It seems likely that in next few decades we will find life or evidence that there was once life on Mars. The impact on humanity is easy to overstate, though it will certainly be significant, it will not change how we go about our daily lives a great deal, other than enrich the conversations we have. What it will do is help us understand the mechanisms for life, and how it starts, and give us the realisation that we are not unique. Mars could be a future home for humanity but we might want to be careful how we go about it.
Why do we think that we will find evidence of life at some point in Mars’ history? There are a number of plausible scenarios that indicate that life may have had a pretty good chance at starting on the red planet, most likely in its deep history within the first billion years. Like all reasonably sized celestial bodies, Mars underwent a process of differentiation where the heavy iron settled in the core and the lighter elements were more prevalent towards the crust. Mars, like the Earth, probably had a molten outer core that acted like a dynamo to generate a magnetic field. This magnetic field protected the planet from the harsh solar wind, which would have been greater than what we experience now. Without this protection the Martian atmosphere would have been stripped away from the planet very quickly.
Life on Mars
The atmosphere on the early planet would have been significantly thicker than it is now and the pressure would have been enough to enable water to be in liquid form on the surface. In these early years of the planet there would have been a lot of volcanic activity and if water was around on the surface then there would have been hot springs and other geothermal environments that we find so conducive for life here on Earth. On Earth we find mats of single celled organisms in these environment and it is not a great stretch of the imagine to consider that the environmental conditions on Mars may have been very similar, the only difference is that we have yet to find evidence of this.
Then it all went quiet
To keep an atmosphere you need enough gravity to make sure the escape velocity of molecules is sufficiently high that they do not easily escape. This is where Mars lucked out in the planetary mass stakes. With only 0.38 the gravity of Earth it doesn’t take a lot of excitement for molecules found in the atmosphere to reach a velocity where they can escape Mars’ meagre gravitational pull. Mars is a little over half the diameter of the Earth and only 10% of the mass with a similar rotation period. Though the outer molten core may well have set up a dynamo effect that created a magnetic field the small planet would have cooled quickly with radioactive heating not producing enough heat to keep the molten outer core churning. Slowly the magnetic field would have weakened to a point where the Sun’s solar wind would have eroded the atmosphere at a faster rate than it could be replenished.
What would have happened to the life?
The reducing pressure would have had two main effects that may have impacted any life on the red planet. Water would freeze as the temperature lowered and any ice that was on the surface would have sublimated straight into water vapour, due to the lowering pressure, waiting to be stripped from the atmosphere by the solar wind. For any chance of survival, microbial life would have had to seek shelter underground. The good news is the changes would have been very slow, well within the evolutionary ability of life to adapt to the changing environment. There would come a point though, where the conditions would simply become too hostile for life to survive at all, the pressure would be too meagre and the temperature too low and the solar radiation hitting the unprotected planet too high. So though life may have once flourished on the surface, it faced a slow demise deep within the Martian crust.
What about now?
It seems plausible that if there was once life on Mars there would be some evidence of it around features that have an analog to places here on Earth. One of the most promising environments is those around hot springs and scientists involved in the selection of where the Mars 2020 rover would land were proposing sites that showed features similar to long dead hot springs on Earth. What was ultimately selected as the landing site was an ancient estuary flowing into a lake held by a large crater. The theory being that a long since gone water course would bring evidence of life flowing down its channel and deposit this in the sediment on the lake. Given that the next few rovers that are planned to go to Mars won’t be doing very deep drilling it is unlikely that any existing life, that could be deeply buried in the Martian surface, would be found. What is more likely to be found is evidence that life was once on the red planet.
What would it mean to find evidence of past life on the red planet?
Currently we have only one example of life in the universe and that is on our planet Earth. If we were to find evidence of life in the past on Mars it would mean that life is not unique to one location in the universe. It may mean that life is unique to two locations, or it might mean that life is abundant throughout the solar system, the galaxy and the universe. Just to be clear, this doesn’t mean intelligent life, this means life in its most simplest form, after all life on Earth has spent most of its existence as single cell microbes. Fundamentally it would mean that we are not unique.
How would we cope with this information?
Some sectors of humanity would find the existence of life, albeit in the deep past, elsewhere in the universe somewhat confronting. Most people, though, would find it something that causes a pause for thought but little else than that moment of reflection. Governments won’t fall, society won’t rebel, religions won’t crumble, but we might take a little more time to think about our plans for Mars. We might consider that Mars would be better off being a reserve that humans just keep away from. Elon Musk might be compelled to rethink his efforts to establish a human colony on Mars, and redirect his efforts to something a little less damaging. If there is a chance that the evidence of life on Mars, in the past, points towards a fragile ecosystem deep within Martian soil then we would need to be very careful that we don’t disrupt it.
Without a doubt it would be the biggest news story of the century to confirm that life had existed somewhere other than the Earth. But that initial excitement would give way to the cold realities of day to day life on Earth. With any luck we might think a little more carefully about the footprint we would put on Mars, and maybe just leave tire tracks instead of footprints.