page_title: Dawn (spacecraft)
section_title: Scientific background
hierarchical_section_title: Dawn (spacecraft) / Scientific background
caption_attribution_description: English: PIA19547: Ceres RC3 Animation - Still Frame 25 http://photojournal.jpl.nasa.gov/catalog/PIA19547 http://www.jpl.nasa.gov/news/news.php?feature=4582 UPLOADER NOTE: Frame 25 of the original GIF animation (16.096KB) - via JASC Animation Shop v 2.02. In this closest-yet view of Ceres, the brightest spots within a crater in the northern hemisphere are revealed to be composed of many smaller spots. This frame is from an animation of sequences taken by NASA's Dawn spacecraft on May 4, 2015. This animation shows a sequence of images taken by NASA's Dawn spacecraft on May 4, 2015, from a distance of 8,400 miles (13,600 kilometers), in its RC3 mapping orbit. The image resolution is 0.8 mile (1.3 kilometers) per pixel. In this closest-yet view, the brightest spots within a crater in the northern hemisphere are revealed to be composed of many smaller spots. However, their exact nature remains unknown. Dawn's mission is managed by JPL for NASA's Science Mission Directorate in Washington. Dawn is a project of the directorate's Discovery Program, managed by NASA's Marshall Space Flight Center in Huntsville, Alabama. UCLA is responsible for overall Dawn mission science. Orbital ATK, Inc., in Dulles, Virginia, designed and built the spacecraft. The German Aerospace Center, the Max Planck Institute for Solar System Research, the Italian Space Agency and the Italian National Astrophysical Institute are international partners on the mission team. For a complete list of acknowledgements, visit http://dawn.jpl.nasa.gov/mission. For more information about the Dawn mission, visit http://dawn.jpl.nasa.gov.
context_page_description: Dawn is a retired space probe launched by NASA in September 2007 with the mission of studying two of the three known protoplanets of the asteroid belt, Vesta and Ceres. It was retired on November 1, 2018, and it is currently in an uncontrolled orbit around its second target, the dwarf planet Ceres. Dawn is the first spacecraft to orbit two extraterrestrial bodies, the first spacecraft to visit either Vesta or Ceres, and the first to orbit a dwarf planet, arriving at Ceres in March 2015, a few months before New Horizons flew by Pluto in July 2015.
  Dawn entered orbit around Vesta on July 16, 2011, and completed a 14-month survey mission before leaving for Ceres in late 2012. It then entered orbit around Ceres on March 6, 2015. NASA considered, but decided against, a proposal to visit a third target. On October 19, 2017, NASA announced that the mission would be extended until the probe's hydrazine fuel supply was used up. On November 1, 2018, NASA announced that the Dawn spacecraft had finally exhausted all of its hydrazine fuel, thus ending its mission. The satellite is currently in an uncontrolled state about Ceres.
context_section_description: The Dawn mission was designed to study two large bodies in the asteroid belt in order to answer questions about the formation of the Solar System, as well as to test the performance of its ion thrusters in deep space. Ceres and Vesta were chosen as two contrasting protoplanets, the first one apparently "wet" (i.e. icy and cold) and the other "dry" (i.e. rocky), whose accretion was terminated by the formation of Jupiter. The two bodies provide a bridge in scientific understanding between the formation of rocky planets and the icy bodies of the Solar System, and under what conditions a rocky planet can hold water.
  The International Astronomical Union (IAU) adopted a new definition of planet on August 24, 2006, which introduced the term "dwarf planet" for ellipsoidal worlds that were too small to qualify for planetary status by "clearing their orbital neighborhood" of other orbiting matter. Dawn is the first mission to study a dwarf planet, arriving at Ceres a few months before the arrival of the New Horizons probe at Pluto in July 2015.
  Ceres comprises a third of the total mass of the asteroid belt. Its spectral characteristics suggest a composition similar to that of a water-rich carbonaceous chondrite. Vesta, a smaller, water-poor achondritic asteroid comprising a tenth of the mass of the asteroid belt, has experienced significant heating and differentiation. It shows signs of a metallic core, a Mars-like density and lunar-like basaltic flows.
  Available evidence indicates that both bodies formed very early in the history of the Solar System, thereby retaining a record of events and processes from the time of the formation of the terrestrial planets. Radionuclide dating of pieces of meteorites thought to come from Vesta suggests that Vesta differentiated quickly, in three million years or less. Thermal evolution studies suggest that Ceres must have formed some time later, more than three million years after the formation of CAIs (the oldest known objects of Solar System origin).
  Moreover, Vesta appears to be the source of many smaller objects in the Solar System. Most (but not all) V-type near-Earth asteroids, and some outer main-belt asteroids, have spectra similar to Vesta, and are thus known as vestoids. Five percent of the meteoritic samples found on Earth, the howardite–eucrite–diogenite (HED) meteorites, are thought to be the result of a collision or collisions with Vesta.
  It is thought that Ceres may have a differentiated interior; its oblateness appears too small for an undifferentiated body, which indicates that it consists of a rocky core overlain with an icy mantle. There is a large collection of potential samples from Vesta accessible to scientists, in the form of over 1,400 HED meteorites, giving insight into Vesta geologic history and structure. Vesta is thought to consist of a metallic iron–nickel core, an overlying rocky olivine mantle and crust.
caption: Dawn image of Ceres from 13,600 km, May 4, 2015
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