Image: ESA/DLR/FU Berlin
Mars’ south pole, as seen from Mars Express

A lake of liquid water has been detected by radar beneath the southern polar ice cap of Mars, according to a new study by Italian researchers from the Italian Space Agency, published Wednesday in the journal Science.

The analysis derives from data collected by the venerable Mars Express orbiter, which has studied the red planet for nearly 15 years. This spacecraft carries an instrument called the Mars Advanced Radar for Subsurface and Ionosphere Sounding instrument (MARSIS). It was the first-ever radar sounder brought to another planet, but the team was unable to determine if it detected water on Mars until now.

Artistic impression of the Mars Express spacecraft probing the southern hemisphere of Mars.

The lake was found just 1-2 kilometers beneath the surface, near the south pole of Mars. This subglacial lake is about 20 kilometers (12.4 miles) wide and perhaps no more than a meter deep. Its discovery is the latest piece of evidence that suggests water was not only present on Mars in the past but is still flowing in some capacity today.

“In the case of Mars, and also in the case of Earth, liquid water is the material that certainly would produce the strongest reflections,”

– Roberto Orosei, a co-investigator of the MARSIS instrument at the University of Bologna in Italy and lead author of the new study.

USGS Astrogeology Science Center, Arizona State University, INAF.
Blue spots show signs of subsurface water.

The study says the subglacial lake on Mars is cold indeed, and rather salty. Water ice that is near the melting point is opaque to radio waves, and so the ice above the lake must be well below freezing. Accordingly, the subglacial water must be at least negative 10 degrees Celsius.

For this to be possible, the reservoir must be saturated with salts—likely salts of sodium, magnesium, and calcium, which have been discovered on the Martian surface. These salts can reduce the melting point of water to negative 74 degrees C, so the subglacial lake is likely between this temperature and around negative 10 or 20 degrees.

Since water is integral to life as we know it. A lake of liquid water, protected from deadly radiation by the planet’s thick crust, is a prime site to search for life. Because of its relative closeness to Earth, the lake may now overtake the icy oceans of Jupiter’s moon Europa as the best place to search for life.

Space agencies are now likely to scramble to send other craft there, possibly landers to drill down to sample the lake itself.


R. Orosei1, et al. Radar evidence of subglacial liquid water on Mars Science 25 Jul 2018: eaar7268 DOI: 10.1126/science.aar7268