The joint ESA-Roscosmos ExoMars mission has chosen an area called Oxia Planum as its favoured landing site to look for life, now or in the past.
There was heated scientific debate at the meeting in Leicester, UK, to decide which of the two finalilsts — Mawrth Vallis or Oxia Planum — would prevail.
The selection now has to be reviewed by the top brass at ESA and the Russian space agency Roscosmos before getting the full rubber stamp treatment in mid-2019.
ESA's Hakan Svedhem told Euronews what made Oxia Planum a top pick.
"Because of the variety of minerals there, and because of the old history, and all elements are there, we believe that possibly it could have been ingredients to life in the early Martian days, and there has been water in the past," he said.
"In addition, it is quite a safe place to go and land because we know the surface is safe for landing. It's located on a low level, so that the spacecraft has a lot of atmosphere to go down through and slow down, and has time to react and respond before it lands."
The ExoMars mission comes in two halves. The Trace Gas Orbiter spacecraft was launched in 2016 and is already circling Mars, sniffing its atmosphere for signs of life-linked molecules like methane, and then in 2020 the second mission launches with a European rover and a Russian surface science platform heading for Oxia.
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.
“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,” ESA’s ExoMars 2020 project scientist Jorge Vago said.
The recommendation was made today following a two-day meeting held at the National Space Centre in Leicester, UK, which saw experts from the Mars science community, industry, and ExoMars project present and discuss the scientific merits of the sites alongside the engineering and technical constraints.
The quest to find the perfect landing site began almost five years ago, in December 2013, when the science community was asked to propose candidate locations.
Eight proposals were considered in the following April, with four put forward for detailed analysis in late 2014.
In October 2015, Oxia Planum was identified as one of the most compatible sites with the mission requirements — at that time with a 2018 launch date in mind — with a second option to be selected from Aram Dorsum and Mawrth Vallis.
In March 2017, the down-selection identified Oxia Planum and Mawrth Vallis as the two candidates for the 2020 mission, with both undergoing a detailed evaluation over the last 18 months.
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.
Oxia Planum is interesting because it's at the boundary between different channels that emptied into lowland plains. There are clays there which formed in the presence of water long in the past.