1998 QE2: more info

With additional radar images and time for analysis, NASA scientists have been able to refine their estimates of the asteroid's size and rotation. The data indicate the main, or primary body, is approximately 1.9 miles (3 kilometers) in diameter and has a rotation period of about five hours.

The asteroid's satellite, or moon, is approximately 2,000 feet (600 meters) wide, has an elongated appearance, and completes a revolution around its host body about once every 32 hours. At any point during its orbit, the maximum distance between the primary body and moon is about 4 miles (6.4 kilometers). Similar to our moon, which always points the same "face" at Earth, the asteroid's satellite appears to always show the same portion of its surface to the primary asteroid. This is called "synchronous rotation."

1998 QE2 is one of the slowest (with respect to its rotation) and largest binaries that have been observed by planetary radar. In the near-Earth population, about 16 percent of asteroids that are about 655 feet (200 meters) or larger are binary or triple systems.

The trajectory of asteroid 1998 QE2 is well understood. The closest approach of the asteroid occurred on May 31 at 1:59 p.m. PDT (4:59 p.m. EDT / 20:59 UTC), when the asteroid got no closer than about 3.6 million miles (5.8 million kilometers), or about 15 times the distance between Earth and the moon. This was the closest approach the asteroid will make to Earth for at least the next two centuries.

Asteroid 1998 QE2 was discovered on Aug. 19, 1998, by the Massachusetts Institute of Technology Lincoln Near Earth Asteroid Research (LINEAR) program near Socorro, N.M.

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.

NASA places a high priority on tracking asteroids and protecting our home planet from them. In fact, the US has the most robust and productive survey and detection program for discovering near-Earth objects (NEOs). To date, U.S. assets have discovered over 98 percent of the known NEOs.

In addition to the resources NASA puts into understanding asteroids, it also partners with other U.S. government agencies, university-based astronomers, and space science institutes across the country that are working to track and better understand these objects, often with grants, interagency transfers and other contracts from NASA.