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Dwarf planet Ceres is a long way from home
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IT’S an invader. Shiny spots and minerals on the surface of Ceres suggest that the asteroid belt’s largest object may have been born in the outer solar system, far from its current abode. This also hints that our current classification of comets, asteroids and planets is too simplistic. At 950 kilometres across, Ceres is considered a dwarf planet like Pluto, despite orbiting in the main asteroid belt between Mars and Jupiter. When NASA’s Dawn spacecraft arrived at Ceres in March, it saw that most of the dwarf is as dark as fresh asphalt, but that there are lighter spots in craters, which range from the brightness of concrete to that of ocean ice. New measurements suggest that the bright regions are mostly made of icy salt deposits, says Andreas
Nathues, lead investigator for Dawn’s camera team at the Max Planck Institute for Solar System Research in Munich, Germany. A large crater called Occator has an especially bright pit, which probably contains water ice that vaporises as Ceres rotates into sunlight. The vapour produces haze clouds that appear and disappear during Ceres’s 9-hour day. That makes Ceres the first large body in the asteroid belt to show such comet-like activity, blurring the line between comet and asteroid. The Dawn team thinks the ice originated beyond the solar system’s “snow line”, where water molecules condense. In the early solar system, this would have been several hundred million kilometres farther from the
NASA/JPL-Caltech/UCLA/MPS/DLR/IDA
Dwarf planet Ceres is a long way from home
spectrometer, she and her colleagues detected that minerals called ammoniated phyllosilicates make up about 10 per cent of Ceres’s surface. For these minerals to form, ammonia had to be incorporated as the dwarf planet formed – and ammonia ice is also only stable at the temperatures beyond the snow line (Nature, 10.1038/nature16172). Jupiter, Saturn, Uranus and Neptune probably moved a lot in the solar system’s early days, which could have sent objects like Ceres hurtling closer to the sun, says Chris Russell, –How I wonder what you are– Dawn’s principal investigator. “Ceres is right at that transition sun than Ceres’s current location, zone, where we’re moving from suggesting that the dwarf planet predominantly rocky bodies to was born in the land of comets and outer solar system objects that are migrated inwards later (Nature, predominantly water ice,” says Shane 10.1038/nature15754). Byrne at the University of Arizona in Other observations support this Tucson. Its mix of comet-like and idea, says Maria Cristina De Sanctis planet-like characteristics adds a new of the Italian National Institute of dimension to the debate about how to Astrophysics in Rome. Using Dawn’s define a planet. Rebecca Boyle n
Coming next week...
New scientist’s Bumper holiday special Secrets of the snowy owl The scary truth about fairy tales How to stack a dishwasher God vs the multiverse The awkward art of tipping And much, much more Don’t miss your copy
Joel Sartore
On sale from Wednesday 16 December
Plus: The 10 most exciting things happening in 2016 12 | NewScientist | 12 December 2015
IT’S an invader. Shiny spots and minerals on the surface of Ceres suggest that the asteroid belt’s largest object may have been born in the outer solar system, far from its current abode. This also hints that our current classification of comets, asteroids and planets is too simplistic. At 950 kilometres across, Ceres is considered a dwarf planet like Pluto, despite orbiting in the main asteroid belt between Mars and Jupiter. When NASA’s Dawn spacecraft arrived at Ceres in March, it saw that most of the dwarf is as dark as fresh asphalt, but that there are lighter spots in craters, which range from the brightness of concrete to that of ocean ice. New measurements suggest that the bright regions are mostly made of icy salt deposits, says Andreas
Nathues, lead investigator for Dawn’s camera team at the Max Planck Institute for Solar System Research in Munich, Germany. A large crater called Occator has an especially bright pit, which probably contains water ice that vaporises as Ceres rotates into sunlight. The vapour produces haze clouds that appear and disappear during Ceres’s 9-hour day. That makes Ceres the first large body in the asteroid belt to show such comet-like activity, blurring the line between comet and asteroid. The Dawn team thinks the ice originated beyond the solar system’s “snow line”, where water molecules condense. In the early solar system, this would have been several hundred million kilometres farther from the
NASA/JPL-Caltech/UCLA/MPS/DLR/IDA
Dwarf planet Ceres is a long way from home
spectrometer, she and her colleagues detected that minerals called ammoniated phyllosilicates make up about 10 per cent of Ceres’s surface. For these minerals to form, ammonia had to be incorporated as the dwarf planet formed – and ammonia ice is also only stable at the temperatures beyond the snow line (Nature, 10.1038/nature16172). Jupiter, Saturn, Uranus and Neptune probably moved a lot in the solar system’s early days, which could have sent objects like Ceres hurtling closer to the sun, says Chris Russell, –How I wonder what you are– Dawn’s principal investigator. “Ceres is right at that transition sun than Ceres’s current location, zone, where we’re moving from suggesting that the dwarf planet predominantly rocky bodies to was born in the land of comets and outer solar system objects that are migrated inwards later (Nature, predominantly water ice,” says Shane 10.1038/nature15754). Byrne at the University of Arizona in Other observations support this Tucson. Its mix of comet-like and idea, says Maria Cristina De Sanctis planet-like characteristics adds a new of the Italian National Institute of dimension to the debate about how to Astrophysics in Rome. Using Dawn’s define a planet. Rebecca Boyle n
Coming next week...
New scientist’s Bumper holiday special Secrets of the snowy owl The scary truth about fairy tales How to stack a dishwasher God vs the multiverse The awkward art of tipping And much, much more Don’t miss your copy
Joel Sartore
On sale from Wednesday 16 December
Plus: The 10 most exciting things happening in 2016 12 | NewScientist | 12 December 2015