For thousands of years, humans have looked to the stars, wondering whether there are other lifeforms out there in the vastness of space, but it might be worth taking a look at some truly alien life here on Earth first.

Is there alien life out there past our own planet and, if so, what does it look like?

These are questions that are asked in the deep philosophical conversations among friends, as well as the labs of scientists and institutes like the Search for Extraterrestrial Intelligence (SETI).

The problem is that these two discussions relate to only one idea, which is that we are trying to find an intelligence that would be technologically-similar to our own, or far more advanced in many cases.

Within the observable universe, there are potentially 100bn Earth-like planets out there in the Milky Way alone, and maybe close to sextillion even further into the universe.

This might sound like the odds of finding life increase, but where and how do you begin to search for extraterrestrial life when it makes the old saying of a ‘needle in a haystack’ look like a walk in the park.

Also, what are we looking for when we search for alien life? Do we fall into the trap of trying to find ‘little green men’? Or do we start from the very beginning to find the building blocks of life?

What Comet 67p can tell us

For astrobiologists – whose job is to search out these building blocks of life – the 2014 landing of the craft Philae on Comet 67p was an event like no other, offering potential game-changing discoveries.

In the months that followed its landing, a team of international researchers created a computer simulation suggesting that micro-organisms containing anti-freeze salt could exist in frozen water beneath the comet’s black hydrocarbon crust.

More recently, the parent craft to Philae, Rosetta, returned numerous readings of amino acids like glycine, which form the basis of proteins, one of the key building blocks of life.

But how could micro-organisms exist in the vacuum of space with no sunlight bar the occasional heat from a passing star?

Well, there are billions of examples here on Earth.

Whether it’s in the depths of the Arctic ice or at the base of a boiling volcano, there are forms of minute life – dubbed extremophiles – that can withstand almost any challenge thrown its way.

Perhaps one of the best-known extremophiles is the tardigrade, or water bear as it’s more affectionately known, which was earlier this year found to have survived being frozen for 30 years.

Yet this is nothing compared to previous tests undertaken with tardigrades that have shown the extremophile is able to withstand a dousing of radiation.

Scientists also subjected specimens to the vacuum of space for 10 days, yet still they came out unscathed.

‘We have a whole planet full of planet-lets’

“We have a whole planet full of ‘planet-lets’ in extreme conditions on Earth that are relatively rare here, but might be representative of more average conditions on other planets and bodies in our solar system or even beyond on exoplanets,” said Penelope Boston, the latest director of NASA’s Astrobiology Institute (NAI).

The fact that basic forms of life like the tardigrade can exist in some of the most inhospitable environments both on and outside of Earth means that the notion of extraterrestrial life doesn’t seem that far-fetched.

While the tardigrade is not the only extremophile out there, the fact that such basic lifeforms could exist even in locations on Earth once thought completely inhospitable makes the idea that life could exist on comets or planets closer to our own seem not-so far-fetched.

“These places give us practice thinking about how at least our type of carbon-based life deals with temperature extremes, heavy metals, radiation, extreme dryness, saltiness, and other conditions that we might encounter on other planets where we are searching for life,” Boston said.

Life on Mars

Boston spoke at length in 2008 about the possibility of the tiniest life on Mars and many other potential solar-system-based candidates, like the moons Ganymede and Titan.

Now, in 2016, we have documented evidence that liquid water exists on Mars that may originate from vast underground salty aquifers, Martian ice or even condensation from the planet’s thin atmosphere.

“What exactly that likelihood is, numerically, is beyond us at the moment to figure out,” Boston adds. “But with each new mission [to Mars], and tantalising finding, the potential habitability of Mars appears to have increased. I think that we have greater confidence that the search for extant life is worth the effort.”

Our ability to scientifically measure samples of extra-terrestrial soil relies entirely on the robots we send to do this work, such as the Curiosity rover.

The only problem is that no matter how hard we try, these rovers are not ideal scientists as we can’t seem quite able to crack the ability to keep them from becoming contaminated with Earthly material.

According to Boston, the real hope now is finding a way of getting humans to test this material under laboratory conditions – whether that’s by sending us there, or sending samples back.

Preventing the spread of a space virus

“My own hopes for the next 20 years include returning actual samples from Mars that we can study for their geochemistry, mineralogy, and potential traces of life that they may contain.

“And finally, as a lifelong supporter of human missions to Mars and the moon, I anticipate that we will be much further along our path to that direct human exploration in 20 years than we are now. I hope to see all of this within my lifetime.”

So if we one day confirm the existence of alien microbial life and want to return it to Earth, what procedure is in place?

It might sound like a science fiction plot, but an alien microbe returned to Earth and accidentally released into the wild could have a devastating effect on our environment if uncontained.

Even after the Apollo 11 mission, NASA was terrified that the astronauts would return a moon pathogen, resulting in the crew having to be greeted by US President Richard Nixon while in a quarantine chamber.

While a moon virus was dismissed quickly by NASA, international legislation exists to prevent an alien outbreak on Earth.

The Outer Space Treaty ratified by the five major world powers in 1967 set in motion a plan to prevent space from becoming another battlefield, but also ensuring the protection of Earth from space itself.

As Boston explained, astrobiologists treat non-terrestrial samples with the same caution that you would treat dealing with a sample of the Ebola virus or other lethal pathogen, despite the unlikeliness of a major outbreak.

“Since we know that pathogens co-evolve with their hosts, the likelihood of the actual pathogenicity of alien microorganisms for us or other Earth life is vanishingly-slim,” she said. “The risk is tiny but the potential consequences could be huge and so a highly conservative stance is appropriate and also the internationally accepted norm.”

Keeping space safe from infection

Yet it’s also important that, in order for us to find life out there in the universe, the equipment and people we send out there do not lead to our own outbreak anywhere where life could exist.

A recent example is NASA’s OSIRIS-REx spacecraft, which plans to land on the asteroid Bennu in 2023 and return a sample of its frozen interior.

Immediately after the craft takes off in a few years’ time, heaters will begin burning off any water on the craft’s OSIRIS-REx Visible and Infrared Spectrometer (OVIRS) to prevent any such Earthly contamination.

So what’s likely in store for the next 20 years in terms of our ability to determine whether life – intelligent or otherwise – exists out there in the wider universe?

We can say for almost an absolute certainty that as a species we will not be capable of sending human-piloted craft to explore distant worlds within the next two decades, but existing and new generations of telescopes can provide us with huge amounts of scientific data.

The search for life continues on Earth

Having already seen the Kepler space telescope discover more than 2,000 exoplanets in our observable universe so far, nations like China are now investing hundreds of millions of dollars in space telescope built to hunt for extra-terrestrial life.

The most recent of which being the 500-metre FAST telescope, the largest radio telescope ever built, making it capable of scanning the faintest of galaxies that many current Earth-based telescopes can only dream of.

Predicting what will come in the decades to come, Boston has, quite fittingly, used a natural metaphor, describing the galaxy as “opening up before us like a gigantic flower with thousands of exoplanet petals for us to study and scrutinise for clues about possible biospheres.

“As a lifelong supporter of human missions to Mars and the moon, I anticipate that we will be much further along our path to that direct human exploration in 20 years than we are now. I hope to see all of this within my lifetime.”