Spectral properties and composition of potentially hazardous Asteroid (99942) Apophis

Richard P. Binzel, Andrew S. Rivkin, Cristina A. Thomas, Pierre Vernazza, Thomas H. Burbine, Francesca E. DeMeo, Schelte J. Bus, Alan T. Tokunaga, Mirel Birlan

Research output: Contribution to journalArticlepeer-review

71 Scopus citations


The known close approach of Asteroid (99942) Apophis in April 2029 provides the opportunity for the case study of a potentially hazardous asteroid in advance of its encounter. The visible to near-infrared (0.55 to 2.45 μm) reflectance spectrum of Apophis is compared and modeled with respect to the spectral and mineralogical characteristics of likely meteorite analogs. Apophis is found to be an Sq-class asteroid that most closely resembles LL ordinary chondrite meteorites in terms of spectral characteristics and interpreted olivine and pyroxene abundances, although we cannot rule out some degree of partial melting. A meteorite analog allows some estimates and conjectures of Apophis' possible range of physical properties such as the grain density and micro-porosity of its constituent material. Composition and size similarities of Apophis with (25143) Itokawa suggest a total porosity of 40% as a "current best guess" for Apophis. Applying these parameters to Apophis yields a mass estimate of 2 × 1010 kg with a corresponding energy estimate of 375 Mt for its potential hazard. Substantial unknowns, most notably the total porosity, allow uncertainties in these mass and energy estimates to be as large as factors of two or three.

Original languageEnglish (US)
Pages (from-to)480-485
Number of pages6
Issue number2
StatePublished - Apr 2009
Externally publishedYes


  • Asteroids
  • Meteorites
  • Spectroscopy
  • composition

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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