An article published in the journal “Nature Communications” offers new confirmation of the presence of very salty liquid water on Mars underground. A team of researchers led by Roberto Orosei of the Italian National Institute of Astrophysics and Elena Pettinelli of the Italian Roma Tre University examined detections conducted with ESA’s Mars Express space probe’s MARSIS instrument together with laboratory experiments and simulations to rule out that the data collected were generated by materials other than salty liquid water.
The possibility that there’s liquid water on Mars under certain particular conditions underground and with a high rate of salinity was first proposed in a study published in July 2018. It was based on findings to which other researchers tried to offer alternative explanations. This is a normal practice in the world of science, especially for detections conducted from the orbit of materials present in the Martian subsoil which in this case led to different conclusions regarding the nature of the data collected.
The MARSIS (Mars Advanced Radar for Subsurface and Ionosphere Sounding) instrument is a radar that detects signals from the Martian subsoil that are influenced by the nature of the materials they passed through. However, it can be difficult to have certainties when different materials can provide very similar detections.
In such a case, the question is made even more complex because the temperatures of the materials also influence the effects on radar detections but replicating the Martian conditions to conduct laboratory tests isn’t easy. For this reason, in the years following the first study, others came out that offered conflicting conclusions.
The study just published in the journal “Nature Communications” offers confirmation of the presence of salty liquid water in the so-called South Polar Layered Deposits (SPLD). Roberto Orosei and Elena Pettinelli’s team conducted laboratory experiments and simulations to study the physical properties of these deposits and try to establish if other materials besides salt water can generate the signals detected by the MARSIS radar. Their conclusion is that there are no others.
The study focused in particular on the deposit called Ultimi Scopuli, in the area of Mars’s southern polar cap. The image (Courtesy Sebastian Lauro et al. All rights reserved) shows a topographic map of that area obtained using NASA’s Mars Global Surveyor (MGS) space probe’s MOLA (Mars Orbiter Laser Altimeter) instrument in which the dotted lines indicate the measurements made with the Mars Express space probe’s MARSIS instrument.
The researchers calculated that the dust content in the polar deposits is between 5 and 12% and the temperature at the base of the ice can’t exceed the value of 230 Kelvin, or -43° Celsius. Planetary geologist Graziella Caprarelli of the University of Southern Queensland, among the authors of this study, explained that this study also shows that the temperature at the base of the deposit calculated so far was underestimated and can easily reach 200 Kelvin, or -73° Celsius.
According to Roberto Orosei, who is also the MARSIS instrument’s principal investigator, these results show that the detected signals can’t be explained by an interference existing in the boundaries between multiple layers without the presence of water. This is the alternative suggested in an article published in the journal “Nature Astronomy”. In short, confirmations arrived of the existence of underground lakes of salty liquid water but it’s by no means certain that the case is closed.
