This image is from the last sequence of images NASA's Dawn spacecraft obtained of the giant asteroid Vesta, looking down at Vesta's north pole as it was departing in 2012. Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA Image of Ceres showing the crater with the water-ice. Credit: NASA/JPL

The asteroid probe Dawn's mission is over. It is still probably in a low orbit around Ceres.    The probe was first launched Sept. 27, 2007.    Feb. 17, 2009: Mars Gravity Assist    July 16, 2011: Vesta Arrival. Vesta is a rocky world.    Sept. 5, 2017: Vesta Departure    March 5, 2015: Ceres Arrival    June 2016: End of prime mission    July 2016: Start of first extended mission    October 2017: Start of second extended mission    Nov. 1, 2018: End of Mission    While in orbit, the probe learned that the inner solar system’s only dwarf planet, albeit never fully differentiated, was an ocean world where water and ammonia of unknown provenance reacted with silicate rocks. As the ocean world froze and sublimed into space, salts and other telltale minerals concentrated into deposits that are now exposed vividly in many locations across the surface, awaiting easy sampling by future missions.    By analyzing data collected near the end of the mission, Dawn scientists have concluded that the liquid in the crater came from a deep reservoir of brine, or salt-enriched water inside the asteroid. By studying Ceres' gravity, scientists learned more about the dwarf planet's internal structure and were able to determine that the brine reservoir is about 25 miles (40 kilometers) deep and hundreds of miles wide.    In early June 2018, it fired its engine for the last time, to move into a lower orbit around the asteroid Ceres. This orbit is less than 30 miles (50 kilometers) above the surface of Ceres -- 10 times closer than the spacecraft had ever been.    Dawn collected gamma ray and neutron spectra, which help scientists understand variations in the chemical makeup of Ceres' uppermost layer. That very low orbit garnered some of Dawn's closest images yet.    Powered by an efficient ion engine, Dawn was the first mission to orbit a main belt asteroid. And it was the first to visit a dwarf planet and orbit two targets on a single mission.

This simulated perspective view shows Occator Crater, measuring 57 miles (92 kilometers) across and 2.5 miles (4 kilometers) deep, which contains the brightest area on Ceres. This region has been the subject of intense interest since Dawn's approach to the dwarf planet in early 2015. This view, which faces north, was made using images from Dawn's low-altitude mapping orbit, 240 miles (385 kilometers) above Ceres. Image credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA

Nov. 1, 2018: NASA's Dawn spacecraft went silent, ending a historic mission that studied time capsules from the solar system's earliest chapter.    Dawn missed scheduled communications sessions with NASA's Deep Space Network Wednesday, Oct. 31, and Thursday, Nov. 1. After the flight team eliminated other possible causes for the missed communications, mission managers concluded that the spacecraft finally ran out of hydrazine, the fuel that enables the spacecraft to control its positioning so it can communicate with Earth.    The Dawn spacecraft launched in 2007 and completed an extended mission to explore the two largest objects in the main asteroid belt—asteroid Vesta and dwarf planet Ceres. The inert spacecraft will remain orbit around Ceres for decades.

This artist concept shows NASA's Dawn spacecraft in fully operational mode with its solar panels extended.Image credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA

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