Localized sources of water vapour on the dwarf planet (1) Ceres

The largest asteroid of the Solar System, (1) Ceres, has been thought to have an icy surface; here it is observed to be emitting water vapour. Water vapour on the asteroid Ceres The presence of hydrated minerals on the surface of Ceres, the largest body in the Solar System's main asteroid belt, suggested that there may be water there too. Now infrared spectra obtained by ESA's Herschel Space Observatory provide unambiguous evidence that there is water ice at or near the surface of Ceres. Water vapour is issuing at a rate of at least 10 26 molecules per second from sources on Ceres localized to mid-latitude regions. The water evaporation could be due to comet-like sublimation or to cryo-volcanism, in which volcanoes erupt volatiles such as water instead of molten rocks. This finding supports models that propose that the icy bodies such as comets may have migrated into the asteroid belt from beyond the notional 'snowline' dividing the early Solar System into a 'dry' inner and 'icy' outer regions. The ‘snowline’ conventionally divides Solar System objects into dry bodies, ranging out to the main asteroid belt, and icy bodies beyond the belt. Models suggest that some of the icy bodies may have migrated into the asteroid belt 1 . Recent observations indicate the presence of water ice on the surface of some asteroids 2 , 3 , 4 , with sublimation 5 a potential reason for the dust activity observed on others. Hydrated minerals have been found 6 , 7 , 8 on the surface of the largest object in the asteroid belt, the dwarf planet (1) Ceres, which is thought to be differentiated into a silicate core with an icy mantle 9 , 10 , 11 . The presence of water vapour around Ceres was suggested by a marginal detection of the photodissociation product of water, hydroxyl (ref. 12 ), but could not be confirmed by later, more sensitive observations 13 . Here we report the detection of water vapour around Ceres, with at least 10 26 molecules being produced per second, originating from localized sources that seem to be linked to mid-latitude regions on the surface 14 , 15 . The water evaporation could be due to comet-like sublimation or to cryo-volcanism, in which volcanoes erupt volatiles such as water instead of molten rocks.