When the ExoMars 2020 mission touches down on the Red Planet, it will most likely be at Oxia Planum. The ExoMars Landing Site Selection Working Group has announced that this flat area near the Martian equator was recommended for the ESA-Roscosmos rover and surface science platform because it provides the best chances for finding signs of life, balanced against the need for a safe landing zone.

Oxia Planum is the lead contender of two primary landing sites under consideration by the Working Group. The other area is Mawrth Vallis, and both are located only a few hundred kilometers apart in the same region located north of the equator and have an elevation of about 3,000 m (1.8 mi) below the Martian equivalent of "sea level."

According to ESA, the site dates back to the time when liquid water could exist on the surface of the Mars – about four billion years ago. It boasts one of the richest known clay deposits on the planet and there are numerous channels running from the southern highlands to the northern lowlands, exposing older and interesting geological deposits.

This is particularly important because the primary goals of the unmanned ExoMars mission is to make the first search for direct signs of life on Mars since the NASA Viking lander missions of the 1970s. This means that during its recent two-day meeting at the National Space Centre in Leicester, England, the Working Group had to find the sweet spot between scientific, engineering, and technical requirements, and is the latest in five years of detailed examination of up to eight candidates.

The Group had to find a site with a low enough elevation to provide enough atmosphere for the parachutes during descent, a choice of landing zones free of obstacles for landing and deployment, and a number of scientifically interesting areas within driving distance without too much in the way of steep slopes or loose debris.

ESA says Oxia Planum meets these requirements with its clay deposits, wet ancient history, and recently exposed deposits that includes ones that have been sealed by later volcanic activity, protecting them from only the most recent erosion and space radiation.

"With ExoMars we are on a quest to find biosignatures," says ESA's ExoMars 2020 project scientist Jorge Vago. "While both sites offer valuable scientific opportunities to explore ancient water-rich environments that could have been colonized by microorganisms, Oxia Planum received the majority of votes. An impressive amount of work has gone into characterizing 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."

ExoMars 2020 is slated to launch between July 25 and 13 August 2020 atop a Proton-M rocket from Baikonur, Kazakhstan for a landing on Mars on March 19, 2021. In the meantime, the latest landing site selection will undergo internal review by ESA and Roscosmos and an official confirmation in mid-2019.

Source: ESA

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