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The icy surface of a comet will soon get smacked by a spacecraft named Rosetta. Rosetta has been orbiting the comet for more than two years. And as NPR's Nell Greenfieldboyce reports, this historic mission is about to come to a dramatic end.
NELL GREENFIELDBOYCE, BYLINE: Matt Taylor is the mission's project scientist at the European Space Agency, and he doesn't know how he'll feel tomorrow morning when Rosetta plunges down to the comet.
MATT TAYLOR: There's mixed emotions here. You know, it's people who have invested their lives and their mentality I think as well, their psychology on this mission.
GREENFIELDBOYCE: Previous missions just flew by comets quickly. But in the 1980s, researchers began dreaming of doing an in-depth study by traveling along with one of these cosmic ice balls. Rosetta launched in 2004. It traveled for 10 years and about 4 billion miles to catch up with the comet. In 2014, it finally slipped into orbit.
TAYLOR: It was an adventure. It was doing something daring. It was doing something ridiculous, in fact. We're flying around a comet.
GREENFIELDBOYCE: A few months later, Rosetta achieved another historic first. It deployed a washing-machine-sized probe called Philae that touched down on the comet's surface.
GREENFIELDBOYCE: Controllers in Germany went crazy with joy, but then they realized that Philae's anchors had failed. Philae bounced a couple of times and ended up in some shadowy crevice that kept sunlight from its solar panels. Its exact resting place was only spotted a few weeks ago in a photo taken by Rosetta.
TAYLOR: Psychologically it was a great relief to have an unambiguous identification of the location of the lander.
GREENFIELDBOYCE: The lander did live for a few days - long enough to gather unprecedented images and data. Paul Weissman is a mission scientist with the Planetary Science Institute.
PAUL WEISSMAN: You have to, you know, look at the glass as being half full not half empty. On the whole I think it was a tremendous success.
GREENFIELDBOYCE: He says comets are fascinating because they're the leftovers from the process that formed earth and the other planets, and they basically haven't changed in 4 and a half billion years.
WEISSMAN: Comets are the best preserved samples of solar system material from the origin.
GREENFIELDBOYCE: This particular comet is shaped sort of like a rubber duck. Rosetta's grand finale will put it in a freefall towards the duck's head. It will send back data and images in real time all the way down. Weissman says the end won't be a spectacular explosion. Rosetta will be going pretty slow - about the speed of a person walking.
WEISSMAN: Imagine yourself walking into a wall. It wouldn't damage you very much.
GREENFIELDBOYCE: But the spacecraft will tilt. Its antenna will stop pointing at Earth, and Rosetta will go silent. Nell Greenfieldboyce, NPR News.
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