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We just mapped out 80% of our earth and gave the ISS a tuneup! Hank Green explains what is going on in this episode of SciShow Space News!

Hosted by: Hank Green
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Last week, scientists mapped one of the last truly unexplored parts of the solar system: the Earth's ocean floor. Until now, believe it or not, 80% of the seafloor had gone uncharted; that means that more than half of the Earth's topography was a mystery to us. In fact, we knew more about the topography of Mars, in a hundred times greater detail, than much of our own planet. But that's all changing with the ground-breaking new study released in the journal Science. 

Buried under thousands of meters of water and sediments, the ocean floor defies optical and radar-based exploration. In the past, we've studied it using sonar, which maps the seafloor by tracking echoes as they bounce back up to us. But this has to be done by boats, slowly skimming over tiny areas, and it takes forever. In the 1990's, a new method emerged, called "radar altimetry." Here a satellite takes radar measurements of the ocean's surface, which despite what you might think, isn't actually flat; it's covered in bumps and dips that mimic the topography of the ocean's floor. 

This is because the gravitational force of the seafloor varies slightly depending on its features. Formations, like huge underwater mountains, exert slightly more gravitation, which draws more molecules of water around it. This can create a shallow bump in the ocean's surface, up to 10cm high. 

Using this technique, a team lead by the Scripps Institution of Oceanography, used the altimeter on CryoSat-2, an ESA satellite designed to measure polar ice, to make a map of the ocean that's twice as accurate as the last one. CryoSat-2 can measure the ocean's surface to within a few centimeters. By averaging billions of measurements from CryoSat-2, with billions of measurements from NASA's JASON-1, another satellite equipped with an altimeter, the team came up with a more precise measurement than ever. And it revealed up to 20,000 new undersea volcanoes that we never knew existed, as well as new insights into the tectonics that govern the interactions between our oceans and continents.

They discovered two mid-ocean ridges where oceanic plates diverge and new crust forms: one that's now extinct, off the coast of Mexico, and one that's still active, off the coast of India. They also mapped fracture zones, kind of like stretchmarks on the seafloor that form as plates separate. The oceanographers traced them from South America to Africa, to show exactly where the continents drifted.

This new technology could revolutionize our ability to study our geologic history, as well as our understanding of how Earth works today. And also, we just discovered like 80% of our planet!

Now looking up, instead of down - have you ever wondered what it takes to go for a walk in space? On Tuesday morning, two astronauts: American, Reid Wiseman and German, Alexander Gerst, conducted NASA's second spacewalk of the year.

To prepare, they had to sleep overnight in an airlock that gradually decreased the air pressure from the normal 14.7 pounds per square inch aboard the ISS, to 10.2 pounds per square inch. This was to reduce the risk of decompression sickness, which can occur when the body enters a low pressure environment, like space, even when you're in a space suit. When you're exposed to really low pressures, gases like nitrogen, which are usually dissolved in your blood and body tissues, come out of solution and create problematic and painful gas bubbles. These bubbles can form in, or travel to, any part of the body, including the heart and brain, so astronauts have to keep them at bay.

So after spending all night in the airlock, Wiseman and Gerst then spent another few hours in their spacesuits, breathing pure oxygen, to slowly rid their tissues of any leftover inert gases like nitrogen. Finally they were ready to get to work, and spent about six hours repairing and installing equipment on the outside of the space station. They stayed connected to the station by giant tethers and moved around using jet thrusters on their backs, called Simplified Aids for Extra Vehicular Activity Rescue, or SAFERs. Thusly equipped, they first took out a worn-out pump and put it in the External Stowage Platform-2, which is to say, they put a broken pipe in the shed out back. Then they installed a new back-up power source for the mobile transporter; a sort of railcar system that moves machines around the space station.

Maybe it seems like changing a battery and taking out an old pump wouldn't be worth risking your lives for, but it's not like we can bring the ISS back to Earth for tune-ups. Besides, they're astronauts - they're hardcore. 

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