NASA’s Dawn spacecraft captured pictures in visible and infrared wavelengths, which were combined to create this false-color view of a region in 57-mile-wide (92-kilometer-wide) Occator Crater on the dwarf planet Ceres (in the main asteroid belt between Mars and Jupiter). Here, recently exposed brine, or salty liquids, in the center of the crater were pushed up from a deep reservoir below Ceres’ crust. In this view, they appear reddish.
Seen here is Cerealia Facula (“facula” means bright area), a 9-mile-wide (15-kilometer-wide) region with a composition dominated by salts. The central dome, Cerealia Tholus, is about 1.9 miles (3 kilometers) across at its base and 1,100 feet (340 meters) tall. The dome is inside a central depression about 3,000 feet (900 meters) deep.
Dawn’s mission is managed by NASA’s Jet Propulsion Laboratory, a division of Caltech, for the agency’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. JPL is responsible for overall Dawn mission science. Northrop Grumman in Dulles, Virginia, designed and built the spacecraft. The German Aerospace Center, Max Planck Institute for Solar System Research, Italian Space Agency and Italian National Astrophysical Institute are international partners on the mission team.
“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 drive 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.”
“NASA’s Dawn spacecraft turned science fiction into science fact by using ion propulsion to explore the two largest bodies in the main asteroid belt, Vesta and Ceres. The mission will end this fall, when the spacecraft runs out of hydrazine, which keeps it oriented and in communication with Earth.”
“Occator Crater on Ceres is home to the brightest area on the entire dwarf planet. At 57 miles (92 kilometers) wide and 2.5 miles (4 kilometers) deep, Occator displays evidence of recent geologic activity. NASA’s Dawn mission found that the bright spots may have been produced by upwelling of salt-rich liquids after the impact that formed the crater. Pan and zoom as you fly over the crater with Dawn in this 360-degree animation made with observations from the spacecraft.”
“Dawn delves into the unknown and achieves what’s never been attempted before. A mission in NASA’s Discovery Program, Dawn orbited and explored the giant protoplanet Vesta in 2011-2012, and now it is in orbit and exploring a second new world, dwarf planet Ceres.
Dawn’s goal is to characterize the conditions and processes of its earliest history by investigating in detail two of the largest protoplanets remaining intact since their formation. Ceres and Vesta reside in the main asteroid belt, the extensive region between Mars and Jupiter, along with many other smaller bodies. Each followed a very different evolutionary path, constrained by the diversity of processes that operated during the first few million years of solar system evolution. When Dawn visits Ceres and Vesta, the spacecraft steps us back in solar system time.”
“Dwarf planet Ceres is shown in these false-color renderings, which highlight differences in surface materials. Images from NASA’s Dawn spacecraft were used to create a movie of Ceres rotating, followed by a flyover view of Occator Crater, home of Ceres’ brightest area.”
“Ceres (minor-planet designation: 1 Ceres) is the largest object in the asteroid belt, which lies between the orbits of Mars and Jupiter. Its diameter is approximately 945 kilometers (587 miles), making it the largest of the minor planets within the orbit of Neptune. The thirty-third-largest known body in the Solar System, it is the only one identified orbiting entirely within the orbit of Neptune that is a dwarf planet. Composed of rock and ice, Ceres is estimated to comprise approximately one third of the mass of the entire asteroid belt. Ceres is the only object in the asteroid belt known to be rounded by its own gravity. From Earth, the apparent magnitude of Ceres ranges from 6.7 to 9.3, and hence even at its brightest, it is too dim to be seen with the naked eye, except under extremely dark skies.
Ceres was the first asteroid discovered, by Giuseppe Piazzi at Palermo on 1 January 1801. It was originally considered a planet, but was reclassified as an asteroid in the 1850s when many other objects in similar orbits were discovered.
Ceres appears to be differentiated into a rocky core and icy mantle, and may have a remnant internal ocean of liquid water under the layer of ice. The surface is probably a mixture of water ice and various hydrated minerals such as carbonates and clay. In January 2014, emissions of water vapor were detected from several regions of Ceres. This was unexpected, because large bodies in the asteroid belt do not typically emit vapor, a hallmark of comets.
The robotic NASA spacecraft Dawn entered orbit around Ceres on 6 March 2015. Pictures with a resolution previously unattained were taken during imaging sessions starting in January 2015 as Dawn approached Ceres, showing a cratered surface. Two distinct bright spots (or high-albedo features) inside a crater (different from the bright spots observed in earlier Hubble images) were seen in a 19 February 2015 image, leading to speculation about a possible cryovolcanic origin or outgassing. On 3 March 2015, a NASA spokesperson said the spots are consistent with highly reflective materials containing ice or salts, but that cryovolcanism is unlikely. On 11 May 2015, NASA released a higher-resolution image showing that, instead of one or two spots, there are actually several. On 9 December 2015, NASA scientists reported that the bright spots on Ceres may be related to a type of salt, particularly a form of brine containing magnesium sulfate hexahydrite (MgSO4·6H2O); the spots were also found to be associated with ammonia-rich clays.”
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