Water is available on the Red Planet in quite considerable quantities: For example, at both poles you will find an ice sheet several kilometers thick, which consists mainly of water. Indications of water in a liquid state, however, have repeatedly turned out to be the wrong track. So it threatens now also a "Science" study from the year 2018 to go. The supposed lake at the South Pole of Mars, which experts wanted to have recognized in radar data at the time, could just as well be an area of volcanic rock or the loamy deposits of an ancient riverbed, says a research group. The critical reanalysis of the radar data comes from a team led by Cyril Grima from the University of Texas at Austin. It is published in »Geophysical Research Letters«.
According to the original study, the lake with the liquid water should be located at a depth of about one and a half kilometers not far from the actual polar cap, more precisely in the ice-rich layer deposits located there. These deposits were measured by the Mars Advanced Radar for Subsurface and Ionospheric Sounding (MARSIS) on board ESA's Mars Express probe. In their data, Roberto Orisei and his colleagues from the Istituto Nazionale di Astrofisica in Bologna came across a surprisingly strong signal, which they interpreted as reflections on an underground lake.
Cyril Grima's team now looked at the cycling measurements of other regions of Mars, which are not covered by ice, and simulated how the signal would change from these regions if it had run through one and a half kilometers of ice. It was shown that smooth rock layers of volcanic origin under simulated ice cream look as much as the supposed lake under the real ice. Such levels with a volcanic stone are available on Mars. For other researchers, the signal from the Marssüdpol more fits sediments, such as they arise in river beds. That would be an indication of the early days of Mars when there was probably still liquid water there.
Other experts had already raised doubts about the existence of such lakes under the ice. "For water to remain liquid so close to the surface, there must be both a very salty environment and a local heat source. But that doesn't fit with what we know about this region," says Grima. In this respect, it is more plausible to assume that the more banal explanation for the conspicuous radar echo at the South Pole of Mars is also the correct one.
