Distinctive Elemental Composition of an Extrasolar Asteroid

Details Distinctive Elemental Composition of an Extrasolar Asteroid Distinctive Elemental Composition of an Extrasolar Asteroid

May 2009

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009aas...21430603k&link_type=abstract

American Astronomical Society, AAS Meeting #214, #306.03; Bulletin of the American Astronomical Society, Vol. 41, p.728

Astronomy and Astrophysics

Astronomy

Scientific paper

We present Keck+HIRES data with model atmosphere analysis of the helium-dominated polluted white dwarf, GD 40, in which we measure the atmospheric abundances of 9 elements: H, O, Mg, Si, Ca, Ti, Cr, Mn, and Fe. Apart from hydrogen whose origin is uncertain, this material accreted from a circumstellar reservoir, whose existence is demonstrated by excess infrared emission, and is most likely derived from an asteroid at least 1/10 of the mass of Ceres, the largest asteroid in our solar system. The data are consistent with rocky planetary material in which heavy elements are largely contained within oxides. We find n(Mg)/n(Si) = 3.3 +/- 1.3, appreciably larger than the ratio near unity for the bulk Earth, Mars, the Sun, and nearby stars, indicating that the primordial mix in this evolved planetary system has been altered within the parent body. One possibility is that the extrasolar asteroid experienced a substantial differentiation, such that silicon was concentrated in a crust and magnesium in a mantle, and that the crust has been subsequently lost. If so, then these data suggest that asteroid-scale differentiation has occurred in an extrasolar planetary system.
The work at UCLA has been partly supported by NASA and the NSF.

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