The discovery could have significance both for the study of the Red Planet's history and for its future exploration.
The Russian FREND neutron telescope aboard the artificial Mars satellite Trace Gas Orbiter has found a number of ice 'deposits' on the fourth planet that were previously undetectable. Especially strange is the fact that this time it has been able to identify large amounts of water ice in the warm regions of the planet, where, in theory, water ice is more difficult to keep. How exactly it got there is not yet clear. The paper is published in the Journal of Geophysical Research: Planets.
FREND stands for Fine Resolution Epithermal Neutron Detector, and was built at the Space Research Institute of the Russian Academy of Sciences. The device detects neutrons emanating from the surface of Mars. Their energy can distinguish neutrons "bounced" from hydrogen atoms in the top meter of the Martian soil, and thus understand whether there is water there. Similar Russian-made instruments are already working on the surface of the Red Planet (on Curiosity). However, FREND differs from them by a much larger field of view. It is carried by the European satellite Trace Gas Orbiter with an orbit of 400 kilometres, allowing the study of the entire Martian surface.
The FREND detectors are shielded by neutron absorbing materials. This allows it to "see" neutrons precisely at right angles downwards from it, which greatly increases the resolution of the instrument as a whole. It has thus produced the most detailed map of hydrogen in the upper Martian soil layer. The more orbits around the Red Planet, the higher the resolution of the maps obtained. Although the instrument is now a long way off, it has already produced an unprecedentedly accurate map of this kind.
As noted by scientists at the Space Research Institute, such maps contain a number of surprises. Beyond 60 degrees latitude, there is plenty of water ice in the ground in the northern and southern hemispheres - in fact, there is something like terrestrial permafrost, and this was not a surprise. But also at lower latitudes, up to 50 degrees latitude, FREND was able to find 23 areas where the hydrogen content suggested the presence of 5% or more water in the ground.
Particularly interesting are points 10 (on the map), near Arabia, and 17, in the centre of Arabia. According to the new data, 23-24% of the water in the ground is there. Such a high concentration clearly indicates the presence of pure water ice (not even permafrost in the usual sense of the word) in the upper metres. It appears to be covered by only a thin layer of sand, even though both points lie at very low latitudes. It remains unclear why the ice there has not been sublimated into water vapour during all this time.
In addition, more than 20% water by mass has been found by FREND in Mariner Valley Canyon (point 1 on the map). And this region makes up a large part of the entire canyon. At three points, the water content is particularly high - it looks like clear ice is deposited there.
The Mariner Valleys are regarded as one of the most promising places to set up a research base. They are up to 11 km deep (the deepest canyons in the solar system), so the atmospheric pressure at their bottoms is higher than on the planet as a whole. From time to time, thin clouds of water vapour and even morning fog form over the valleys.
The presence of water is critical to the establishment of any research base on Mars. High latitudes (above 60 degrees), however, are not very suitable for it. Average temperatures there are much lower, there is very little use of solar panels in winter and the search for Martian bacterial life has little prospect. Low latitudes are in all these senses more favourable.