Scientists with the European Space Agency's ExoMars mission have picked Oxia Planum as their top site to land a rover that will look for past or present day life on Mars.
Data collected by orbiting spacecraft show Oxia Planum, located near Mars' equatorial region, is laced with tantalizing chemical fingerprints of clays and other minerals that form when rock interacts with water. Scientists estimate the region is about 3.9 billion years old, a time when Mars was believed to be warmer and much wetter than it appears today.
Life, if it ever existed, is expected to be challenging to find on Mars because the planet's thin atmosphere offers little protection from cosmic and solar ultraviolet radiation. Also, the same processes that form rock, tend to destroy organic molecules.
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Mars also is covered with potentially toxic salts, know as perchlorates, which complicates not only the search for life, but the techniques used to look for organics.
Oxia Planum, however, shows signs of past volcanic activity, so scientists are hopeful some deposits containing organic material may have been covered in lava and preserved. Relatively recent erosion then may have made some of those deposits accessible.
The ExoMars rover is scheduled to launch in 2018, though a recently discovered technical issue may delay the flight to 2020. The rover will be outfitted with a drill that can extract samples from about 6.5 feet, or 2 meters, beneath the surface. Onboard instruments will then search samples for molecular biosignatures.
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Scientists made detailed evaluations of three other sites - Aram Doraum, Hypanis Vallis, and Mawrth Vallis - but decided to focus on Oxia Planum after weighing a host of engineering and science factors.
For example, ExoMars needs to land on a relatively low-lying site so it can fly through as much of the Martian atmosphere as possible to slow itself for a parachute touchdown. Scientists also took into account forecasts of horizontal and vertical wind speeds during the descent, as the rover will land at the end of the 2019 global dust season.
The landing site evaluation team also had to avoid potential hazardous slopes and boulders.
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"Our preliminary analysis shows that Oxia Planum appears to satisfy the strict engineering constraints while also offering some very interesting opportunities to study, in situ, places where biosignatures might best be preserved," ESA project scientist Jorge Vago said in a statement.
ESA and Roscosmos, the Russian Space Agency, which is a partner in the project, will make a final call on the ExoMars landing site six months before launch.