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Scientists have discovered an underground lake of liquid water on Mars! While this isn’t itself evidence for life on Mars, it does raise some new possibilities.
Our SciShow Space episode about this: https://youtu.be/b8eNOOqi258

Hosted by: Hank Green

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Sources:
http://science.sciencemag.org/cgi/doi/10.1126/science.aar7268
http://science.sciencemag.org/cgi/doi/10.1126/science.aau1829
https://www.space.com/30673-water-flows-on-mars-discovery.html
https://www.space.com/21554-mars-toxic-perchlorate-chemicals.html

Images:
https://commons.wikimedia.org/wiki/File:Oblique_View_of_Warm_Season_Flows_in_Newton_Crater.jpg
https://commons.wikimedia.org/wiki/File:The_unfolding_of_MARSIS_boom_2_continues_ESA218825.jpg
https://www.nasa.gov/mission_pages/mars/images/marsis-caption-20080417.html
https://commons.wikimedia.org/wiki/File:South_Polar_Cap_of_Mars_during_Martian_South_summer_2000.jpg
If you listen carefully, you can hear the sound of space nerds everywhere jumping up and down and shrieking with excitement.

Because scientists just announced that they found a giant underground lake on Mars! This isn’t the first time we’ve found evidence for some type of liquid water on Mars.

But those were streaks of it, and they only show up seasonally, and we’re not even totally sure what they are. We’ve never found a permanent body of water on Mars, or anything close to this much of it in one place. And best of all, there’s a chance that if life exists, or ever existed on Mars, we might find evidence of it in this lake.

In the new paper, published today in the journal Science, a group of Italian researchers looked at data from MARSIS, an instrument on the European Space Agency’s Mars Express orbiter. MARSIS uses radar to look below the surface of Mars. It works kind of like the radar we use to detect planes here on Earth, by sending out radio waves and measuring how they bounce back, you can get an idea of what’s out there.

With MARSIS, scientists can also use the data to figure out some of the properties of the stuff the waves passed through and bounced off of. For this study, they looked at three years’ worth of observations of Mars’s south pole. It’s covered in a layer of mostly water ice, but about 1.5 kilometers below the surface, the waves reflected off of something weirdly bright and shiny, especially compared to the area around it.

Something big. Turns out, it was exactly what you’d expect to see if the waves were reflecting off of a boundary between ice and liquid water. The researchers looked into a few other possibilities, like that it was a layer of frozen carbon dioxide, but when they ran the numbers, liquid water was the only scenario that made sense.

They found that this water stretches across an area about 20 kilometers wide, and is either in a separate layer or mixed with some sediment in what’s possibly the most exciting sludge humanity has ever found. But no matter what form it takes, that is a ton of liquid water! Normally, it’s way too cold at Mars’s poles for water to stay liquid it’s thought to be around -68 degrees Celsius over there.

So for liquid water to exist, it must be full of salts that lower its melting point so much salt that it’s more like brine than water. Which brings us to the question on everyone’s minds:. What does this discovery mean for the possibility of life on Mars?

Well, first things first: even if life could survive in this underground lake, that doesn’t mean it’s there. This is not evidence for life on Mars. But it does raise some fascinating new possibilities.

Liquid water is essential for life as we know it, which is why practically all of our search for life on other worlds revolves around water. We’ve found evidence for lakes and rivers on Mars, but until now we thought they vanished billions of years ago. So finding a massive underground lake there today changes things.

A lot. The problem is, the water would be an extremely harsh environment it’s full of salts, and freezing cold. Some especially hardy microbes, known as extremophiles, can live in places no other life on Earth could survive, but these conditions are even worse.

So to learn more about whether life could survive in Mars’s underground lake, we turned to Nilton Rennó, an astrobiology expert at the University of Michigan. According to Rennó, the water is too cold for life as we know it to survive and probably also too salty. But that doesn’t mean there’s definitely no life there.

If there’s some source of heat below the surface that we don’t know about, it could mean the water is warmer and probably less salty than we think. Maybe to the point that life could survive. The other potential problem is the chemical composition of the salts dissolved in the lake.

We’re not talking table salt here this stuff is made up of perchlorates, chlorine-containing compounds that are toxic to humans. Martian soil is full of them. So if you ever get a chance to visit Mars’s underground lake, do not lick it!

But just because something is toxic to humans doesn’t mean it’s toxic to all life! In fact, there are microbes here on Earth that actually feed on perchlorates. Still, unless the water is much warmer and less salty than we think, it doesn’t look like life could stay alive in Mars’s underground lake.

Or at least … not right now. Mars used to be much warmer and wetter than it is today. And according to Rennó, ancient microbes could be preserved in the water for millions, if not billions of years.

Which means we now have a fantastic place to search for life on Mars. Of course, sending a mission to Mars to look for life a kilometer and a half below the surface is easier said than done. But maybe not impossible!

For more details on how we could look for evidence of life in this underground lake, plus more information about the research behind this discovery, we did a whole separate episode over on SciShow Space because we’re THAT excited about this! You can go to youtube.com/scishowspace to check it out. In the meantime, thanks for watching this special Breaking News episode of SciShow, and don’t forget to go to youtube.com/scishow and subscribe!