ExoMars landing site revealed

Oxia Planum favoured for mission to Mars

The landing site for the ExoMars (Exobiology on Mars) mission to search for evidence of life on Mars was chosen earlier this month in a meeting organised by the University of Leicester’s Space Research Centre.

Over 100 delegates from the ExoMars Landing Site Selection Working Group gathered at the National Space Centre to make recommendations for the landing site. Oxia Planum was chosen as the site where the rover will land on the red planet in 2020.

ExoMars is a joint mission between the European Space Agency (ESA) and the Russian Space Agency (Roscosmos). The proposal of the group will be reviewed internally by ESA and Roscosmos with an official confirmation expected mid-2019.

Meeting organiser Professor John Bridges, Professor of Planetary Science at the University’s Space Research Centre said: “The University of Leicester and the UK space science community have a major stake in Mars exploration plans. 

“The ExoMars 2020 rover is an important part of that both from the point of view of science exploitation and also for technology development. Last week at the National Space Centre a group of 100 scientists and engineers decided that Oxia Planum was the best landing site for ExoMars – which is designed to drill and search for traces of ancient life. This is the culmination of five years of selection and characterisation of different potential sites.”

Professor Bridges added: “Future Mars exploration centres around Mars Sample Return, and this brings new challenges both on Mars – we need a fetch rover and spacecraft to bring samples back to Earth – and for analysis of returned samples under stringent planetary protection conditions.

“At the Space Research Centre, we are leading the development of new technologies for returned sample analyses and also preparing for MSR both by analysing martian meteorites and through being part of current Mars missions (Mars Science Laboratory, ExoMars, HiRISE onboard NASA’s Mars Reconnaissance Orbiter (MRO)).”

At the heart of the ExoMars programme is the quest to determine if life has ever existed on Mars, a planet that has clearly hosted water in the past, but has a dry surface exposed to harsh radiation today.

While the ExoMars Trace Gas Orbiter, launched in 2016, began its science mission earlier this year to search for tiny amounts of gases in the atmosphere that might be linked to biological or geological activity, the rover will drive to different locations and drill down to two metres below the surface in search of clues for past life preserved underground. It will relay its data to Earth through the Trace Gas Orbiter.

Both landing site candidates – Oxia Planum and Mawrth Vallis – preserve a rich record of geological history from the planet’s wetter past, approximately four billion years ago. They lie just north of the equator, with several hundred kilometres between them, in an area of the planet with many channels cutting through from the southern highlands to the northern lowlands. Since life as we know it on Earth requires liquid water, locations like these include many prime targets to search for clues that may help reveal the presence of past life on Mars.

Oxia Planum lies near the boundary where many channels emptied into the vast lowland plains. Observations from orbit show that the region exhibits layers of clay-rich minerals that were formed in wet conditions some four billion years ago, likely in a large body of standing water. The channels that transported material into the lower-elevation ‘sink’, where the landing ellipse is situated, cover an area of 212 000 square kilometres. Layers of material that have been recently exposed through erosion are accessible from any of the touchdown points, giving a window into the early history of this area.

The minerals in Oxia Planum are representative of those found in a wide area around the region and so would provide insight into the conditions experienced at a global scale, putting constraints on the climate and habitability potential of Mars in this period.

On the technical side, the landing site must be at a suitably low elevation level, so that there is sufficient atmosphere and time to help slow the landing module’s parachute descent. Then, the 120 x 19 km landing ellipses should not contain features that could endanger the landing, the deployment of the surface platform ramps for the rover to exit, and the subsequent driving of the rover. This means scrutinising the region for steep slopes, loose material and large rocks.

On the science side, the analysis had to identify sites where the rover could use its drill to retrieve samples from below the surface, and to define possible traverses it could make up to 5 km from its touchdown point in order to reach the maximum number of interesting locations.

ESA’s ExoMars 2020 project scientist Jorge Vago said: “With ExoMars we are on a quest to find biosignatures. While both sites offer valuable scientific opportunities to explore ancient water-rich environments that could have been colonised by micro-organisms, Oxia Planum received the majority of votes.

“An impressive amount of work has gone into characterising the proposed sites, demonstrating that they meet the scientific requirements for the goals of the ExoMars mission. Mawrth Vallis is a scientifically unique site, but Oxia Planum offers an additional safety margin for entry, descent and landing, and for traversing the terrain to reach the scientifically interesting sites that have been identified from orbit.”

The ESA-led rover and Roscosmos-led surface science platform will launch in the 25 July–13 August 2020 launch window on a Proton-M rocket from Baikonur, Kazakhstan, and cruise to Mars in a carrier module containing a single descent module, arriving at Mars March 2021.