Asteroid 1998 QE2 turns while its moon zips upward. Credit: Ellen Howell / NASA / Arecibo





The Arecibo Observatory in Puerto Rico has captured the most detailed radar images yet of asteroid 1998 QE2 and its newly discovered moon.

A sequence of pictures released on Friday shows the 1.9-mile-wide (3-kilometer-wide) asteroid rotating in outer space while its 2,500-foot-long (750-meter-long companion zips around it. The asteroid and its moon sped past Earth harmlessly at a minimum distance of 3.6 million miles (5.8 million kilometers) on May 31.

"Asteroid QE2 has no chance of hitting Earth," Michael Nolan, head of the 1,000-foot-wide (300-meter-wide) telescope's asteroid radar group, said in a statement from the Universities Space Research Association, or USRA.

The Arecibo Observatory, sponsored by the National Science Foundation, is the world's largest and most sensitive single-dish radio telescope. Astronomers have been using Arecibo and NASA's Goldstone radar installation in California to track the movements of 1998 QE2 and its moon after its close encounter. Radar readings have revealed craters on the surface of the large rock.

Scientists estimate that one-sixth of all near-Earth asteroids have moons. "QE2's moon is roughly one-quarter the size of the main asteroid," said Patrick Taylor a USRA research astronomer at Arecibo. "Similarly, our moon is also approximately one-fourth the size of our planet."

Analyzing the motion of QE2's moon will help scientists determine the mass of the main asteroid.

"Being able to determine its mass from the moon helps us understand better the asteroid's material," said Ellen Howell, a USRA research astronomer who captured radar images of the asteroid at Arecibo and optical and infrared images using the Infrared Telescope Facility in Hawaii. The optical images can provide spectral data, revealing what the asteroid is made of.

"What makes this asteroid so interesting, aside from being an excellent target for radar imaging, is the color and small moon," Howell said in the USRA statement. "Asteroid QE2 is dark, red, and primitive — that is, it hasn't been heated or melted as much as other asteroids. QE2 is nothing like any asteroid we've visited with a spacecraft, or plan to, or that we have meteorites from. It's an entirely new beast in the menagerie of asteroids near Earth."

1998 QE2 gets its name from the timing of its discovery. The "QE2" refers to the order in which the asteroid was found during the latter half of August 1998. For what it's worth, 1998 QE2's diameter is nine times the length of the ocean liner Queen Elizabeth 2.

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USRA's Michael Nolan led the radar observations of QE2, along with Ellen Howell, Patrick Taylor, Alessondra Springmann, Sean Marshall of Cornell University, and Mariah Law of Embry-Riddle Aeronautical University, in collaboration with the Near-Earth Object radar team at NASA's Jet Propulsion Laboratory and Goldstone Observatory in California. Observations continued through Thursday morning.

Alan Boyle is NBCNews.com's science editor. Connect with the Cosmic Log community by "liking" the NBC News Science Facebook page, following @b0yle on Twitter and adding the Cosmic Log page to your Google+ presence. To keep up with NBCNews.com's stories about science and space, sign up for the Tech & Science newsletter, delivered to your email in-box every weekday. You can also check out "The Case for Pluto," my book about the controversial dwarf planet and the search for new worlds.