For nearly a hundred years, Earth has sent radio signals into space. If anyone nearby is listening, they probably know we’re here. In light of this, a new paper assesses the potential danger presented by such signals, concluding that the benefits outweigh the risks. But how can we really know?


Top image: Scene from Battleship (2012), a film in which an alien civilization discovers Earth by detecting its radio emissions.

Leaky Earth?

We’ve been shouting out into the cosmos for quite some time now. Electromagnetic waves of various intensities and frequencies have been streaming away from Earth for well over a century, the remnants of TV broadcasts, mobile phone conversations, satellite transmissions, and military, civil and astronomical radars.


We’ve even deliberately tried to get ET’s attention — a controversial practice known as METI (Messaging to Extraterrestrial Intelligences). There have been many such attempts, including the 2001 Teen-Age Message to the Stars organized by the Russian cosmologist Alexander Zaitsev. His work, and those of others, have been criticized as being insanely risky given the dearth of information we have about the nature of ETIs. Two years ago, John Billingham and James Benford called for a global moratorium on METI, an initiative similar to the one David Brin and myself worked on last decade.

But now, owing to all this human activity, the Earth has a radiosphere that’s inexorably billowing outwards at the speed of light — a clear signal that’s just waiting to be picked up.

And indeed, according to the new paper’s authors, Jacob Haqq-Misra, Michael Busch, Sanjoy Som, and Seth Baum, this leakage could in fact be detected by an extraterrestrial intelligence (ETI) armed with the right listening equipment.

Our signals decrease in intensity as they leak out into the cosmos. But depending on the signal’s strength and frequency, these waves can propagate for cosmologically vast distances and still carry enough information to connote the presence of intelligent life.


Arecibo Observatory. Credit: H. Schweiker/WIYN and NOAO/AURA/NSF.

The Arecibo Planetary Radar in Puerto Rico provides a good example. As the researchers note, at a transmitting power of 0.8 MW and a frequency of 2,380 MHz, the APR’s powerful signal could be picked up by a “watcher” with a 1 km2 receiving antenna at distances of up to 200,000 light years!


Credit: Haqq-Misra et al.

That's a rather extraordinary claim, so I spoke to SETI expert and scifi novelist David Brin about it — and he's not convinced detection is this easy. He told me that, even if an ETI had a one square kilometer array, they would have to point it a at Earth for the duration of an entire year. "Because it would take that long," he told io9. "But why stare if you don't already have a reason to suspect?"


Like SETI Institute's Seth Shostak, Brin believes that Earth is not detectable beyond five light years.

"With one exception: Narrow-focused, coherent (laser-like) planetary radars that are aimed to briefly scan the surfaces of asteroids and moons," he says, "And not to be confused with military radars that disperse."


This new paper, says Brin, is very unconvincing about detectability of leakage.

To transmit or not to transmit?

Earth's leakiness aside, we also need to know if anyone out there is even listening.


As the authors note, some SETI experts contend that, if an ETI really wanted to know that we’re here, they could locate us without having to listen for our radio waves. For example, they could figure out that life is here by analyzing the spectrum of reflected ultraviolet, optical, and near-infrared sunlight from the Earth’s surface and atmosphere. Or, an ETI could learn of our technological civilization by detecting artificial nighttime lighting of large urban areas, or by detecting exaggerated amounts of carbon dioxide in the atmosphere.

More conceptually, advanced civs could could pepper the galaxy with Bracewell communication probes — a point the authors fail to mention in the paper; they could already be in the neighbourhood waiting for a particular signal.


There’s always the possibility, of course, that we’re too far away from the nearest ETI. Or that alien life is rare. Depending on how one fills in the Drake Equation, there could be anywhere from one (just us) to 100,000 — or even millions — of civs currently residing in the galaxy. But we just don’t know, so we don’t really have a good way of knowing how detectable we really are.


Furthermore, and as Brin pointed out to me, the authors failed to address the possibility of colonization. "If travel happens, then the number of sites skyrockets," he says.


