Several weeks ago, scientists revealed an astounding discovery of an underground lake on Mars. Not only is it a lake, but it is a lake containing water, based on the evidence collected. Numerous missions on and around Mars have focused on finding water, but this discovery might be the most promising yet.
The history of water and water evidence discoveries on Mars goes all the way back to 2003 and the Opportunity rover. The rover discovered microscopic mineral deposits inside of rocks, which suggested that water was present at some point on Mars (1). This discovery intrigued the science community and, in turn, more spacecrafts and rovers were dedicated to discovering water on Mars. One such mission was the Phoenix lander which, in 2009, found conclusive evidence of water near the North pole of Mars. The lander collected a soil sample for analysis, and through heating the sample, the lander was able to detect water vapor (2). More recently in 2015, the Mars Reconnaissance Orbiter (MRO) detected hydrated minerals on the surface of slopes on Mars. Although flowing liquid water was not discovered in this mission, the presence of minerals suggests that water had flowed recently (3).
The latest discovery of water on Mars came from the Mars Express spacecraft, made by the European Space Agency. This spacecraft has been orbiting Mars since 2003 and analyzes various aspects of the Martian surface and subsurface. One important tool on board the Mars Express is the Mars Advanced Radar for Subsurface and Ionosphere Sounding (MARSIS). Basically, this tool sends out radar signals down to the surface of Mars to figure out what the surface looks like and what could be hiding just below. In 2008, MARSIS detected bright reflections coming from an area near the Martian south pole. According to scientists on the Mars Express team, this could mean the area houses briny water beneath the surface. Mars Express continued to gather data from this region for the next few years, but most of the data collected did not help clarify this highly reflective underground region. The team took another three years to collect even more data that would help determine the possibility of water, and their patience was worth it. Through comparisons of similar data gathered from Earth, the data collected by Mars Express allowed scientists to conclude that this region of Mars holds a subglacial lake only a few feet deep but about 12 miles across. Although this is good news for future manned Mars missions, there is a big downside. The lake is several kilometers underground, so it would require astronauts to drill a far way down. Even then, the lake could end up being some moist sediments, but future missions with new tools will surely analyze this lake as much as possible (4,5).