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Uploaded:2014-10-23
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SciShow Space News takes you to the solar system’s own Death Star -- Saturn’s moon Mimas, where something mysterious is going on. Plus, we share a stunning new photo from the Hubble Space Telescope that holds a few surprises!

Hosted by: Caitlin Hofmeister
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Sources:
http://news.sciencemag.org/space/2014/10/does-mimas-have-ocean-under-icy-cap
http://www.eurekalert.org/jrnls/sci/emb_scipak/pdf/tajeddine141017.pdf
https://cornell.app.box.com/mimas
http://hubblesite.org/newscenter/archive/releases/2014/39/full/
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Of Saturn's 62 moons, the one called Mimas has a reputation for two things--1) being the object in space that most looks like the Death Star, and 2) being the most boring body in the Solar System.

But last week, astronomers discovered that Mimas may be a lot more exciting than we originally thought. With a diameter of just 396 km, the moon is small, with about the same surface area as Spain, and apart from its super laser-like Herschel Crater, it looks pretty unremarkable, a near perfect sphere with no sign of geological activity.

But as we all know, sometimes the most normal looking things, or even people, are actually the weirdest. That's what a team of astronomers led by Cornell University learned when they used a technique called stereophotogrammetry to study Saturn's moons.

They used hundreds of images taken by NASA's Cassini Spacecraft at different times and from different angles to create precise, 3D maps of the moons and their orbits, and they realized there's something weird about Mimas, it had a libration, or a wobble.

As a moon rotates on its axis, the gravitational pull from its planet is more or less constant, but if one side of the moon is more massive, that side will get a little extra pull when it faces the planet, creating a wobble, like a lopsided top. The thing is, despite its giant crater, Mimas is mostly symmetrical, but because it has this wobble, it must not be as symmetrical as it looks. So astronomers figure the difference must be under the moon's surface.

Using computer models built around the exact same size and nature of Mimas's libration, they came up with two possible explanations: one is that Mimas's dense core isn't spherical but is elongated kind of like a rugby ball. The core could have formed this way if Mimas had originally taken shape when it was much closer to Saturn, where the planet's gravity is strong enough to actually stretch the rock. Then, Mimas could have accumulated its nice, spherical crust after it moved outward, farther away from the reach of Saturn's gravity.

But that begs a couple of questions, like why would the moon have moved? And why is there no visible sign of an asymmetrical core, like a protruding lump sticking out somewhere? This stumped the astronomers, so they came up with another explanation: maybe Mimas is full of water. The team took their inspiration for this idea from eggs. If you spin an egg on a table, you can tell if it's raw or hard-boiled. The raw egg, with a liquid interior, will wobble as its insides slosh around. An ocean about 30 km under the surface could have the same effect on Mimas.

Now, the moon's crater surface shows no signs of ever having seen liquid water and it seems way too cold to have a liquid ocean, but Saturn's gravity could produce enough tidal friction, the sort of gravitational tug of war that goes on as a moon orbits its planet, to keep a subsurface ocean from freezing, the same way it does on Enceladus. If Mimas does have water beneath its surface, we can add it to the growing list of moons in our solar system that could possibly harbor life. If not, there's still something really mysterious going on. The team hopes to get more clues in 2016 when Cassini will pass near Mimas again and take more images.

And speaking of images, check out the latest from Hubble. This is the massive galaxy cluster Abell 2744, also known as Pandora's Cluster. But it's actually four galaxy clusters slowly merging, tens of thousands of individual galaxies with a combined mass of about a thousand times that of the Milky Way. It's so huge that it literally bends light.

Thanks to a German patent clerk named Albert Einstein, we know that matter warps space and time around it, the way a ball creates a dimple in a bed sheet. So an object with enough mass can bend the light that's traveling through the space that surrounds it, creating the effect of a lens, curving light around the object and focusing it, more or less, on the other side.

This, we know, is gravitational lensing, and it's how Pandora's Cluster serves as a kind of magnifying glass to see far into space. And it's also what led to an exciting surprise in this image, the discovery of one of the most distant galaxies ever detected.

Far, far beyond Panodra's Cluster, about 13 billion light years away, this newly found galaxy is about 500 times smaller than the Milky Way. We can only see it in this picture because Pandora's Cluster magnified it to look about 10 times larger and brighter. Since the light from this galaxy has taken 13 billion years to get here, this image is really a peek into the distant past, shortly after the Big Bang 13.8 billion years ago. So the small, fuzzy blob you see here may be what galaxies looked like when the universe itself was young.

Thank you for watching this episode of SciShow Space News. If you wanna make sure you keep up with the latest events around the universe, check out subbable.com/scishow to learn how you can help support us. And don't forget to go to youtube.com/scishowspace and subscribe.

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