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Another Reason to Worry about NEOs

June 8, 2012; 5:22 AM ET

A team of NASA scientists have measured the weight and orbit of 1999 RQ36. They have found the asteroid has a low density and its orbit has drifted roughly 100 miles in the last 12 years. This deviation is caused by the Yarkovsky effect. This effect can either push an asteroid into the Earth's orbit.... or away.

This puts an interesting twist on NEOs (Near Earth Objects) that I recently blogged about here.

This team's work using NASA's Spitzer Space Telescope in 2007 was crucial in determining the effect. They measured the asteroid's thermal characteristics using infrared emissions and determined the space rock was covered in an insulating blanket of fine material -- a key factor for the effect.

The Yarkovsky effect sharpens the picture of how potentially hazardous 1999 RQ36 could be in the future. The 1,640-foot-diameter asteroid is expected to pass by Earth in 2135 at around 220,000 miles. At such close distances, the asteroid's subsequent trajectory becomes impossible to predict accurately so close approaches can only be studied statistically. Imagine if this effect pushes it closer to the Earth or even causes it to be on a collision course with the Earth!

Due to this discovery, scientists now have identified many low-probability potential impacts in the 2170s through the 2190s while ruling out others.

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 when it absorbs sunlight and then re-emits that energy as heat. The effect is difficult to measure because it's so infinitesimally small.

The effect was discovered on 1999 RQ36 in an effort to determine the mass of the asteroid from millions of miles away. The scientists needed the space rock's size, thermal properties, propulsive force (Yarkovsky effect) and orbit to calculate the bulk density.

This radar image of asteroid 1999 RQ36 was obtained NASA's Deep Space Network antenna in Goldstone, Calif., on Sept. 23, 1999.

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Astronomy Blog
The AccuWeather.com astronomy blog, by Mark Paquette, discusses stargazing and astronomy issues and how the weather will interact with current astronomy events.