By Ryan Ridden 20/03/2016

Are we alone? This is one of the most profound questions we can and have asked. The quest to find life outside of Earth captures our attention. It is a quest that challenges how we view ourselves in the universe. Could it be that Earth is special and life thrives only here? Could it be that we, as a species are the only “intelligent beings” in the Universe? Or is the Earth just one alcove that life has taken hold and could it be that we are just one spot of intelligence in a sea awash with it?

Being the curious and social creatures that we are, it’s no surprise that we are drawn to this immense question. The search for life has plagued humanity’s mind for a long time, but only in the past few decades did we truly begin that search and in the decades to come we may have an answer.


Life on Mars

The great canal network Lowell believed he saw on Mars.
The great canal network Lowell believed he saw on Mars.

In the search of alien life Mars has been a focus point. Mars attracted most of our attention because it is relatively close by and it has a solid surface instruments can survive on. Interest with Martian life started in the 19th century with the not so accurate observations and imaginings of Percival Lowell. On Mars, Lowell saw a vast canal network, which he imagined was created by a civilisation threatened by catastrophic climate change—the Martians final engineering effort to stave off extinction. This tragic tale of a doomed civilisation, unfortunately only existed in Lowell’s mind, but it does mark the start of our search for life on Mars.

Since the time of Lowell we have learnt a great deal. The surface of Mars has been mapped by orbiting satellites and interrogated by a succession of landers and rovers. With these missions we tried to understand the mystery of Mars, to uncover its ancient history.  While we learnt about the world, the question ever lingered: is there life on Mars? Or could there have been life in the past?

More recently we have learnt a great deal about Mars’ history. Thanks to the rover Curiosity, we now know Mars once had running water. So Mars must have been similar to Earth, once upon a time. Mars had flowing water and it had strong volcanic activity, so perhaps it could have had life. A major part of Curiosity’s mission is to look for fossilised life in the Martian strata going up Mt. Sharp.

But these missions and discoveries look to the past, is there any evidence for life alive now on Mars?


Viking lander
Model of a Viking lander. Two of these landers were sent to Mars in 1967.

In 1976 a billion dollar mission landed on Mars. What landed on Mars were the two Viking landers, the most ambitious robotic laboratories of the time. These Vikings peacefully photographed their surroundings, examined the soil and looked for microbial life—they hunted for bacteria on Mars! Three experiments were used to hunt life, and astonishingly one of the experiments had a positive result. But that’s only one out of three.

The data from the Vikings were meticulously analysed and the conclusions strongly debated. This decision was about the discovery of alien life, which is pretty high stakes. It was crucial scientists came to the right conclusion. In the end it was decided that the one positive result was thanks to chemistry in the red soil and not life. The result itself may be a bit disappointing, but the discussion brought up a new and interesting questions; did we detect Martian life or hitchhikers from Earth?


Hitchhikers guide to panspermia

The idea that Earth life could have been carried to Mars unwittingly isn’t crazy, its panspermia. It’s just like sailing ships carrying stowaway rats from one island to another, something which New Zealanders are familiar with. The real challenge with panspermia is that we need to worry about stowaway bacteria, things tens of thousands of times smaller than rats. So how are spacecraft checked for micro-rats?

There are a few stages of sterilisation. Spacecraft that will spend their lives in space often have no treatment, relying on the fact they won’t ever touch a planet. For landers and rovers, more stringent sterilisation occur, but it’s not perfect. For some time it was assumed that nothing could survive the dangers of space and if any microbes got through sterilisation space would take care of it. It seems like a pretty safe bet, space is dangerous, there is no air, no water, it’s extremely cold and there is an enormous amount of radiation. So surely no bacteria will survive a trip through space.

The trouble is, the more we study simple life, like bacteria, the tougher we find it can be. In the past few decades, researchers have been amazed by incredibly tough bacteria known as extremophiles. Turning the idea that life is incredibly delicate on to its head, extremophiles thrive in extreme conditions. What’s more it almost seems like there is an extremophile for every situation, there are thermophiles which love hot places like hot pools and volcanic vents; xerophiles which thrive in extremely dry conditions and radioresistants which don’t mind high levels of radiation, happily living next to nuclear reactors.

The incredible ability of extremophiles to survive, has allowed life to live everywhere, from Earth’s surface to deep within its crust. There are also some larger critters which can survive in space, most notably the tardigrade, which has a reputation for being an ultimate survivor.  If an extremophile could survive the harsh conditions of space it could well be sent on an interplanetary voyage (by us) to colonise a new world—panspermia in action.

Tersicoccus phoenicis
Tersicoccus phoenicis, the bacteria which has only been found in spacecraft assembly clean rooms.

The risk of panspermia isn’t ignored and as I mentioned before there are sanitation precautions for lander spacecraft. The trouble with bacteria is that only one needs to survive. If all but one bacterium is killed off, that one can quickly divide and re-establish a colony to explore space. It gets even harder to make sure that the lander is sterilised thanks to a strain of bacteria called “Tersicoccus phoenicis”. This bacteria is an extremophile of sorts and has only be found twice, both times in spacecraft clean rooms.

Resilient to all conventional cleaning techniques tersicoccus phoenicis has hitched a ride on every spacecraft sent from Earth. At the moment we don’t know if it could survive in space, but if it can then tersicoccus phoenicis has made it to Venus, Mars and to the thick atmosphere of Jupiter. If even just one bacterium made it to a planet and liked the weather, there would now be an outpost of Earth life thriving on another world. Tersicoccus phoenicis could be an interplanetary species.

With all our technology bacteria may have beaten us in becoming Earth’s first interplanetary life!

Through the shear tenacity of bacteria, we might not be able to find the Martians through the Earth bacteria. Thankfully no landers have visited some of the nicer places on Mars where Martian life might still live. Mars as a whole is a pretty nasty place that Earth life could have a hard time living in, but there are other places in the solar system life could thrive.


A sea of possibility

Europa crosssection
Cross section of Jupiter’s moon Europa.With a thick ice sheet covering a global ocean this moon may be the best place to find alien life.

Out there orbiting the giant Jupiter is Europa, a moon which may be our best chance to find alien life. Europa is an incredible place, it has a thick icy surface which protects the inner global salty ocean from harmful radiation. This water moon is heated by a tidal tug of war between Jupiter and the other large moons, which keeps the interior liquid.

Life could exist in the ocean of Europa. It has everything we think life needs, which makes it an incredibly difficult environment for us not to contaminate. If we took hitchhiking bacteria to the oceans of Europa it may easily flourish, so we have to be incredibly careful. There would be no room for error.

Our understanding of Europa is set to change in the 2020s when NASA’s Europa mission launches. This mission will study Europa from orbit to examine the surface in great detail and potentially fly through a water plume, created by massive geysers on Europa. This mission will give us the best possible understanding of the moon short of swimming in its oceans, which is both technically difficult and dangerous.


Finding the answer

Finding alien life would be the greatest discovery made. It would tell us that we aren’t alone in the universe and shed light onto how life begun, but we must be careful to make sure it is alien life we find. Currently we don’t know how to guarantee that our landers are clean from any bacteria and we don’t know if our craft have already seeded other worlds with Earth life.

We may of course not find any life outside Earth in our solar system. If that is the case then we as a species could spread life to worlds where there is none, not unintentionally as we are now but purposefully.

Are we alone? Let’s find out.