The decision has been made ...
Oxia Planum is north and east of Valles Marineris and due north of Margaritifer Terra. The site contains one of the largest exposures of rocks believed to be one of the earliest in Mars history - around 3.9 billion years old.
The ExoMars Program
The ExoMars 2018 mission will consist of a rover and surface platform and is the second of two missions making up the ExoMars program. Launch is planned for May 2018, with touchdown on the Red Planet in January 2019.
But before this mission is launched, ExoMars will send their first probes in 2016.
The Trace Gas Orbiter and the Schiaparelli entry, descent and landing demonstrator module will be launched in March 2016 and will arrive at Mars about a year later. Schiaparelli will land in Meridiani Planum. The orbiter will study the atmosphere and act as a relay for the second mission.
Data from this first mission will be used to finalize the mars landing site for ExoMars 2018, but the announcement made this week states that, for now, Ocia Planum is the preferred choice
Selecting a Mars Landing Site
The search for a suitable Mars landing site began in December 2013, when the science community was asked to propose candidates. In October 2014, the Landing Site Selection Working Group chose four sites. The last year has been spent evaluating these four sites by not only debating which site will have the best scientific return, but also the technical and egnineering risks associated with descent and landing.
Once on the surface, the main goal of the rover will be to search for evidence of martian life, past or present, in an area with some of the oldest rocks and mars and where liquid water was once abundant. A drill capable of extracting samples from up to 2 m below the surface will be included in the science package, which is crucial. . The present surface of Mars is a hostile place for living organisms and, by searching underground, the rover has more chance of succeeding in finding evidence of life..
Scientists believe that primitive life could have gained a foothold when the surface of Mars was much wetter, perhaps around 3.6 billion years ago. And buried or recently exposed sedimentary deposits offer the best chance to explore this period of Mars history.
All four sites under study - Aram Dorsum, Hypanis Vallis, Mawrth Vallis and Oxia Planum - show evidence of having water in the past, and are likely representative of global processes operating in the Red Planet's early history.
Each site also has a landing site with numerous targets that are scientifically interesting right at the Mars landing site, or within a 2 kilometer traverse over the planned 218 sol mission.
Note: 1 sol (martian day) is about 24 hours and 39 minutes long. 218 sols would be the equivalent of about 224 earth days.
The sites must also meet strict engineering constraints for entry, descent and landing. Low lying sites are considered the most accessible because they give the entry capsule more atmosphere in which to slow down and use parachutes.
Wind speeds expected during the descent must also be also considered - ExoMars 2018 will land at the end of the planet's global dust storm season in 2019.
Taking into account these requirements and the arguments that were made for each site, the Landing Site Selection Working Group recommended that Oxia Planum be the primary focus for the 2018 mission.
A further recommendation was made to also consider Oxia Planum as one of the two candidate landing sites for the backup launch opportunity in 2020, with a second to be selected from Aram Dorsum and Mawrth Vallis.
As Jorge Vago, ESA's project scientist, stated:
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.
Oxia Planum contains one of the largest exposures of rocks on Mars that are around 3.9 billion years old and clay-rich, indicating that water once played a role here. The area also has a wide area of valleys lined with exposed rock of varying types -- a good indication of different multiple episodes of water and deposition.
It appears a period of volcanic activity may also have covered the early deposits, which means that signs of life may very well be preserved underneath the surface and protected against the harsh radiation.
Overall, it appears to be a very good choice for the ExoMars 2018 Mars landing site.
Compared with landing site selection for previous missions, which relied primarily on the morphology of candidate sites alone, we are today in a much better position to understand the mineralogy of the various sites.
This puts us in the best position to choose sites that offer access to the most ancient, pristine material that not only preserves a record of early Mars but which is globally representative of processes occurring across the planet.
It made for a challenging decision, given the quality of the cases for all sites, but we are looking forward to the next stage of analysis as we move closer to the launch of our exciting mission: our rover will search for molecular biosignatures in the subsurface for the very first time.
Selection of the final Marrs landing site by ESA and Roscosmos is planned to occur six months before launch.
More information about the Landing Site Selection WorkingGgroup is available here.