While you were sleeping, a truly massive undertaking got under way, one that the BBC terms "one of the most ambitious space missions in history." Europe's Gaia satellite—which has been two decades in the making—launched at 4:12am EST today, setting it on a course to essentially inventory the Milky Way and create a 3D map of it, reports Space.com. The satellite will be tasked with logging the positions and distances to some 1 billion stars—that's 1% of the stars in the galaxy—but it's expected to turn up much more. Its sophisticated instruments (among them, a 1 billion-pixel camera) should facilitate the discovery of unknown asteroids, comets, dead stars, and even planets, reports the BBC. The end result: The most realistic understanding yet of how the Milky Way was assembled.
The European Space Agency describes the process: Each star will be reviewed an average 70 times over a five-year period, with Gaia measuring the distance of the star from the sun (along with properties like brightness, temperature, and chemical composition) as it moves around the sun. The repeat measurements will allow Gaia to map the brightest stars' coordinates to within seven micro-arcseconds, which an ESA official describes as an angle "equivalent to the size of a euro coin on the Moon as seen from Earth." Space.com notes that the ESA launched a previous star-mapping mission in 1989; that satellite, Hipparcos, could measure the distances of bright stars within 3,250 light-years with a modest margin of error. Gaia will be able to measure up to 32,500 light-years away.