Astronomers using the Herschel Space Observatory have detected water vapor on the dwarf planet Ceres, the biggest object in the main asteroid belt.
This is an artist’s impression of the dwarf planet Ceres. Image credit: NASA / JPL-Caltech.
Ceres is around 950 km across and was discovered on January 01, 1801 by the Sicilian astronomer Father Giuseppe Piazzi.
Astronomers thought it was a planet orbiting between Mars and Jupiter. Later, other cosmic bodies with similar orbits were found, marking the discovery of the asteroid belt.
Planetary researchers believe Ceres has a rocky inner core, an icy mantle, and a thin outer crust inferred from its density and rotation rate of 9 hours. The materials making up Ceres likely date from the first few million years of our Solar System’s existence and accumulated before the planets formed.
The dwarf planet Ceres as seen by Hubble Space Telescope. Image credit: NASA / ESA / SWRI / Cornell University / University of Maryland / STSci.
For the last century, Ceres was known as the largest asteroid in the Solar System. But in 2006, the International Astronomical Union reclassified Ceres as a dwarf planet because of its large size.
Until now, ice had been theorized to exist on Ceres but had not been detected conclusively. It took Herschel’s far-infrared vision to see, finally, a clear spectral signature of the water vapor.
“This is the first time water vapor has been unequivocally detected on Ceres or any other object in the asteroid belt and provides proof that Ceres has an icy surface and an atmosphere,” said Dr Michael Küppers from the European Space Astronomy Center in Spain, who is the lead author of a paper published in the journal Nature.
This graph shows variability in the intensity of the water absorption signal detected at Ceres by Herschel. The most intense readings correspond to two dark regions on the surface known as Piazzi and Region A, identified in the ground-based image of Ceres by Keck Observatory. The two data points at 110 degrees longitude were taken in a time interval of about 9 hours – equal to the Ceres rotation period – showing that variability in the water vapor production is possible even over short periods. Image credit: ESA, NASA, adapted from Kuppers et al.
The water evaporation could be due to comet-like sublimation (a portion of Ceres’ icy surface becomes warm enough to cause water vapor to escape in plumes at a rate of about 6 kg per second) or to cryo-volcanism, in which volcanoes erupt volatiles such as water instead of molten rocks.
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Michael Küppers et al. 2014. Localized sources of water vapour on the dwarf planet (1) Ceres. Nature 505, pp. 525–527; doi: 10.1038/nature12918
