Introduction

Before the end of this decade, the first European rover, part of the ExoMars 2020 mission, will land on Mars to search for signs of life! But where should it land ?

In December 2013, scientists were asked to propose scientifically compelling landing sites, that would allow for both the safe landing and operation of the rover.

Out of the eight landing sites proposed and discussed in April 2014, four candidates were selected for further analysis.

In March 2017, Oxia Planum and Mawrth Vallis were selected as final candidates.

Explore the map with the mouse, or use the bottom navigation controls to follow a story explaining the main landing site selection constraints, and letting you explore each candidate at high-resolution.

Elevation constraint

First, in order to have a successful landing, the elevation of the landing site must be lower than -2 km.

All landers use a parachute to slow down as they come through the thin atmosphere of Mars. To make sure that the parachute has enough time to do its job, the landers need to touch down at as low an elevation as possible.

On this altimetry map, derived from the Mars Orbiter Laser Altimeter (MOLA), areas ruled out for a safe landing are shown dimmed.

Latitude constraint

Next, because it is solar-powered, the ExoMars rover has to land in a latitude band straddling the equator between 5°S and 25°N.

Latitudes outside this range would cause either degraded electrical power or challenging thermal conditions for the rover.

Geological constraint

Most of the evidence that we’ve gathered in the last 40 years says that the earlier parts of Mars’ history were the most hospitable to life. Mars was certainly wetter, probably warmer, and had a much thicker atmosphere than today.

The ExoMars rover has to land somewhere with ancient rocks that are a record of that environment. That means landing somewhere older than 3.6 billion years, which is about the same age as some of the oldest rocks on Earth.

Mawrth Vallis

This area contains a large outflow channel known as Mawrth Vallis, which once discharged huge amounts of water onto the northern plains. The proposed ExoMars landing site is situated just south of this channel.

There are deposits of phyllosilicates that provide a unique opportunity to evaluate aqueous activity on early Mars and point to the possibility that habitable environments may have existed during the Noachian period (3.6 billion years ago).

This map shows a selection of NASA HIRISE camera images (stripes) overlaying a mosaic of ESA HRSC camera images. Zoom-in to reveal more detail and explore the surface at high resolution (1m/pixel).

Oxia Planum

The region is characterised by ancient highland cratered terrains that become increasingly eroded towards the highland-lowland boundary.

The region was chosen to include extensive, layered exposures rich in iron and magnesium phyllosilicates.

The phyllosilicate deposits in the area are seen as the key to the study of aqueous activity on early Mars and the search for evidence of habitable environments early in the planet’s history.

This map shows a selection of NASA HIRISE camera images (stripes) overlaying a mosaic of ESA HRSC camera images. Zoom-in to reveal more detail and explore the surface at high resolution (1m/pixel).

Hypanis Vallis

Hypanis Vallis is one of several valleys situated between two large outflow channels, Maja Vallis in the west and Shalbatana Vallis in the east.

Hypanis Vallis lies on an exhumed fluvial fan, thought to be the remnant of an ancient river delta at the end of a major valley network.

Distinct layers of fine-grained sedimentary rocks provide access to material deposited about 3.45 billion years ago.

This map shows a selection of NASA HIRISE camera images (stripes) overlaying a mosaic of ESA HRSC camera images. Zoom-in to reveal more detail and explore the surface at high resolution (1m/pixel).

Aram Dorsum

Aram Dorsum is located on plains of middle Noachian age, about 4 billion years old. It comprises layered sedimentary rocks crossed by a prominent inverted channel ridge, which is 80 km long and 1.2 km wide.

The ancient lakes and rivers at this site would have been favourable for the development of life, as well as for the preservation of its biosignatures. The long-lived aqueous conditions recorded in the migrating channel pattern would have been critical for establishing a habitable environment.

This map shows a selection of NASA HIRISE camera images (stripes) overlaying a mosaic of ESA HRSC camera images. Zoom-in to reveal more detail and explore the surface at high resolution (1m/pixel).

What's next?

Two ancient sites on Mars that hosted an abundance of water in the planet's early history have been recommended as the final candidates for the landing site of the 2020 ExoMars rover and surface science platform: Oxia Planum and Mawrth Vallis.

In the coming years, each of these sites will be studied in more detail than any other place on Mars. The year before launch, the European Space Agency will make the final decision.

Stay tuned!

Follow @opmteam on Twitter, and visit the ExoMars LSS page (formerly "Where on Mars?") to learn more about this visualisation project, and ESA's ExoMars 2020 mission.