Europe is going to look into a second site on Mars as a possible destination to send its 2021 rover. Scientists spent two days considering the options and plumped in the end for Mawrth Vallis – an area rich in clay minerals that must have formed during prolonged rock interactions with water. Mawrth joins Oxia Planum, which was chosen for study in 2015. The European Space Agency’s ExoMars rover will carry a suite of instruments to search for present or past life. It will use a drill to bore up to 2m into the ground, to find samples for analysis that have not been sterilized by the planet’s harsh environment.

The launch of the robot from Earth was due to take place in 2018 but this has now been pushed back by two years because of hold-ups in the preparation of hardware. Although unsatisfactory, the lagging has at least allowed scientists to consider in detail a wider selection of potential landing sites. Engineering constraints, including the angle of approach to the Red Planet, meant that only Oxia Planum was really suitable for a mission launched in 2018.

In July 2020, a launch brought back into play two sites of interest that had originally lost out to Oxia. Mawrth Vallis has long interested scientists. The terrain is ancient and there is a feeling that if life has ever existed on Mars, this might be the kind of area that would retain evidence of its presence. The other candidate, Aram Dorsum was on the table during the two days of analysis at ESA’s technical center in Noordwijk in the Netherlands. Aram contains a large channel. The sedimentary rocks around this channel may well be the consequence of flood deposits.

At the end, the Noordwijk meeting voted in favor of Mawrth, and this was then endorsed by the ExoMars Landing Site Selection Working Group (LSSWG). Technically, Oxia Planum, another clay-rich location was back in competition, but it remains in play and will now be subjected as ExoMars project scientist Jorge Vago put it to “excruciating investigation”, along with Mawrth. Picture analysts need to identify a swathe of ground roughly 120km by 20km at both locations that are largely free from fissures, larger boulders and excessive slopes.

These are the threats that could kill the rover before its surface mission has even begun. Assuming that can be done for both Mawrth Vallis and Oxia Planum, a final decision on where to send the robot can be made on the science imperatives alone. This down selection to the one preferred destination is not expected to be made until the year before launch.

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