Also, ETIs may be able to detect our signals, but they may not be able to make any sense of them — but this is unlikely. If an alien receives a METI signal, it would likely consist of easily decipherable mathematical concepts built upon a computational language (a la Carl Sagan’s Contact). Radio leakage, on the other hand, would be meaningless and almost completely devoid of context. But as the authors write:

Earth’s radio leakage and deliberate transmissions will likely be identifiable by ETI as a technological signature because no other examples of such signals exist in nature. The ability of ETI to decipher or interpret the content of a signal is therefore irrelevant to their ability to use it to learn that humans exist...


But assuming detection is not easy, and that there are other variables at play (like cosmologically vast distances and the potential for many short-lived civilizations), we still need to ask whether or not humanity would benefit or face terrible consequences from alien contact.

To transmit or not to transmit

And indeed, as the authors note, a standard risk assessment is in fact warranted: We should evaluate the probability of an event occurring by multiplying the magnitude of the harm from that event if it does occur.


Sure — sounds sensible. But it’s difficult, if not impossible, to assess the magnitude of the harms that could come from ETI contact. We don’t know the nature of the interactions, nor do we know alien ethics (particularly from a super-technological machine-based civilization).

We also don’t know how we’d interact. The entire relationship could be conducted via remote messaging. But they could send us something rather nasty. At the same time, a positive, non-malicious message could really benefit us. An ETI could provide information about itself or its technologies which could advance and greatly influence the human condition.


Alien contact could also have positive and negative outcomes for many societal structures, religions, and philosophies; different human groups would be affected differently. Interstellar civilizational encounters could be similar to — if not considerably worse than — Europeans who made first contact with stone age societies.


There is another possibility — that the vast majority of our transmissions, and those of a civilization for that matter, will be detected long after we’re gone. Consequently, this is all a futile exercise. If the galaxy is littered with short-lived civilizations — a possible reconciliation of the annoying Fermi Paradox — all radio-transmitting ETIs are essentially sending “time capsule” messages or trace-signatures into space. The galaxy could be awash with echos from extinct civilizations. Determining civilizational longevity, therefore, is crucial to our assessment of the risks and benefits of transmitting into space.


Which brings up another interesting point: Maybe there’s value in transmitting a comprehensive “time-capsule” into space as a way of archiving or preserving our civilization’s vast history. If we go extinct, at least some other civilization may learn about us. Or more romantically, we’ll rest knowing that our signals are propagating through space long after we’re gone.

So, in response to the question of whether or not we should transmit, the authors write:

[B]ecause we cannot estimate the probability or magnitude of contact with ETI, we make no attempt to calculate the term. By extension, any conclusions that depend on knowing are conditional.


Which seems like a rather wishy-washy answer. The authors conclude that “the benefits of radio communication on Earth today outweigh any benefits or harms that could arise from contact with ETI.” What they mean is that it may be more important to our security and survival if we continue to develop powerful communications technologies; it’s simply too valuable (and disruptive) to give up.

But how can they possibly know for sure!? Brin referred to it as "arm-waving mumbo jumbo" — and an "utterly tendentious and unsupported claim."


In regards to METI, the authors conclude that current efforts, which are weak and mostly symbolic, are mostly harmless:

These transmissions create benefits such as opportunities for educational public outreach and the ability to develop scientific groundwork for future METI projects. The costs associated with METI at low levels of detectability are small, so such projects create overall positive value for humanity and should continue.


But ramping up the METI project, like creating powerful beacons, could result in highly uncertain outcomes. Mercifully, the authors conclude that governments and other agencies need to get their act together and start talking about it.

“Even if we never succeed in receiving a message from an extraterrestrial civilization, METI may still prove a worthwhile investment as a way to increase humanity’s awareness of itself in the greater cosmos.”


Unless, of course, someone is in fact listening, and they'd like to pay us a visit...

Read the entire study at Space Policy: “The Benefits and Harms of Transmitting Into Space.”