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Hank Green: Okay, first we're gonna start off this episode by, uh, everybody taking your hands and putting them on the side of your head and holding tight. What if I told you that there's a place in our solar system that's covered in oceans and has an atmosphere full of oxygen and it's not Earth? [intro music] I'm sorry if your mind just broke in half, but that's why I was warning you. But don't take your hands down yet! Let me, while you're holding your brain together, take you to the place that I'm talking about: Europa, the sixth moon of Jupiter. Europa has turned out to be one of those places, like Spokane, Washington, or Tumblr, that seems pretty cool at first, but the more time you spend there the awesomer it gets. Case in point, Galileo first discovered Europa in 1610, and it was the first moon outside of our moon to be discovered, so the big news then was, "Oh my gosh! Other planets have things orbiting them." That was a big deal back then, what with the Earth supposedly being the center of the universe. So Europa didn't get a ton of attention for the next, say, 400 years or so, until astronomers started to get a little bit more data. After staring at Europa from Earth-based observatories for a while, finally got some spacecraft out there to look at it -- first Voyager and then the Galileo spacecraft, and, you know, Hubble pitched in as well, and we've been able to discover four, sort of, mind-breakingly awesome things about Europa. Thing number one: Europa's surface was as smooth as a baby's bottom (well, if a baby's bottom has cracks several miles wide in it, but if you looked really close, a baby's bottom would have cracks several miles wide in it). It turns out that its surface is the smoothest in the solar system. Thing number two: Europa's surface was also highly reflective, a lot like the surface of, say, a frozen lake, and it even absorbed a lot of the same wavelengths of infrared light that ice does. Like water ice. See? Huh? Do you see where I'm going? Thing number three: In the 1990s, Hubble detected that Europa has a very thin, tenuous atmosphere made up mainly of molecular oxygen. And thing number four: The Galileo probe found out that Europa also has a faint magnetic signature that it picks up from Jupiter's magnetic field -- but -- BUT -- that signature could only be created if Europa were covered with something that conducted electricity, much like salt water does. I know! We're talking about a place that's covered with frozen water, it has a tenuous oxygen atmosphere, and even though it's 485 million miles from the Sun, it's actually not that cold. Turns out, Europa is caught in this constant gravitational tug-of-war between the planet Jupiter and its sister moons Io and Ganymede, and that gravitational tug-of-war creates friction on Europa, meaning that its sub-surface are probably quite warm and liquid. I mean, what more do you need? It's got oxygen, it's got water (though it's mostly frozen).... I mean, it's practically Milwaukee. So, it's got all this stuff, so it must have life, right? I mean, it probably has a frickin' minor league baseball team. The answer to both of those questions, of course, is that we don't know (well actually, I'm pretty sure that there's no baseball anywhere else in the universe except on Earth, 'cause it's just a weird sport). What we do know is that there's life here on Earth that can survive in really extreme environments, and if we took them to Europa they might actually do okay. So this is why Europa is at the top of the list, along with Mars and Titan and downtown Detroit, as really promising places to look for life. And of course, because this could be the greatest scientific discovery of all time, NASA and the European Space Agency have plans to go and try and find that life that may be on Europa. They've talked about landing spacecraft on the surface of Europa. They've also talked about bringing, like, a nuclear power device that would melt its way through the ice and then go swimming. But with, you know, budget crunches, unless you personally have a couple billion dollars lying around you want to donate to the cause, it's not gonna happen any time soon. Okay, I'm done blowing your mind. You can put your hands down now. Your mind should be safe for the rest of the day, and if you want more of this, please subscribe to SciShow. If you want to know more about Europa, there are links in the description, and if you want to give us tips, ask questions, or tell us what to talk about in the future on SciShow, you can get to us on Facebook and Twitter and of course in the YouTube comments below. [endscreen]