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Spectral properties and composition of potentially hazardous Asteroid (99942) Apophis |
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| Authors: | 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 |
| Affiliation: | aDepartment of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology, Building 54, Room 410, 77 Massachusetts Avenue, Cambridge, MA 02139, USA;bAssociate Researcher, IMCCE-Observatoire de Paris, 77 Avenue Denfert-Rochereau, Paris 75014, France;cJohns Hopkins University Applied Physics Laboratory, 11100 Johns Hopkins Road, Laurel, MD 20723, USA;dResearch and Scientific Support Department, European Space Agency, Keplerlaan 1, 2201 AZ Noordwijk, The Netherlands;eDepartments of Geology & Physics and Astronomy, Bates College, Lewiston, ME 04240, USA;fLaboratoire d'Etudes Spatiales et d'Instrumentation en Astrophysique, Observatoire de Paris, F-92195 Meudon Principal Cedex, France;gInstitute for Astronomy, University of Hawaii, 640 North A'ohoku Place, Hilo, HI 96720, USA;hInstitute for Astronomy, University of Hawaii, 2680 Woodlawn Dr., Honolulu, HI 96822, USA;iInstitut de Mecanique Celeste et de Calcul des Ephemerides, Observatoire de Paris, 77 Avenue Denfert-Rochereau, Paris 75014, France;jAssociate Researcher, Astronomical Institute of the Romanian Academy, Cutitul de Argint-5, 040557, Bucharest, Romania |
| Abstract: | 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. |
| Keywords: | Asteroids, composition Spectroscopy Meteorites |
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