An article published in the journal “Science” describes the discovery of an underground lake of liquid water on Mars. A team of researchers led by Roberto Orosei of the National Institute of Astrophysics and composed of researchers belonging to Italian research centers and universities used data collected by ESA’s Mars Express space probe’s MARSIS radar to collect evidence that at the south pole at about 1.5 kilometers of depth there’s water that is liquid.
Years of surveys showed that water was in liquid form on Mars when the planet was young and in many ways similar to the Earth, but today the conditions are very different. Possible flows of liquid water on its surface were discovered but those are isolated and limited cases. Water ice exists in the polar regions and is buried in various soil layers, but someone hypothesized that in the depths of the subsoil water could be liquid.
ESA’s Mars Express space probe is equipped with MARSIS (Mars Advanced Radar for Subsurface and Ionosphere Sounding), which is called a radar sounder, which is a radar that operates at frequencies between 1.5 and 5 Mhz that among other things can carry out surveys at great depth, up to 5 kilometers if the characteristics of the soil allow it. It was proposed by the Italian Space Agency, which subsequently managed its construction, precisely to investigate Mars’ subsoil.
Surveys in the southern polar area of Mars were carried out with MARSIS during the Mars Express mission, but in particular the ones carried out between May 2012 and December 2015 were examined. They attracted the interest of scientists because they show an area of about 20 square kilometers where the subsoil is very reflective and is surrounded by other areas that are not.
The image (Context map: NASA / Viking; THEMIS background: NASA / JPL-Caltech / Arizona State University; MARSIS data: ESA / NASA / JPL / ASI / Univ. Rome; R. Orosei et al 2018) shows the South Pole region on Mars, an inset showing the area where the lake was found with the radar footprint that identified the water and in the right panel the subsoil’s radar profile in that area.
The analysis of the data gathered by MARSIS was long and complex but the results indicate that in the area that shows peculiar characteristics there’s an underground lake where water is in a liquid state. The key factor was the electric permittivity of the highly reflective area that corresponds to the presence of materials that contain a large amount of liquid water.
Elena Pettinelli, co-author of the research, compared this Martian lake to some lakes that exist under the Antarctic ice. However, the temperature in the Martian lake is much lower and this means that its water must be extremely salty in order to remain liquid.
In essence, the discovery is interesting but might change nothing about the search for life on Mars and possible manned missions. The conditions in that lake are far more extreme than those of any Earth’s lake for temperature and salinity so life forms should have extreme adaptations to survive. That’s not impossible but it’s certainly unlikely. The lake’s depth adds to the difficulty in reaching the water for any astronauts or even for a robot programmed to try to analyze its contents.