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This week on SciShow Space News, Saturn’s moon Enceladus probably has a giant ocean covering the entire world. And the year-long mission to the International Space Station just hit its halfway point!

Hosted by: Caitlin Hofmeister
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Space Station Live: First 100 Days of the One Year Mission:
If there's anything that we're becoming more and more aware of as we study the solar system, it's that water is everywhere.  Seriously, we just keep finding the stuff.  And according to a new study published by the journal Icarus, it seems that there's a whole lot of it on Saturn's moon Enceladus.  A global ocean making up a layer beneath the crust that covers the entire moon.

Although no one's quite sure how it got there.  The Cassini Probe reached the Saturnian System in 2004, and by 2005 it had detected plumes of water vapor coming from Enceladus' South Pole.  And vapor plumes are a sign of something important--chemically active geology, because something is making the moon gush water vapor.
They probably mean there's liquid water around too, but exactly how much water is on Enceladus has been an open question ever since.

The moon is covered in an icy crust and it's hard to figure out what's happening below the surface without actually landing there for a closer look.  So, scientists have had to find some more indirect clues.  Previous studies modelled the moon's insides based on the effects of tidal heating, where the friction caused by the gravitational pull of Saturn could have generated enough heat to melt some of the ice into water.  But that would have only accounted for a smaller ocean near the South Pole. 

Now, a group of American researchers has taken a look at seven years' worth of Cassini data and concluded that there must be a layer of ocean covering the entire moon.  They built their model based on the moon's libration, a measure of how much it wobbles in its rotation and in its orbit around Saturn.  Liquid water sloshes around, leading to more wobbling.  And according to the team's calculations, Enceladus has a layer of liquid sandwiched between its rocky core and its icy crust. 

This liquid is probably between 26 and 31 kilometers deep, about 6-8 times as deep as the average ocean here on Earth.  Not bad for a moon the width of Arizona.  

Researchers still have a lot of work ahead of them, because they haven't figured out how Enceladus could have produced enough heat, to melt all that ice.  From our current understanding of tidal heating, it wouldn't be enough, so scientists may have to rethink how the whole process works.  

Still, these new results are pretty exciting, and for good reason.  Confirming that there's more water, and hopefully chemical activity to go along with it, make it more likely that wet worlds like Enceladus could have the ingredients to harbor life.  And if so many worlds within our solar system have those ingredients, there are probably a lot more out there in the universe that do too.

But, so far within our solar system, there's only one place besides Earth that we know has life--the International Space Station.  And two of its crew members have just reached an important milestone, Astronaut Scott Kelly and Cosmonaut Mikhail Kornienko, just reached the halfway point of their year long mission.  That's about twice as long as the typical space station visit, and so far they say it's going well.

Their extended stay is being used to study the effects of long term space travel, like muscle weakening and bone loss, data that will be used to help plan future missions to Mars.  We won't know most of the results until the two come home, but according to Kelly, we've already learned somethings about astronaut psychology.

For example, one issue Kelly had the last time he was in space, for a five-month mission, was a general decrease in motivation and productivity about one hundred days into the trip.  It's a well known problem called the third quarter phenomenon, where being isolated in a small space tends to make people stop performing well during the third quarter of their missions, probably because the end is in sight.  And it's something that astronauts and their space agencies are working to fix; both for the sake of the crew's mental health and because being extra productive means more science can get done.

But since only four people have been in space for a full year straight, we've had few opportunities to study the third quarter of a year-long mission, as opposed to a five or six month one.  And scientists still weren't sure if the problem would happen around a hundred days in space, no matter how long the mission.  But this time, after his first hundred days in space, Kelly said he wasn't feeling the same decline in productivity, which is promising.  Considering a mission to Mars would take two years or more, nobody wants their astronauts to start feeling burned out after just three and a half months.

So far, most of Kelly and Kornienko's experiences are in line with what scientists have come to expect from a six-month mission.  It's the next half of the year that makes this mission so special.  But it also means we'll have to wait another six months for most of the results, including how being in space so long affects astronaut's stamina.

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