Abundant Circumstellar Silica Dust and SiO Gas Created by a Giant Hypervelocity Collision in the 12 Myr HD172555 System

Details Abundant Circumstellar Silica Dust and SiO Gas Created by a Giant Hypervelocity Collision in the 12 Myr HD172555 System Abundant Circumstellar Silica Dust and SiO Gas Created by a Giant Hypervelocity Collision in the 12 Myr HD172555 System

Sep 2009

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009dps....41.5506l&link_type=abstract

American Astronomical Society, DPS meeting #41, #55.06

Astronomy and Astrophysics

Astronomy

Scientific paper

We have used the IRS Spectrograph onboard the Spitzer Space Telescope to study the warm dust orbiting around the 29 pc distant β Pic analogue star HD172555. The dust mineralogy is very peculiar, composed primarily of highly refractory, non-equilibrium materials, with 3/4 of the Si atoms in silica (SiO2) species. Tektite and obsidian lab thermal emission spectra (non-equilibrium glassy silicas found in impact and magmatic systems) are required to fit the data. The best-fit model size distribution for the observed fine dust is dn/da = a-3.95±0.10. This steep a size distribution argues for a fresh source of material within the last 0.1 Myr. The location of the dust with respect to the star is at 5.8 ± 0.6 AU, within the terrestrial planet formation region but at the outer edge of any possible terrestrial habitability zone. The mass of fine dust is 4 x 1019 - 2 x 1020 kg, equivalent to a 150 - 200 km radius asteroid. Significant emission features centered at 4 and 8 µm due to fluorescing SiO gas are also found. Roughly 1022 kg of SiO gas, formed by vaporizing silicate rock, is also present in the system, and a separate population of very large, cool grains, massing 1021 - 1022 kg and equivalent to the largest sized asteroid currently found in the Solar System's main asteroid belt, dominates the solid circumstellar material by mass. The makeup of the observed dust and gas, and the noted lack of a dense circumstellar gas disk, strong primary x-ray activity, or an extended disk of β meteroids argues that the source of the observed circumstellar materials is a giant hypervelocity (> 10 km sec-1) impact between large rocky planetesimals, similar to the ones which formed the Moon and which stripped the surface crustal material off of Mercury's surface.

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