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Jan. 26, 2012: Is the Earth Normal?

Posted on Jan 26, 2012 in Seminars

Michael Jura

Knowing that extrasolar planetary systems are common, we would like to learn whether the Earth is normal or distinctive. Bulk Earth is 94% composed of O, Mg, Si and Fe and very deficient compared to the Sun in volatiles such as C and N. With our recent observations of white dwarf stars that have recently accreted tidally-disrupted minor planets that are about 300 km in diameter, we find a similar compositional pattern in extrasolar asteroids. While there must be individual exceptions, in aggregate, the studied extrasolar asteroids also are as “dry”; they probably formed interior to a snow line. Although the current sample is tiny, it appears that bulk Earth is compositionally normal for a rocky body. In the future, we may learn whether extrasolar planetesimals have undergone differentiation, a fundamentally important process in the history of our own planet.