Fri05 NASA Scientist Figures Way to Weigh Space Rock

A scientist at NASA's Jet Propulsion Laboratory in Pasadena, Calif., has accurately determined the mass of a nearby asteroid from millions of miles away. The celestial equivalent of "guess your weight" was achieved by Steve Chesley of JPL's Near-Earth Object Program Office by utilizing data from three NASA assets - the Goldstone Solar System Radar in the California desert, the orbiting Spitzer Space telescope, and the NASA-sponsored Arecibo Observatory in Puerto Rico. 

Chesley presented his findings this past Saturday, May 19, at the Asteroids, Comets and Meteors 2012 meeting in Niigata, Japan. 

For Chesley to define the asteroid's mass, he first needed to understand its orbit and everything that could affect that orbit -- including neighboring celestial bodies and any propulsive force (however minute) the asteroid could generate.

Incorporating extraordinarily precise observations collected by astronomer Michael Nolan at Arecibo Observatory in September 2011, Arecibo and Goldstone radar observations made in 1999 and 2005, and the gravitational effects of the sun, moon, planets and other asteroids, Chesley was able to calculate how far the asteroid deviated from its anticipated orbit. He found that 1999 RQ36 had deviated from the mathematical model by about 100 miles (160 kilometers)in the past 12 years.  The only logical explanation for this orbital change was that the space rock itself was generating a minute propulsive force known in space rock circles as the Yarkovsky effect.

The Yarkovsky effect is named for the 19th-century Russian engineer who first proposed the idea that a small, rocky space object would, over long periods of time, be noticeably nudged in its orbit by the slight push created when it absorbs sunlight and then re-emits that energy as heat. The effect is hard to measure because it's so infinitesimally small. 

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