Hank: Welcome back to SciShow Breaking News, I'm Hank Green. In a couple of days, we will be sharing a special episode of SciShow News dedicated to the great minds of science that left this mortal coil in 2012, but before then, I want to tell you about a couple of man-made geniuses that we'll be losing in a couple of days. And they will be doing themselves in at our command. (Intro plays) For around 340 days, two twin probes known as Ebb and Flow have been orbiting the moon, giving us the most detailed look at our lone natural satellite since people last walked on its surface in 1972. Working together is part of the GRAIL mission, which stands for Gravity Recovery and Interior Laboratory, the probes entered orbit around the moon on New Year's Day of 2012, tasked with created the first high-resolution map of the moon's gravitational field, because yeah, even though we look at the moon every day and people have, like, played golf on it, we still don't know a lot of things about the moon, like how it formed and what its composition is. By mapping its gravity, we can learn about its density, which in turn yields clues about what's inside. Thanks to Ebb and Flow, we now know a lot more about our celestial little brother, including that its crust is much thinner than scientists assumed about 34-43 kilometers thick, and that its composition is surprisingly earth-like, with the same proportion of aluminum in its crust, for example. All this supports the theory that the moon formed from fragments of earth stuff that were thrown into orbit after a planet-sized body slammed into baby earth, some 4.5 billion years ago. And there's more GRAIL science to come as researchers will continue to pore over the data the orbiters have sent back, but with their mission accomplished and only a few days of fuel left, Ebb and Flow will be given one final instruction--to aim themselves directly toward the lunar surface and fire their thrusters. The probes are scheduled to make impact this Monday, December 17th at 2:28 Eastern Time in the US. You can learn more about GRAIL and the moon and how Ebb and Flow will go out in style in the links below, and there will be a press conference on Thursday the 13th to discuss the impacts of these impacts, but for now, I bid farewell to these two explorers, so long and thanks for all the data. Thank you for watching this episode of SciShow, if you want to keep up to date on all the latest breaking news in science, you can go to youtube.com/scishow and subscribe. (Endscreen)