Researchers have long debated over whether Mars contains liquid water, a question that has finally (for the most part) been settled.
Mars is now cold, barren and dry but used to be warm and wet. In 1987, the astronomer Stephen M. Clifford theorized that liquid water might be hiding, deep below the planet's polar ice caps. "This thrilling discovery is a highlight for planetary science and will contribute to our understanding of the evolution of Mars, the history of water on our neighbor planet and its habitability", he said. A NASA spacecraft with the same mission and similar technology hasn't detected the body of water, suggesting that it may be transient and not the permanent source that life would need to survive.
The readings turned up evidence of a particularly bright radar reflection in a 12-mile-wide (20-kilometer-wide) area.
"If there is microbial life operating there, it's operating under conditions that would be at the very limits of what we know life operates under here on Earth", said Brent Christner, a microbiologist at the University of Florida. So far, more than 400 such lakes have been found beneath the surface of the frozen continent.
For the water to remain liquid under the cold ice at low temperature and pressure, it must be a brine saturated with perchlorate salts that lower the freezing point of water. Some, like Mars Express, are orbiters, whereas others (such as the incredible Spirit and Opportunity) are rovers.
Satellites and telescopes have shown us ice deposits at the planet's polar regions. For this water to be in liquid form at subzero temperatures means that the water probably has very high salt content.
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It has always been suspected that the Red Planet is not as dry and arid as it looks. Its radio pulses traveled through the Martian surface and polar ice caps, then reflected back to the spacecraft's antenna.
The scientists who analyzed these radar echoes were careful to consider all the things that could have made the echoes they measured, including explanations that don't involve liquid water, and they were able to rule out most of those explanations.
Using the Mars Advanced Radar for Subsurface and Ionosphere Sounding (MARSIS), a team of Italian researchers discovered liquid water on Mars.
Researchers said they are not sure how far down it goes, but may be around one meter (three feet) deep.
Another ground-penetrating radar is aboard NASA's Mars Reconnaissance Orbiter, called SHARAD, which is short for "shallow radar". NASA's website says SHARAD is created to see up to 4 km (2.5 miles) under the surface, which would include the zone where Mars Express detected signs of water.
Italian astrophysicist Roberto Orosei speaks during a press conference at the Italian Space Agency headquarters in Rome, Wednesday, July 25, 2018.
"It's unusual that SHARAD can not confirm this discovery. In fact, SHARAD cannot penetrate through the ice here and no one understands why it can't", Stillman said. "This suggests that something unusual is happening here. Thus, I'm skeptical about this discovery".
According to Michael Meyer, lead scientist for NASA's Mars Exploration Program at the agency's headquarters in Washington, it took multiple spacecraft over several years to solve the this mystery which has now led to discovery of liquid water on the surface of the red Planet. Just like Earth, Mars has salts (much more than in Earth's oceans) in its water.