NEO News (03/10/09) Update on DD45 & TN166

From Dave Morrison.

NEO News (03/10/09) Update on DD45 & TN166

2009DD45 SIZE MEASURED

As noted in NEO News of (03/07/09), the main press speculation about the close pass by NEA 2009DD45 concerned how much damage it would have caused had it hit the Earth. The range of diameters under consideration was from about 20m to 40m. These were estimates based only on the observed brightness. Rick Binzel and colleagues observed DD45 in the infrared from Mauna Kea and reported as follows to the Central Bureau for Astronomical Telegrams. R. P. Binzel, M. Birlan, and F. E. DeMeo, Paris Observatory, made 0.8- to 2.5-micron spectroscopic measurements on Mar. 2.6 UT using the NASA Infrared Telescope Facility 3-m reflector on Mauna Kea. Absorption bands revealed at 1 and 2 microns show the characteristics of the S-type class of asteroids. Using the average albedo value of 0.36 for small NEAs in this class and based on its observed brightness, the diameter is estimated to be 19 ± 4 m. This is near the lower size limit and, together with the stony composition, suggests that this object would likely have disintegrated too high to do any ground damage. Knowing the size also allows us to revise the estimate of how often a NEA of this size passes this close to Earth, to roughly once per year.

David Morrison

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2008TN166 -- NOT

We reported on 03/07 that asteroid 2008TN166 appeared to be the brightest (and presumably largest) new NEA discovered since 2001. Tim Spahr, the Director of the Minor Planet Center, reports that this was an MPC misidentification. Observations of three routine Main Belt Asteroids were incorrectly linked. There is no NEA and no orbit.

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