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Back in 2018, scientists found what seemed to be a massive lake deep under the ice near. Mars's south pole.

And that was pretty surprising, because even though there's plenty of evidence that water used to flow across the surface, the chances of there still being liquid water seemed pretty slim. For one, the pressure from Mars's atmosphere is so light that it would be impossible for water to stay in a liquid state in most places. And then there's the fact that its surface temperature averages about -63 degrees Celsius.

But an underground lake wasn't out of the question. And last week, a study published in Nature Astronomy provided new evidence that this massive lake exists—and that there are smaller pools around it. The study was based on data from the spacecraft Mars Express, which also made the 2018 discovery.

It's currently orbiting the Red Planet and bouncing radar off it to explore beneath the surface. [NASA/JPL-Caltech] How can a satellite measure what's under the ground? Well, I'll tell you... Mars Express does this by sending down pulses of radio waves, which penetrate the crust and bounce back in different ways depending on the material they travel through.

So the echo of these waves can help us tell the difference between water and rock, even if we can't see them. In the latest study, scientists collected a bunch of this radar data and analyzed it using a technique we use on Earth to look for liquid water below glaciers, in places like Greenland and Antarctica. It's an approach that's designed to distinguish pools of water from frozen or dry layers of the crust.

And sure enough, they found an underground lake right where they expected, about 20 by 30 kilometers wide. But it wasn't alone! They also found evidence of other, smaller bodies of water surrounding this lake.

The researchers still aren't sure why exactly these lakes exist. They may have formed after some underground volcanic activity warmed up the area about a million years ago. And then, as the temperature dropped, natural salts dissolved in the water may have kept it from freezing, just like road salt keeps water from becoming ice.

Thanks to all that salt, this water isn't likely to sustain future human explorers, but it gives us a new place to look for current or past life. In other space news, astronomers have gotten one step closer to solving a mystery about the Sun that's been eluding us for decades. Since the 1940s, scientists have known that the Sun's corona, or atmosphere, is around a million degrees Celsius.

But its surface is only around 6000 degrees. [Luc Viatour] And that's pretty confusing. Because normally the farther away you are from a hot thing, the less hot it is. That's how thermodynamics works.

So some process has to be heating the corona, and scientists aren't sure what it is. But last week, in another paper published in Nature Astronomy, scientists revealed that they may have found an important clue. They were using data collected by three separate solar observatories, including NASA's IRIS spacecraft, which has a high-resolution camera tracking the movement of matter and energy through the Sun's lower atmosphere.

Back in 2014, that camera was able to capture the first clear look at thin, bright explosions of light known as nanojets. Scientists believe these form from nanoflares, which are arcs of plasma and magnetic field lines—like miniature solar flares. They form when the Sun's tangled magnetic field lines break and reconnect thanks to the movement of charged particles.

Normally, nanojets are hard to spot against the bright Sun, but in 2014 there was what's called a coronal rain event. That's when a bunch of cool plasma flows from the corona down to the surface of the. Sun in what kind of looks like a waterfall.

Except like, made of plasma. And toward the end of this event, scientists spotted a bunch of nanojets streaking across their images, perpendicular to the arcs formed by the coronal rain. It was the first clear observation of this phenomenon, which was exciting.

But to be sure they were actually looking at what they thought they were, scientists ran simulations to see if nanojets like the ones they observed would form under the existing conditions on the Sun. And the simulations checked out! Together, these findings help back up a hypothesis scientists have had for years about the heating of the corona.

The formation of one nanoflare can trigger another, and so on. So an avalanche of nanoflares might generate enough energy to heat the atmosphere to the temperatures we measure. Scientists will still need to keep an eye on the Sun to figure out how frequent these nanoflares actually are and whether or not their energy is doing any significant heating.

But luckily, two solar spacecraft are on the way. In the next few years, NASA's Parker Solar Probe and the ESA's Solar Orbiter will give us an unprecedented view of the Sun—and hopefully help us solve this mystery for once and for all. Thanks for watching this episode of SciShow Space News, which is produced by Complexly.

If you want to keep imagining the world complexly with us, check out Bizarre Beasts! Each month, we'll introduce you to a new bizarre beast and explore what makes these animals so weird to us—from birds whose babies have claws on their wings to lizards with glowing bones. And if you want to take a bizarre beast home, check out the Bizarre Beasts pin club!

You can find a link for that and the channel in the description below. {♫Outro♫}.