Radar image of asteroid 1998 QE2 and its moon taken on June 7, 2013, by the Arecibo Observatory. Several craters are visible on the asteroid, and the moon appears as a bright streak. Each pixel is 7.5 meters (25 feet). (Arecibo Observatory/NASA/Ellen Howell)
An unprecedented look at an asteroid that sailed past Earth last week came with a surprise: the space rock had its own moon.
By bouncing radio waves off the asteroid, researchers were not only able to map the rock's surface, but determine how fast the "moonlet" was orbiting. Because the moon is approximately proportional in size to QE2 as our moon is to Earth, the researchers are able to calculate the mass of the asteroid.
Spectrum data out of NASA's Infrared Telescope Facility in Hawaii revealed QE2 is a "primitive" asteroid, meaning its surface has not been significantly altered from its original composition, and could provide new insight into the origin of the solar system.
"Asteroid QE2 is dark, red, and primitive -- that is, it hasn’t been heated or melted as much as other asteroids," Arecibo's Ellen Howell said in a statement. "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," Howell said.
The Arecibo Telescope, the largest single-dish telescope in the world at 300 meters wide, works just like radar guns used for law enforcement or pitch speed in baseball. It bounces radio waves off a moving object and then determines the speed and shape of the object based on the reflection of the waves it gets back.