Asteroid Spin May Reveal Clues About Its Future Orbital Path
February 12, 2013

Asteroid Spin May Reveal Clues About Its Future Orbital Path

April Flowers for - Your Universe Online

On February 15, astronomers will have an exciting opportunity with a record-setting close approach of an asteroid.  The research team, using the National Radio Astronomy Observatory (NRAO) and NASA telescopes, will gain a key clue that will help predict the future of this natural cosmic orbiter.

Discovered just a year ago, the 150-foot-wide asteroid, called 2012 DA14, will pass only 17,200 miles from the Earth on Friday, which is closer than the geosynchronous communication and weather satellites in Earth's orbit. The asteroid will definitely not collide with the Earth; however, this is a record close approach for an object of this size. Astronomers around the world are preparing for the exciting chance to study this asteroid up close and personal.

NRAO astronomer Michael Busch and colleagues will use a novel observational technique to determine which way the space rock is spinning as it speeds on its orbit through the Solar System.  Direction of spin is an important factor in predicting how the object's orbit might change over time.

"Knowing the direction of spin is essential to accurately predicting its future path, and thus determining just how close it will get to Earth in the coming years," Busch said in a statement.

The team plans to use the the Karl G. Jansky Very Large Array (VLA) and the Very Long Baseline Array (VLBA) antennas at Pie Town and Los Alamos, New Mexico, respectively.  Additionally, they will use the Solar System radar on NASA's 230-foot antenna at Goldstone, California, to transmit a powerful beam of radio waves toward the asteroid.  The NRAO telescopes will receive the waves reflected from the asteroid's surface.

The reflected radar signal will have a characteristic signature, or "speckles," as observed from Earth. This is because of the asteroid's uneven surface and the different reflectivity of portions of the surface.  The astronomers can learn which way the asteroid is spinning by measuring which antenna in a widely separated pair receives the speckle pattern first.  The research team has developed special techniques for processing the data as this method of using the telescopes is significantly different than their normal astronomical use.

What does this information teach us about the asteroid's orbital changes?  The asteroid develops a warm region that radiates infrared light in its maximum amount during "afternoon" on the asteroid, much like afternoon on Earth is the warmest part of the day. This radiation provides a gentle but firm jet-like push to the asteroid. Whether the "afternoon" is forward or rearward of its direction of motion is determined by the asteroid's spin direction.

In turn, this positioning determines the speed of spin.  If the infrared hot spot is forward of the direction of spin, the asteroid's orbital speed will slow down.  However, if the hot spot is rearward of the motion, the speed of the orbital motion will speed up.  Over time, this effect — called the Yarkovsky Effect after the engineer who identified it -  can make a significant difference in orbit.

"When the asteroid passes close to the Earth or another large body, its orbit can be changed quickly by the gravitational effect of the larger body, but the Yarkovsky Effect, though smaller, is at work all the time," Busch said.

The team will make their observations using the Goldstone-VLA-VLBA on Feb 16, when the asteroid's South-to-North motion makes it readily visible to those antennas.