New information on Apophis Composition (from MIT)

From the article:

By analysing its spectrum and comparing it with meteorites that have already landed on Earth, the team has "nailed" its composition, says Richard Binzel, professor of planetary sciences in MIT's Department of Earth, Atmospheric, and Planetary Sciences (EAPS)...Their work suggests that Apophis is a rare type, known as LL chondrite. Just seven per cent of the space rocks that land on Earth are a match to this pyroxene and olivine-rich rock, the team says.

Information from abstract:

Spectral Properties and Composition of Potentially Hazardous Asteroid (99942) Apophis
Richard P. Binzel1, A. S. Rivkin2, C. A. Thomas1, P. Vernazza3, T. H. Burbine4, F. E. DeMeo1, S. J. Bus5, A. T. Tokunaga5, M. Birlan6
1MIT, 2JHU APL, 3LESIA - Obs. Paris, France, 4Mt. Holyoke College, 5Institute for Astronomy, Univ. Hawaii, 6IMCCE, Observatoire de Paris, France.

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 (0.5- to 2.5-micron) reflectance spectrum of Apophis, obtained with the Magellan and NASA IRTF telescopes, 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 its spectral characteristics and in terms of its interpreted olivine and pyroxene abundances. The value of a meteorite association is that it allows physical constraints to be placed on the nature of Apophis. For example, an ordinary chondrite analog allows inference of Apophis' physical properties such as the grain density and micro-porosity of its constituent material. We note that an LL-chondrite interpretation for Apophis is similar to that for (25143) Itokawa, for which in situ spacecraft measurements are available. If we may use Itokawa as an analogy, this suggests for Apophis a total porosity of 40% as a "best guess." Using these "best guess" parameters yields a mass estimate of 2 x 10^10 kg and a kinetic energy estimate of 375 Mt for its potential hazard. Actual unknowns, most notably in the total porosity, allow uncertainties in these mass and energy estimates to be as large as a factor of two or three.

Link: Abstract from Oct. 9 meeting of the Division for Planetary Sciences of the American Astronomical Society Annual Meeting

Link: MIT Article

Link: Article (Register)