24 February 2005
Earth and Venus part company
The Mariner and Venera probes sent to Venus in the 1960s and 1970s revealed many differences between the venusian atmosphere and that on Earth. One of the hardest to account for is the preponderance of noble gases on Venus, in particular an argon-36 level 50 times higher than on Earth. A new theory tracks the cause of this difference to around 4.5 billion years ago, when Earth and Venus are thought to have grown as a result of collisions between several Mars-sized planets. Numerical simulations show that when a giant impact occurs, the presence of an ocean drastically increases the rate at which atmosphere is lost. On Earth, almost all the proto-atmosphere accrued during planet formation would have been stripped away during collisions. Venus, nearer the Sun, is unlikely to have had a major ocean, and its proto-atmosphere would have survived.
Enhanced atmospheric loss on protoplanets at the giant impact phase in the presence of oceans
HIDENORI GENDA & YUTAKA ABE
Nature 433, 842–844 (2005); doi:10.1038/nature03360
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100 and 50 years ago
Nature 433, 814 (2005); doi:10.1038/433814a
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