NASA radar reveals passing asteroid has its own moon

Scientists have discovered that the asteroid 1998 QE2, which makes it closest approach to Earth on May 31, is actually a binary system.
By | Published: May 31, 2013 | Last updated on May 18, 2023
Asteroid 1998 QE2 binary
First radar images of asteroid 1998 QE2 were obtained when the asteroid was about 3.75 million miles (6 million kilometers) from Earth. The small white dot at lower right is the moon, or satellite, orbiting the asteroid. // NASA/JPL-Caltech/GSSR
A sequence of radar images of asteroid 1998 QE2 was obtained on the evening of May 29, 2013, by NASA scientists using the 230-foot (70 meters) Deep Space Network antenna at Goldstone, California, when the asteroid was about 3.75 million miles (6 million kilometers) from Earth, which is 15.6 lunar distances.

Watch the flyby of asteroid 1998 QE2 starting at 4:30 p.m. EDT at

The radar imagery revealed that 1998 QE2 is a binary asteroid. In the near-Earth population, about 16 percent of asteroids that are about 655 feet (200m) or larger are binary or triple systems. Radar images suggest that the main body, or primary, is approximately 1.7 miles (2.7 kilometers) in diameter and has a rotation period of less than four hours. Also revealed in the radar imagery of 1998 QE2 are several dark surface features that suggest large concavities. The preliminary estimate for the size of the asteroid’s satellite, or moon, is approximately 2,000 feet (600m) wide. The radar collage covers a little bit more than two hours.

The radar observations were led by scientist Marina Brozovic of NASA’s Jet Propulsion Laboratory, Pasadena, California.

The closest approach of the asteroid occurs today at 20h59m UT (4:59 p.m. EDT), when the asteroid will get no closer than about 3.6 million miles (5.8 million km), or about 15 times the distance between Earth and the Moon. This is the closest approach the asteroid will make to Earth for at least the next two centuries. Asteroid 1998 QE2 was discovered August 19, 1998, by the Massachusetts Institute of Technology Lincoln Near Earth Asteroid Research (LINEAR) program near Socorro, New Mexico.

The resolution of these initial images of 1998 QE2 is approximately 250 feet (75m) per pixel. Resolution is expected to increase in the coming days as more data become available. Between May 30 and June 9, radar astronomers using the Deep Space Network antenna and the Arecibo Observatory in Puerto Rico will perform an extensive campaign of observations on asteroid 1998 QE2. The two telescopes have complementary imaging capabilities that will enable astronomers to learn as much as possible about the asteroid during its brief visit near Earth.

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 if radar observations weren’t available.