Goldstone Planetary Radar Observes Binary Asteroid 2011 UL21

This series of seven radar observations by the Deep Space Network's Goldstone Solar System Radar shows the asteroid 2011 UL21 during its close approach with Earth from 4.1 million miles (6.6 million kilometers) away – about 17 times the distance between the Moon and Earth. White circles highlight the main asteroid and its small moon (a bright dot at the bottom of the image).

Passing Earth on June 27, 2024, the asteroid was discovered in 2011 by the NASA-funded Catalina Sky Survey, in Tucson, Arizona. This marked the first time it came close enough to Earth to be imaged by radar. While the nearly mile-wide (1.5-kilometer-wide) object is classified as being potentially hazardous, calculations of its future orbits show that it won't pose a threat to our planet for the foreseeable future.

In addition to determining the asteroid is roughly spherical, scientists at NASA's Jet Propulsion Laboratory discovered that it's a binary system: A smaller asteroid, or moonlet, orbits it from a distance of about 1.9 miles (3 kilometers).

The Goldstone Solar System Radar Group is supported by NASA's Near-Earth Object Observations Program within the Planetary Defense Coordination Office at the agency's headquarters in Washington. Managed by NASA's Jet Propulsion Laboratory, the Deep Space Network receives programmatic oversight from Space Communications and Navigation program office within the Space Operations Mission Directorate, also at NASA Headquarters.

More information about planetary radar and near-Earth objects can be found at: https://www.jpl.nasa.gov/asteroid-watch