It took years of patient analysis, but today a team of Italian scientists announced that an Italian-U.S. radar instrument, MARSIS—which has been observing Mars since 2005—finally found what it was looking for: a lake of liquid water a mile below the Martian surface near the planet’s south pole. The researchers report their finding in this week’s Science magazine.
The existence of subsurface water was proposed more than 30 years ago, so the discovery comes as no surprise. But the MARSIS team had to use a new method of getting high-resolution raw data from their instrument, then had to combine three and a half years’ worth of observations—29 separate radar profiles—before they were confident in their conclusion.
Judging from how radar signals beamed down to Mars bounced back to the spacecraft, the scientists believe they’re seeing a 20-kilometer wide shallow body of water, capped by 1.5 kilometers of hard ice. The character of the signals even helped the researchers distinguish between water and carbon dioxide ice, an alternate explanation for the radar signals seen by MARSIS over the last 13 years.
Before you start imagining Martian scuba dives, this "lake" is estimated to be only a few feet deep. And the MARSIS team can’t completely rule out "water-saturated materials" rather than plain old liquid water. If it is a lake, it’s probably several times saltier than Earth’s oceans—more of a brine.
Still, it’s a breakthrough, the first substantial body of water found on Mars, not millions of years ago, but today. And, say the authors, "there is no reason to conclude that the presence of subsurface water on Mars is limited to a single location."
That’s encouraging, because this lake, if it is that, will be very hard to reach. Drilling on Mars will be extremely difficult, and space engineers are still at a very early stage of developing the necessary technology. The drills on U.S. and European landers planned for launch to Mars in 2020 will only go down a few feet. And although lakes even deeper than the newly discovered Martian lake have been drilled in Antarctica, working on Earth is way, way easier than working on another planet.
So it may be that other suspected wet spots on Mars, such as the "recurring slope lineae" seen in numerous locations near the surface, may be far easier to reach. But it’s good to know this new lake is there.