Scientists certainly have taken a look at the underground lake found on Mars in 2018. It seems that this lake might not be the only one.
To add to that, new clues might help us understand why the Sun’s atmosphere is so much hotter than the surface.
From what we know today, it seems that almost all water on Mars today exists as ice. However, it also exists in small quantities as vapor in the atmosphere.
What was thought to be low-volume liquid brines in shallow Martian soil, also called recurrent slope lineae, may be grains of flowing sand and dust slipping downhill to make dark streaks. The only place where water ice is visible at the surface is at the north polar ice cap. Abundant water ice is also present beneath the permanent carbon dioxide ice cap at the Martian south pole and in the shallow subsurface at more temperate conditions. More than 5 million km3 of ice have been detected at or near the surface of Mars, enough to cover the whole planet to a depth of 35 meters (115 ft). Even greater amounts of ice are likely to be locked away in the deep subsurface of this fantastic red planet.
Some amounts of liquid water may occur transiently on the Martian surface today, but limited to traces of dissolved moisture from the atmosphere and thin films, which are challenging environments for known possible life.
No large standing bodies of liquid water exist on the planet's surface, because the atmospheric pressure there averages just 600 pascals (0.087 psi), a figure slightly below the vapor pressure of water at its melting point.
It seems that under average Martian conditions, pure water on the Martian surface would freeze or, if heated to above the melting point, would sublime to vapor.
Experts believe that before about 3.8 billion years ago, Mars may have had a denser atmosphere and higher surface temperatures, allowing vast amounts of liquid water on the surface, possibly including a large ocean that may have covered one-third of the mysterious red planet.
It seems that water has also apparently flowed across the surface for short periods at various intervals more recently in Mars' history. Aeolis Palus in Gale Crater, explored by the Curiosity rover, is the geological remains of an ancient freshwater lake that could have been a hospitable environment for various microbial life.
To date, no proof has been found of past or present life on Mars. Cumulative evidence shows that during the ancient Noachian time period, the surface environment of Mars had liquid water and "may have been" habitable for microorganisms.
Underground lakes on Mars are sure exciting. 3 new underground lakes have been detected near the south pole of Mars. Scientists also confirmed the existence of a 4th lake. However, the lakes are also thought to be extremely salty (this could pose challenges to the survival of any microbial life forms).