Credit: @EPSC2012

EPSC 2015 – Mars

I’m fresh back from the European Planetary Science Congress in Nantes, France, which was a really excellent event this year. Not only did we hear a whole slew of new research findings, but, because it was run alongside an interactive exhibition about space exploration for the general public, we were constantly reminded that what we do is incredibly exciting!

The beginning of the conference (and particularly the Mars session) was overshadowed by the much-heralded NASA announcement: a new paper showing that seasonally-detected Recurring Slope Lineae (RSLs) are most likely formed by brines, indicating present-day surface water flow on Mars. There was a certain amount of eye-rolling at this (RSLs are well-known and this theory has been being put together for some years – check out my post from 2012), but the more constructive comments I heard were to the effect that other agencies have something to learn from NASA if they are capable of drumming up this kind of media storm over something that is essentially simply an incremental step in the story.

The proposed landing sites for the ExoMars 2018 rover (Image: ESA)

We also heard in detail about the 4 proposed landing sites for the ExoMars 2018 rover, due to be downselected to just 2 in a few weeks’ time. They’re all sites where ancient clays have been detected at the surface, and are thought to have the potential to retain evidence for past life on the planet. They do differ, though, in the safety with which a landing can be made, in the ancient environment in which the clays are thought to have formed, and in their geological complexity. These differences mean that deciding between them involves some hard choices, as outlined by John Carter (not that one!) For instance, is it better to choose a site that is unique and complex (i.e. Mawth Vallis), or somewhere more representative of wider Mars environments? And if two sites, such as Oxia Planum and Mawth Valles, have many elements in common, should we choose the safer one? Personally, I’d argue for a representative and safe site, but we’ll have to wait and see whether the selection panel agrees.

The Isidis impact basin (image: ESA)

The Mars science talks were wide-ranging and, at times, controversial. For example, Olivier Bourgeois showed how his thermomechanical modelling, along with previous mapping work, indicates that there was once a massive wet-based ice sheet within the giant Isidis impact basin. How, then, asked Ernst Hauber, could the small volcanic cones observed on the basin floor form? Bourgeois responded that these are not volcanic, but are glacial and post-glacial. As so often for Mars, it’s difficult to decide between a water-related and a volcanic genesis for landforms we have only observed from orbit, and it will not be easy to reach a consensus. If only the much-lamented Beagle 2 rover had survived to roam the Isidis plains!

We also heard new work shedding light on gullies, another recent landform (besides RSLs) that could indicate the action of liquid water at Mars’ surface today. Mathieu Vincendon presented evidence that presently-active gullies are most heavily modified in the part of the year when CO2 ice is stable on the slopes where they form. This could mean CO2 ice is involved in their formation, or it could be the combined volume of H2O and CO2 ice at that time that results in this higher level of slope modification. Certainly, there is some minor activity in the period when only H2O is stable, so it doesn’t look like we should be looking to CO2 as the sole agent of gully-formation. We also heard compelling arguments from Tjalling van Haas that gullies form by debris flows, so perhaps we are inching towards the truth behind these much-discussed landforms.

Overall, the Mars sessions were fascinating and varied. With so much high-resolution, high-quality data being accumulated on the planet, we’re getting ever-better answers to the burning questions about our next-door neighbour. This is also an exciting time for first-looks at smaller bodies, in particular Rosetta’s target comet, 67P, and the dwarf planet Ceres. The new data coming from these missions has everyone all fired up, so that will be the topic of my next post.