OSIRIS-REx Scientists Measure Yarkovsky Effect
The new orbit for the half-kilometer (one-third mile) diameter 1999 RQ36 is the most precise asteroid orbit ever obtained, OSIRIS-REx team member Steven Chesley of the NASA Jet Propulsion Laboratory said. He presented the findings May 19 at the Asteroids, Comets and Meteors 2012 meeting in Niigata, Japan.
Remarkable observations that Michael Nolan at Arecibo Observatory in Puerto Rico made in September, along with Arecibo and Goldstone radar observations made in 1999 and 2005, when 1999 RQ36 passed much closer to Earth, show that the asteroid has deviated from its gravity-ruled orbit by roughly 100 miles, or 160 kilometers, in the last 12 years, a deviation caused by 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 difficult to measure because it's so infinitesimally small, Chesley said.
"The Yarkovsky force on 1999 RQ36 at its peak, when the asteroid is nearest the sun, is only about a half-ounce -- about the weight of three grapes on Earth. Meanwhile, the mass of the asteroid is estimated to be about 68 million tons. You need extremely precise measurements over a fairly long time span to see something so slight acting on something so huge."
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