A self-consistent model of the circumstellar debris created by a giant hypervelocity impact in the HD 172555 system

B. C. Johnson, C. M. Lisse, C. H. Chen, H. J. Melosh, M. C. Wyatt, P. Thebault, W. G. Henning, E. Gaidos, L. T. Elkins-Tanton, J. C. Bridges, A. Morlok

Research output: Contribution to journalArticlepeer-review

51 Scopus citations


Spectral modeling of the large infrared excess in the Spitzer IRS spectra of HD 172555 suggests that there is more than 1019 kg of submicron dust in the system. Using physical arguments and constraints from observations, we rule out the possibility of the infrared excess being created by a magma ocean planet or a circumplanetary disk or torus. We show that the infrared excess is consistent with a circumstellar debris disk or torus, located at 6 AU, that was created by a planetary scale hypervelocity impact. We find that radiation pressure should remove submicron dust from the debris disk in less than one year. However, the system's mid-infrared photometric flux, dominated by submicron grains, has been stable within 4% over the last 27 years, from the Infrared Astronomical Satellite (1983) to WISE (2010). Our new spectral modeling work and calculations of the radiation pressure on fine dust in HD 172555 provide a self-consistent explanation for this apparent contradiction. We also explore the unconfirmed claim that 1047 molecules of SiO vapor are needed to explain an emission feature at 8 μm in the Spitzer IRS spectrum of HD 172555. We find that unless there are 1048 atoms or 0.05 M ⊕ of atomic Si and O vapor in the system, SiO vapor should be destroyed by photo-dissociation in less than 0.2 years. We argue that a second plausible explanation for the 8 μm feature can be emission from solid SiO, which naturally occurs in submicron silicate "smokes" created by quickly condensing vaporized silicate.

Original languageEnglish (US)
Article number45
JournalAstrophysical Journal
Issue number1
StatePublished - Dec 10 2012
Externally publishedYes


  • astrochemistry
  • infrared: stars
  • planetary systems
  • planets and satellites: formation
  • radiation mechanisms: thermal
  • techniques: spectroscopic

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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