ESA to narrow down possible Mars landing sites in search for life

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This article titled “ESA to narrow down possible Mars landing sites in search for life” was written by Dr Peter Grindrod, for theguardian.com on Tuesday 28th March 2017 13.09 UTC

In about four years, the ExoMars rover will open its eyes on the surface of Mars. After a brief look around, its wheels will slowly crunch onto the frozen ground, beginning its journey on another planet.

Later today we should be one step closer to knowing where it will open its eyes. It has taken the last three years to narrow down the choice from eight, to four, to just three possible locations, each with their own unique selling points. And by the end of today the choice will be reduced to the final two sites.

One candidate site that I and others have spent a long time working on has made it to this late stage and we hope that it is interesting and safe enough to make it to the final.

The final three ExoMars landing sites (red stars) on a global elevation map of Mars. The ancient river channels marked in black mostly occur in the southern hemisphere, whereas the equally ancient but recently discovered inverted channels bridge a previous gap to the northern lowlands. Photograph: Data: Nasa/JPL/GSFC; Map: Peter Grindrod

As we prepared our case for the next workshop at the European Space Agency, my mind drifted towards what it could feel like to actually explore this area that we’ve come to know so well from orbit, but this time through the eyes and instruments of a rover.

It’s a site that I expect will be simultaneously familiar, and yet completely alien to us. River-worn pebbles could litter the ancient river channel, now a flat-topped ridge, but we’re hoping for finer rewards.

There are likely mudstones that we hope to drill, as we think that they could be good at preserving and even concentrating evidence of past, ancient microbial life — if it was ever present on Mars to begin with.

We’ve got some idea of what exploring an area like this will involve. Last year, a large group of scientists and engineers took part in a Mars rover trial, sending some of the ExoMars instruments out to the Utah desert to test both machine and people.

This endeavour was led by the UK Space Agency, but was carried out in parallel with teams from the Canadian, German and US space agencies. As it happens, the site chosen for all of these tests was one that is almost directly analogous to our site on Mars.

The landscape in this part of Utah has rather unusual geological features, at least for Earth. Rivers that dried up, turned to rock and were then buried have since been eroded back by the wind. Meanwhile, the softer floodplains on the river margins erode more easily, leaving an upstanding or inverted river channel. Such features are much more common on Mars.

Exploring an inverted channel on Earth has opened our eyes to the potential of a similar site on Mars. But doing the same for a rover on another planet comes with added pitfalls. How troubling is a little hill? The slopes can’t be too steep upon which to land or drive. The area has to be almost as flat as a mill pond, but rather harder one hopes.

What views will soon form the background scene of the ExoMars rover? Photograph: Esa/ATG medialab

As it happens, some of the best places for ExoMars to explore are actually very flat, having only been recently exposed by wind erosion, at least in geological terms. For example, we think the likely mudstones at our site have only been uncovered for a few hundred million years or so. This is a good thing, as with a thin atmosphere and no magnetic field for shielding, the surface of mars is bombarded with radiation from the sun and cosmic rays, which breaks down the organic chemistry that will be our evidence for life.

It is no trivial task to look for evidence of the earliest forms of life on Earth, even with repeated fieldwork and the latest laboratory techniques. But somewhat paradoxically, Mars might actually be an easier to place to find evidence of early life because it hasn’t gone through the same tumultuous plate tectonic activity as Earth, which metamorphoses and even destroys the oldest, life-bearing rocks. And it’s been a few billion years since Mars had a thick atmosphere and surface water altering the landscape. So the evidence could be well preserved.

The best chance of finding evidence of life elsewhere in the Solar System in the next couple of decades is with Mars. And if ExoMars finds a tantalising hint of life, then the case for bringing samples back to Earth will be even stronger. Because once in the laboratories of Earth, the great analytical precision will mean that we should have extraordinary evidence of an extraordinary claim.

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