Digging for Alien Life: Where to Land the ExoMars Rover

The ExoMars Mission

In 2020 the European Space Agency (ESA) will send its ExoMars rover into space, heading for our neighbouring planet Mars. It will search for signs of life on Mars, equipped with a two metre drill to dig deeper into the Martian surface than ever before.

The question today is, where will it land? Mission scientists and engineers have been debating the question of landing sites since 2013, trying to balance safety for the rover against places of scientific interest, and today they are down to the final two choices: Oxia Planum and Mawrth Vallis. And this key choice on where to land is about to be made closer to home than you might think!

These final two sites were picked by a group of specialist scientists called the Landing Site Selection Working Group, who have expertise in all aspects of Mars from its geology to its weather. Several members of the group are from UK universities, including local Mars expert Professor John Bridges from the Space Research Centre at the University of Leicester. He and the rest of the group will be making the final decision from Leicester in November 2018.

Ahead of this key choice, let’s take a closer look at these two sites and the main requirements for a landing a rover on Mars.

How to land on Mars

When you send something to land on a foreign planet or moon, the first and most important criteria is that the landing site provides the best chance of a successful landing. A lot of time, effort, and money goes into designing and building the equipment for the mission.

The ExoMars mission, as a basic concept, was first proposed in 2001. However, Mars is a notoriously difficult place to land, due to its thin atmosphere. If parachutes are used, the spacecraft needs as much time as possible to slow down, and so landing sites with low elevations are preferred. As well as a low elevation, you also need the terrain to be smooth and flat. Large rocks and boulders can damage the rover and any steep slopes may cause it to fall over.

Beyond this, there is the question of how to power the rover. If the rover is using solar panels the landing site needs to be in a location where it will get plenty of sunlight – i.e. the equator. Regions around the equator also have relatively moderate temperatures in comparison to the harsh temperatures in other areas. This provides the rover with the best chance of not freezing over and shutting down.

Finally, the landing site must be suitable for the science of the mission. If your rover is built to examine the polar regions of your planet, for example, obviously you would want to land near the poles! ExoMars is being sent to find signs of life and so it needs to land in the most likely area for life – past or present.

Oxia Planum

The first landing option is Oxia Planum, a plain situated north of the Martian equator. This region features one of the largest exposed regions of clay rocks, aged around 3.9 billion years old.

Oxia Planum is a nice, flat plain in a low-lying area, and it is also near the equator, so it achieves all of requirements for landing a rover on Mars. But the main reason why this site has been picked is for its scientific mysteries. Its clay rocks are rich in iron-magnesium compounds, which is a typical indication that water was present. If this is true, then there’s the possibility that life once existed in this region – and perhaps still holds fossilised evidence!

Mawrth Vallis

The second option is Mawrth Vallis, a valley on Mars believed to be formed by massive flooding during Mars’ ancient past. Like Oxia Planum, this area is rich with clay minerals and again provides some of the best opportunities to search for life.

Mawrth Vallis also offers a chance to get a greater understanding of the geological history of Mars. In this region, there are many different exposed layers, including a layer of volcanic material, which would allow the rover to sample the minerals throughout Martian history. But there’s extra risk– Mawrth Vallis has a higher altitude with steeper slopes and so is a more dangerous choice for the landing.