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2018-11-01. After visits with Vesta and Ceres, asteroid-exploring Dawn spacecraft goes dark.

posted Nov 4, 2018, 7:47 PM by Alan Gould

By Paul Voosen, Science Magazine. [https://www.sciencemag.org/news/2018/10/after-visits-vesta-and-ceres-asteroid-exploring-dawn-spacecraft-about-go-dark] For GSS A Changing Cosmos chapter 7. Excerpt: ...After several missed attempts to communicate with Dawn over the past 2 days, NASA declared that the spacecraft had run out of hydrazine and reached the end of its mission. ...[original coverage from 17 October]: ...After an 11-year journey to Vesta and Ceres, the asteroid belt's two largest members, NASA's Dawn spacecraft ... gave a close-up view of how the presence or absence of water can shape asteroids, will remain tumbling in orbit around Ceres for decades before ultimately crashing into it. Launched in 2007, Dawn is the only NASA mission to orbit two planetary bodies, a feat made possible by its efficient ion thrusters. In 2011, it arrived at the egg-shaped, 600-kilometer-long Vesta, orbiting for a year before departing for Ceres, where it arrived in 2015. ...The two asteroids, which together account for 45% of the belt's mass, turned out to be a tale of contrasts. Parched Vesta has a composition like the terrestrial planets, with an iron core and a dry, rocky surface carved up into canyons, craters, and mountains, remnants of past impacts and volcanism. Dawn was able to verify that a class of meteorites found on Earth are chips off of Vesta, making it a sort of "reverse sample return mission," says Carol Raymond, the mission's principal investigator and a planetary scientist at NASA's Jet Propulsion Laboratory (JPL) in Pasadena, California. Telescopes had already found water-rich minerals on Ceres, a 900-kilometer-wide body classified as a dwarf planet because of its large size and spherical shape. Dawn revealed the remnants of a frozen ocean topped by a heavily cratered crust of clays and salts. ...In its final months, Dawn settled into a tight orbit, just 35 kilometers from Ceres's surface. The defunct craft could remain in orbit for a half-century or more....  


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