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This week's space news isn't so much about exciting things in space as it is about things that were once in space coming down to Earth.  The first thing is actually a pair of people, and all of us from scientists to civilians are excited to welcome home.  The other thing is a high energy meteoroid that almost nobody noticed.  But let's start with the people.

American astronaut Scott Kelly and Russian cosmonaut Mikhail Kornienko came back to Earth on Tuesday, March 1st after a nearly one year, or to be precise, 340 day, mission on the ISS.  Kelly set the record for the longest time a US astronaut has been in space, and while he was up there, he did everything from eating the first space-grown lettuce to conducting important space walks to maintain the ISS.  But the main goal of his yearlong mission was to see how human bodies respond to being in space for a long time, both biologically and physiologically, especially when it comes to the effects of weightlessness and radiation.  

For example, in space, body fluids shift around and get redistributed in their tissues.  This includes brain fluids, which can affect an astronaut's optic nerves and eyes and impair their vision.  With effects like this in mind, scientists will use medical data from before, during, and after the mission to better plan for future long term space projects.  Like, eventually, missions to Mars, which will probably take over a year of space flight time alone, and the really cool thing for researchers is Scott Kelly is an identical twin.  So while he's been living up on the ISS for a year, his genetically identical brother, Mark Kelly, has been living a relatively normal life here on Earth, which means that NASA scientists have an experimental and a control set of data to analyze and contrast, to really see what subtle effects a year in space can have on a person's body.  They're calling this experiment, wait for it, the Twins Study.  Scientists will use biological samples like blood, urine, and saliva, plus other tests, to investigate the effects on human physiology, behavior, and decision making.  They'll also compare the brothers' gut microbiomes and things like proteins and metabolites to see if there were any changes to the way Scott Kelly's cells expressed genes while in space.  Researchers will start analyzing massive amounts of data from Kelly and Kornienko right away, but it could be months or even years before NASA publishes any significant results.  So for now, let's let those guys rest in the nice, comfy, full-gravity environment of home and enjoy their job well done.

Now for another thing.  On February 6th, a chunk of space rock apparently exploded about 30km over the Atlantic Ocean, releasing the same amount of energy as 13,000 tons of TNT.  The catch?  Nobody really seemed to know anything about it, at least, at first.  It's the largest atmospheric impact since the Chelyabinsk meteor explosion over Russia in February of 2013, which, if you remember, was strong enough to shatter glass and cause injuries, but that explosion was equivalent to 500,000 tons of TNT.  So by comparison, this latest explosion was pretty small and it happened over the Atlantic Ocean, about 1,000 km off the coast of Brazil instead of over a populated area, so any pieces would have fallen right into the water.

It would have been a dramatic sight to see, but it doesn't look like anyone saw it.  So how do we know it happened?  Did it even happen?  If a meteor explodes in the atmosphere and no one's around to see it...yes, it happened.  Well, the data originally came from the US government, most likely military satellite observations.  The information was then published on NASA's Fireball and Bolide Reports website, recording things like the time, place, trajectory, and explosive energy released.  It makes sense that satellites would be monitoring for such large chunks of space debris, but it's not surprising that an event like this wouldn't be widely reported.  

Earth's atmosphere is constantly being buffeted by around 100 tons of space debris a day, but most of the stuff is small and burns up way before it reaches the ground.  Some of these chunks even burn bright enough that we can see them as meteors from where we're standing, the so-called shooting stars.  But really huge meteoroids, the ones that cause damage, are very few and far between.  So it's probably a good thing that you didn't know about the Atlantic meteoroid, 'cause when it comes to things hitting the Earth, hitting people, big space objects, no news is good news.

Thanks for watching this episode of SciShow Space News, and thank you especially to all of Patrons on Patreon who make this show possible.  If you wanna help us keep making episodes like this, you can go to Patreon.com/SciShow and don't forget to go to YouTube.com/SciShowSpace and subscribe.  

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