Several years into the mission, MARSIS scientists began to see small, bright echoes under the south polar ice cap-so bright that the reflection could indicate not just rock underlying the ice, but liquid water.
Though the temperature on Mars may be too cold for pure water, Orosei and fellow researchers from a number of Italian instituitions noted it was possible that the water was mixed with dissolved salts of magnesium, calcium, and sodium to form a brine, researchers said.
"We interpret this feature as a stable body of liquid water on Mars", the study said.
Lakes might even turn up at lower, warmer latitudes-a location more suitable for a martian microbe, says Valèrie Ciarletti of the University of Paris-Saclay, who is developing a radar instrument for Europe's ExoMars rover, due to launch in 2020.
"I've been studying life in ice for 35 years", he said.
If confirmed, this would be the most significant body of liquid water found on Mars to date.
But there has been no conclusive evidence of liquid water existing on the planet in its current state until now.
Care to take a dip on Mars? With this, radar pulses were sent outward, ultimately bouncing back to the spacecraft.
These reflections "provide scientists with information about what lies beneath the surface". They were not the first successful landing-that credit belongs to the Soviet Union's Mars 3 lander-but they were the first landers to complete their task, which was to directly sample the surrounding soil, rocks and air while looking for signs of life. Further investigation revealed a roughly 12 mile wide area located around one mile below the planet's icy surface which produced a radio profile similar to that of one of Earth's subglacial lakes.
But it is quite likely that this body of water isn't a big lake. Calculations have suggested that these conditions may be met at the Martian poles, where large ice caps composed of both water and frozen carbon dioxide exist.
Even if this new discovery is validated, experts are lukewarm about whether this body of water would be suitable for life.
Scientists have also traveled deep underground into mines and found microorganisms related to ancient species that once lived in watery environments much closer to the surface. That will allow scientists to create models of the heat flowing out of the planet, like a cake that's cooling off after it has been baked - and should give insight into whether it's plausible that the temperature could be high enough to keep water in liquid form at that depth.
The region corresponded to a basin, adding to speculation that liquid water had flowed into this spot. New radar collections starting in 2012 showed a much stronger signal, Pettinelli said.
Authors of the Science paper, "Radar Evidence of Subglacial Liquid Water on Mars", include Orosei, Flamini and Cicchetti, plus S.E. Lauro, E. Pettinelli, M. Coradini, B. Cosciotti, F. Di Paolo, E. Mattei, M. Pajola, F. Soldovieri, M. Cartacci, F. Cassenti, A. Frigeri, S. Giuppi, R. Martufi, A. Masdea, G. Mitri, C. Nenna, R. Noschese, M. Restano and R. Seu. There, as on Mars, the surface is barren, but is more hospitable farther down.