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Go to CuriosityStream.com/Space to learn more. [♪ INTRO]. Today, Mars looks dry, dusty, and barren.

But over the years, scientists have found all kinds of evidence that the planet was once full of water. They've found empty riverbeds, sediment deposits, and signs of water erosion, and now, they're trying to figure out if this barren rock could have once had the right ingredients to host life. The more they search, the more they discover that life totally could have been possible, and now, there's even more to think about.

Because last week, scientists announced the first geological evidence that Mars used to have a global system of underground, interconnected lakes. Besides just being very cool from a geology standpoint, that also suggests that some low-lying regions of the planet could have been in contact with water for a long time. And if life ever existed on Mars, that might have been a prime spot.

If underground lakes on Mars sound familiar, it might be because of news from this summer:. Last July, scientists announced that they had found evidence for a salty, underground lake on Mars today, hiding under the planet's south pole. But this discovery isn't directly related to that.

This time, scientists were looking at Mars's past. And they did it by studying 24 deep craters in Mars's northern hemisphere, using data from the European Space Agency's Mars Express mission. Inside them, they found channels carved into the crater walls, along with valleys where groundwater likely seeped to the surface.

They also found deltas where water levels went up and down, and places where flowing water deposited sediments. In other words, they found features that could only have formed from water pooling and flowing and changing over time. The researchers suggest that this water may have come from a network of underground lakes, which likely formed as the climate changed.

As solar wind and radiation stripped a young Mars of most of its atmosphere, the planet grew frigid, and water that once flowed over the surface settled underground. This planet-wide groundwater system may have even been linked to Mars's ancient ocean, too, since the water level in these basins closely lined up with some of the old shorelines. If the team is right, if this deep water table did cover the planet, the paper's authors think it's also possible that life could have existed underground.

And if so, they're hopeful that there could still be signs of it in the sediment of these deep basins. It's not a totally ridiculous idea, either. As part of the study, researchers looked at images of the craters taken by tools onboard.

NASA's Mars Reconnaissance Orbiter. Based on how the craters reflected light, the researchers were able to identify the compounds inside of them. And they found that five of the craters had minerals like clays and carbonates that scientists believe are related to the beginnings of life on Earth.

So maybe there's something more down there, too. Of course, these findings are preliminary right now, and they can't prove that a groundwater network even existed, let alone had a bunch of things swimming around in it. But as we keep developing missions to Mars, we officially have one more thing to investigate.

Someday soon, we might even be able to send astronauts to sample these craters ourselves. Because over the weekend, SpaceX, one of the major contenders racing to get humans to Mars, reached a major milestone. This weekend, the company successfully demoed their commercially-built spacecraft, the Crew Dragon, which could be used to transport humans to the International Space Station as early as this summer.

The mission was called Demo-1, and its goal was to prove that the crew capsule could launch, dock at the Space Station, and safely return to Earth. It was also done to test certain steps that can't be perfectly modeled on the ground, like the capsule's automated docking system and re-entry system. The Dragon was launched early Saturday morning and was packed full of supplies and had a robotic passenger named Ripley.

Yes, after Ellen Ripley from Alien. And just like Ellen Ripley, Ripley's doin' just fine. Ripley wasn't all for show, though.

It was decked out with sensors that would alert scientists on the ground to any forces that could be harmful or uncomfortable for a real astronaut. SpaceX hasn't released any data from Ripley yet, but from what we know, the launch seemed to go very well. Then, on Sunday morning, just over a day later, the crew capsule began firing its thrusters to dock with the Space Station.

And even though both objects were hurtling around the Earth at some 28,000 kilometers per hour, the docking was a success! So, shoutout to those SpaceX engineers for making that happen. Once the capsule safely attached to the dock, astronauts on board the Space Station opened the hatch and climbed in to collect air samples and unload the cargo, which included equipment and, like, a thousand packets of space food.

This mission marked a few exciting firsts. It was the first launch of a commercial crew capsule and the first time a commercial spacecraft docked on the Space Station. And although it had no humans on board this time, it was the also first time an American crew capsule had been launched from U.

S. soil since NASA retired the space shuttles in 2011. For SpaceX, it's a huge step forward in its mission to send humans to space and, ultimately, to Mars as well. Scientists will use the data they collect from Demo-1 to prepare for Demo-2, which will deliver two American astronauts to the Space Station as early as July.

Doesn't sound like much of a demo to me. This milestone really shows that we're entering into a new era in spaceflight. As commercial companies cut costs and build increasingly capable vessels, they're revolutionizing the way we explore space.

So someday, when a crew first touches down on Mars, it might be because of SpaceX or a company like it. And thanks to new results from missions like Mars Express, we know that there is a lot to learn once we get there. We don't have to stop learning things while we wait, though.

There's still a lot to discover about the universe, and that's why we're excited that this episode is supported by CuriosityStream. CuriosityStream is a subscription streaming service that offers over 2,000 documentaries and non­fiction titles from some of the world's best filmmakers, including exclusive originals. They have videos on everything from technology to lifestyles, and there's plenty of space content, too.

Like, there's one called Hubble's Imager that explains how scientists turn data from the Hubble Space Telescope into those beautiful, famous images, and what they can learn from them. Which is both aesthetically pleasing and very cool. You can get unlimited access to content like this starting at $2.99 a month.

And as a special “thank-you” for supporting SciShow, you can get the first 30 days for free! You just have to sign up at curiositystream.com/space and use the promo code “space” during the sign-up process. [♪ OUTRO].