A large reservoir of liquid, salty water was discovered underneath the polar cap of Mars, researchers with the Italian Space Agency (ASI) announced on Wednesday.
The lake was detected beneath some 1.5 kilometers of ice near Mars' south pole through a radar instrument working from a European spacecraft orbiting around the planet, according to ASI chief scientist Enrico Flamini.
"It took us many years of analysis and struggles on data to find the right method in order to be sure that what we were observing was definitely liquid water," Flamini told a press conference.
"Such work has involved many researchers coming from different Italian institutes, young people who had the energy and ability needed to work intensively on data," he added.
The scientist explained evidences of the past presence of water on Mars were already collected some 40 years ago -- since NASA's Viking mission was launched in 1976 -- for example observing traces of the dry beds of superficial lakes and rivers.
Yet, the new research would provide the first proof of a large and stable reservoir of liquid water ever found on the red planet.
The lake measured approximately 20 square kilometers, and was made of water "surely much below the zero Celsius," ASI said in a statement.
Such findings were based on data collected by radar sounder MARSIS (Mars Advanced Radar for Subsurface and Ionosphere Sounding), which was designed by Italian researchers with a contribution from NASA's Jet Propulsion Laboratory and the University of Iowa in the United States.
The instrument was positioned on board of the European Space Agency's Mars Express spacecraft in 2003, and started scanning Mars' surface in July 2005.
The discovery of the lake, more specifically, was based on information collected by the instrument between May 2012 and December 2015.
MARSIS used low-frequency electromagnetic waves, transmitting its pulses toward the red planet, researchers explained. Such waves were able to penetrate the surface up to 4-5 kilometers, and reacted differently according to the various types of material they met.
Then, they were reflected back to the radar aboard the Mars Express, providing geological information on the portion of planet under examination.
The radar was capable of analysing "the geophysical characteristics of Mars' deep layers, and also accurately measure the state and variations of the Martian ionosphere," according to ASI.
"MARSIS is an instrument of innovative conception, and it is completely different from any other radar ever tested in a space mission," Flamini further explained.
Researchers also provided one hypothesis to explain why water underneath would remain liquid despite being several degrees below zero Celsius: the presence of a considerable quantity of salts.
"The salts -- which are likely similar to those found by NASA's Phoenix spacecraft in the ice of the northern polar area (of Mars) -- work like 'antifreeze', helping maintain the water in a liquid state," ASI said in the statement.
"Researchers believe there may be other areas with conditions favorable to the presence of deep water on Mars and now, having developed the right method of analysis, they will be able to continue to investigate," it added.
The team carrying out the research comprised 32 experts from the Italian Space Agency, the National Institute of Astrophysics, National Research Council, and three Italian universities.
