Paris Astronomers "Catch" Passing Asteroid
Publiée le 2009-03-09
The small asteroid 2009 DD45 which whizzed past Earth on Monday was "caught" by a team of astronomers working at the Paris Observatory. This close encounter asteroid was discovered on 27 February 2009, by Rob McNaught at Siding Spring Observatory, Australia. On 2 March 2009, at 15h Paris Local Time, the asteroid was passing at its closest distance from the Earth, about 0.00048 AU (approximately 64,000 km). For a short period of time of about two hours, the brightness of the object allowed spectroscopic observations.

How could a Paris Observatory team measure this asteroid, which passed the opposite side of the Earth, soaring over Tahiti? A special facility of the Observatory, the Centre d'Observation à Distance en Astronomie à Meudon (CODAM) allowed the Paris team to command the 3 metre diameter telescope IRTF, a highly specialized telescope located at Mauna Kea, Hawaii. From Meudon, the Paris team was able to use the Hawaii telescope to track down the space intruder and capture its light into the telescope's near-infrared spectrograph, SpeX.

The resulting spectral colors, measured over the infrared wavelengths 0.8-2.5 micron, revealed characteristic signatures of the minerals olivine and pyroxene (commonly found in both meteorites and Earth rocks), placing the asteroid into a category that astronomers refer to as the S-class. By knowing this class, the team can associate 2009 DD45 with other small S-class asteroids which have measured values for their reflectivity; about 36% of the sunlight hitting the asteroid is reflected (results from Delbo et al. 2003, Icarus 166, 116).From the brightness of the asteroid, and its reflectivity, the Paris team could deduce the mean diameter to be 19 +/- 4 meters.

Contact persons:

Richard Binzel (Massachusetts Institute of Technology, invited researcher LESIA, IMCCE, Observatoire de Paris)

Francesca DeMeo (LESIA, Observatoire de Paris)

Mirel Birlan (IMCCE, Observatoire de Paris)

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