July 31, 2015

Peanut-Shape Asteroid Imaged with Radar During Earth Flyby

A team of scientists has used two giant radio telescopes to bounce radar signals off a passing asteroid and produce images of its peanut-shape body as it approached close to Earth this past weekend.

The asteroid appears to be a contact binary -- an asteroid with two lobes that are stuck together.

The images show the rotation of the asteroid, named 1999 JD6, which made its closest approach on July 24 at 9:55 p.m. PDT (12:55 a.m. EDT on July 25) at a distance of about 7.2 million kilometers, or about 19 times the distance from Earth to the Moon.

"Radar imaging has shown that about 15 percent of near-Earth asteroids larger than 600 feet [about 180 meters], including 1999 JD6, have this sort of lobed, peanut shape," said Lance Benner of NASA's Jet Propulsion Laboratory in Pasadena, California, who leads NASA's asteroid radar research program.

To obtain the views, researchers paired NASA's 70 meter Deep Space Network antenna at Goldstone, California, with the National Science Foundation’s 100 meter Green Bank Telescope (GBT) in West Virginia. Using this approach, the Goldstone antenna beams a radar signal at an asteroid and the GBT receives the reflections. The technique, referred to as a bistatic observation, dramatically improves the amount of detail that can be seen in radar images. The new views obtained with the technique show features as small as about 7.5 meters wide.

The individual images used in the movie were generated from data collected on July 25. They show the asteroid is highly elongated, with a length of approximately 2 kilometers on its long axis. The movie spans a period of about seven hours, 40 minutes.

This week's flyby was the closest approach the asteroid will make to Earth for about the next 40 years. The next time it will approach Earth this closely is in 2054, at approximately the same distance of this week's flyby.

Data from the new observations will be particularly useful to Sean Marshall, a graduate student at Cornell University in Ithaca, New York, whose doctoral research on 1999 JD6 is funded by NASA's Near-Earth Object Program. "I'm interested in this particular asteroid because estimates of its size from previous observations, at infrared wavelengths, have not agreed. The radar data will allow us to conclusively resolve the mystery of its size to better understand this interesting little world," he said.

Despite the uncertainty about its size, asteroid 1999 JD6 has been studied extensively and many of its physical properties, as well as its trajectory, are well known. It rotates in just over seven-and-a-half hours and is thought to be a relatively dark object. Asteroid 1999 JD6 was discovered on May 12, 1999, by the Lowell Observatory Near-Earth-Object Search, located in Flagstaff, Arizona.

Radar is a powerful technique for studying an asteroid's size, shape, rotation state, surface features and surface roughness, and for improving the calculation of asteroid orbits. Radar measurements of asteroid distances and velocities often enable computation of asteroid orbits much further into the future than would be possible otherwise.

The 100-meter Green Bank Telescope is the world's largest fully steerable radio telescope. Its location in the National Radio Quiet Zone and the West Virginia Radio Astronomy Zone protects the incredibly sensitive telescope from unwanted radio interference, enabling it to perform unique observations.

The National Radio Astronomy Observatory is a facility of the National Science Foundation, operated under cooperative agreement by Associated Universities, Inc.

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Contact: Charles Blue
NRAO Public Information Officer
(434) 296-0314; cblue@nrao.edu

PIA19647This collage of radar images of near-Earth asteroid 1999 JD6 shows the rotation of the asteroid, which made its closest approach on July 24 at 9:55 p.m. PDT (12:55 a.m. EDT on July 25) at a distance of about 4.5 million miles (7.2 million kilometers, or about 19 times the distance from Earth to the Moon). Credit: NASA/JPL-Caltech/GSSR; NRAO/AUI/NSF
This video was created from of radar images of near-Earth asteroid 1999 JD6 taked on July 25, 2015. The asteroid appears to be a contact binary -- an asteroid with two lobes that are stuck together. The radar images, taken by pairing NASA's Deep Space network antenna at Goldstone, California, with the NSF's Green Bank Telescope in Green Bank, West Virginia, show the asteroid is highly elongated, with a length of approximately 1.2 miles (2 kilometers) on its long axis. Credit: NASA/JPL-Caltech; NRAO/AUI/NSF