around part of the rim of the South Pole Aitken Basin. This is thought to be the result of an impact by a 110 km diameter asteroid. Wieczorek et al hypothesize that the magnetic anomalies trace out the remains of the metal core of this asteroid. If so these could be rich ores, including iron, nickel, also platinum and other platinum group metals (gold, rhodium etc). See page 16 of Crawford's Lunar Resources: A Review *

Platinum is a particularly useful metal (the other PGM's have similar properties to platinum and are also useful). It is heavy, soft, malleable as gold and silver, easy to draw into wires, very unreactive, and has a high melting point. Out of gold, silver, platinum and copper, platinum is the densest and the hardest and the least reactive (the others are somewhat better in terms of electrical and thermal conductivity, and malleability, but it's not too bad at those either).

So, it's not just useful for catalytic converters, fuel cells, dental fillings and jewelry. We'd probably use it a fair bit in other ways too if it didn't cost so much.

The platinum group metals might be valuable enough to return to Earth from the Moon, just as suggested for the asteroids, depending on how easy they are to return. Of course, you can't just take the current market value of platinum, multiply by the amount of platinum available in a large meteorite - or on the Moon if Wingo and Wieczorek et al are right - and conclude that you'd get trillions of dollars by returning all that platinum to Earth and selling it here.

You need to fulfill a need or eventually nobody will buy it, and whatever you use it for it has to be worth the expense of returning to Earth. If it's just to replace copper, for instance, in wires, it wouldn't be worth returning unless you could reduce the transport cost back to Earth right down.

Dennis Wingo suggested in Moonrush that it could be worth exporting it to Earth for use for fuel cells, as an application that could be high value and yet need a lot of platinum.

The gold could be useful too, on the Moon at least. You don't normally think of gold as more decorative than useful but it is used a fair bit in electronics.

Also when gold is combined with the abundant titanium on the Moon you get Ti 3 Au, an alloy with 70% less wear, four times the hardness and increased biocompatibility compared with pure titanium (and twice as hard as titanium / silver and titanium copper alloys). It's also 70% less wear than titanium, lower friction and four times harder with a hardness of 800 HV in the Vickers hardness test. Density about the same as steel.

(density of titanium: 4.43 g/cc. using the atomic masses of gold and titanium, multiplying by (196.96657+3*47.867)/(4*47.867)*4.43 = 7.88 approx. By comparison, density of steel is 7.75 g / cc).

Crawford's paper focuses on its medical applications, you can alloy titanium with copper or silver, which are twice as hard as pure titanium, but this is four times as hard. It's also 70% more resistant to wear which will make it last longer and lead to less debris. And has excellent biocompatibility properties. But I wonder if it might also have lunar applications, with the hardness especially and resistance to wear.

Probably only the platinum group metals would be worth returning to Earth, unless the costs of transport back to Earth go down considerably (maybe through the use of Hoyt's cislunar tether transport system ). However, whether or not they are useful for Earth, they are well worth using on the lunar surface once you have industry there.

The Moon has some advantages over Mars for metals, such as the pure nanophase iron mixed in with the regolith, which can only exist in oxidized form on Mars except for rare metal meteorites.

Also, it's unlikely it will be commercially worthwhile to return metals from Mars while there are definite possibilities of returning metals from the Moon. See Exporting materials from the Moon for future suggested low cost methods for export from the Moon. For discussion of whether anything physical could be worth the expense of export from Mars, see Commercial value for Mars

POSSIBILITY OF EXTRACTING METALS FROM LUNAR REGOLITH

Crawford touches on the idea of extracting metals from the lunar regolith using magnetic sieving. There are practical difficulties to overcome, but if they could be, it might be the easiest way of all to extract metals from the Moon, especially if you choose sites with high concentrations of meteoritic iron

As we saw in the last sectio