Only half of all landings have been successful

A landing on Mars is difficult. The atmosphere is so thick that the craft needs a sturdy heat shield not to burst into flames, but on the other hand, it is so thin that a safe landing requires more than a parachute.

are only talking about a small prototype. A manned mission would require an oxygen machine that is 100 times larger than MOXIE, which is the size of an ordinary car battery. Mars includes plenty of ice based on water. Both poles are covered in thick ice caps. Mars has seasons just like Earth, and in the winter, the poles are covered in several metres of frozen carbon dioxide, but particularly by the north pole, there is free access to water ice for all six months of the summer half. A little further towards the equator, there is ice based on water right beneath the surface, as revealed by the Phoenix lander in 2008. It landed at 68 degrees north latitude – comparable to northern Scandinavia on Earth – and the lander’s robotic arm did not have to remove very much of the Martian dust, before the ice appeared.

In January 2018, images from the Mars Reconnaissance Orbiter satellite showed that there is also thick ice closer to the equator. At degrees of latitude corresponding to Denmark on Earth and similarly in the southern hemisphere, scientists spotted a layer of ice, when they scrutinized images of steep slopes. In some places, the ice cover is more than 100 m thick.

Radars scan the underground

NASA scientists believe that there is water in the shape of ice under the dust of one third of Mars, and in many places, the ice is hiding at depths of only 1-2 m. The water cannot only be used for drinking purposes, it is also easy to split into oxygen and hydrogen, which can be used as rocket fuel. You could imagine a future, in which astronauts on Mars would extract the fuel which is to bring them back to Earth.

The three Mars rovers that are to explore the planet from 2021 all bring ground radar equipment, which can provide details about the underground layers down to a depth of 10 m and show, whether a thick layer of ice is hiding beneath the dust. The ice is not only interesting in connection with future settlement, rather also because it provides us with knowledge about Mars’ geological history and can show where the water went.

Satellite images show clear lines in the landscape, and most scientists think that they mark the water level – i.e. prehistoric coast lines. Based on this data, scientists from the University of California, Berkeley, USA in March 2018 concluded that Mars included a large ocean by the name of Arabia four billion years ago. The ocean contained 41+ million km3 of water and was 10 times larger than the Mediterranean.

The water did not stick to oceans, it also flowed in large rivers that cut canyons in the landscape. In several places – such as the Gale crater – lakes also formed. Curiosity is roaming the ancient lake bed to find one piece of evidence after the other that the crater included a large freshwater lake, which involved favourable conditions of life.

Today, the liquid water has disappeared from the Martian surface. Partly, temperatures are too low, partly the water would quickly evaporate due to the low atmospheric pressure. But some 4.6 billion years ago, when Mars was very young, temperatures were higher and the atmosphere denser. By then, the planet even also had a magnetic field which helped hold on to the atmosphere. When it disappeared, cosmic radiation could hit the air molecules, sending them into space.

The last liquid water on the surface probably disappeared about three billion years ago, but near the equator, liquid water could still exist beneath the red dust, when the "heat" of summer causes temperatures to rise above zero degrees, and some microorganisms could have survived.

Samples scrutinised on site

If Mars includes life today, it is probably to be found beneath the surface. Mars is subjected to intense cosmic radiation, which would quickly kill off any organisms on the surface. Similarly, any fossil remains of microorganisms would also long since have disintegrated in the hostile environment. So, the European ExoMars rover brings a drill that can work its way two m into the underground, where the chances of finding evidence of life are greater, to extract drill samples.