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The abundance of two of the three isotopes of oxygen have been measured in a comet by instruments on the Odin satellite, the L'Observatoire de Paris has announced. Comets consist of mixtures of ice and dust and are often described as dirty snowballs. When comets approach the Sun their ice begins to turn to gas, due to solar heating, and forms a tail millions of kilometres in length. The Odin satellite, launched in February, measured the isotopes in the water vapour in the atmosphere of comet Ikeya-Zhang (C/2002 C1) during its closest approach to the Earth (0.405 AU, 1 AU is the Sun-Earth distance) in April.
The oxygen isoptope measurements were performed by examining the spectral lines of water vapour at radio wavelengths and are the very first measurements of their kind. The results suggest that the ice in Ikeya-Zhang has similar abundances of the different oxygen isotopes as the Earth's oceans. Further measurements of oxygen isotopes in comets will provide valuable information on the relationship between water in asteroids, planets and ice in comets by which we can better understand the formation of our Solar System.
More info: L Observatoire de Paris
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