The Deep Space Network’s Goldstone Planetary Radar has been busy tracking asteroids 2024 MK and 2011 UL21 for several days as they safely pass by Earth. Researchers at NASA’s Jet Propulsion Laboratory (JPL) in Southern California recently tracked two asteroids that passed by our planet. One has a small moon orbiting it, while the other was discovered just 13 days before its closest approach to Earth.

Although there is no risk of any near-Earth object hitting our planet, radar observations during these two close approaches will provide valuable practices for protecting the planet, as well as information about the planet’s size, orbit, rotation, surface details, and clues about its composition and formation.

Articles from the collision with asteroid UL21 in 2011

After passing Earth on June 27 at a distance of 4.1 million miles (6.6 million kilometers), about 17 times the distance between the Moon and Earth, asteroid 2011 UL21 was discovered in 2011 by the NASA-funded Catalina Sky Survey in Tucson, Arizona. But this was the first time it had come close enough to Earth to be detected by radar. Although the object, which is about 1 mile wide (1.5 kilometers), is classified as potentially hazardous, calculations of its future orbit suggest that it will not pose a threat to our planet in the foreseeable future.

Using the Goldstone Solar System Deep Space Network’s 230-foot-wide (70-meter) radar, called Deep Space Station 14 (DSS-14), near Barstow, California, JPL scientists beamed radio waves at the asteroid and received signals reflected off the asteroid using the same antenna. In addition to identifying a roughly spherical asteroid, they discovered that it was a binary system containing a smaller asteroid or moon orbiting it at a distance of about 1.9 miles (3 kilometers).

“Roughly two-thirds of asteroids this size are thought to be binary systems, and their discovery is particularly important because we can use measurements of their relative positions to estimate their relative orbits, masses and densities, providing important insights into how they might have formed,” said Lance Banner, JPL’s principal scientist who led the observations.

Second close approach

Two days later, on June 29, the same team watched asteroid 2024 MK pass by our planet from a distance of just 184,000 miles (295,000 kilometers), a little more than three-quarters of the distance between the Moon and Earth. About 500 feet (150 meters) across, the asteroid looks long and strange, with distinct flat and rounded areas.

For these observations, the scientists also used DSS-14 to transmit radio waves to the object, but they used Goldstone’s 34-foot (114-meter) DSS-13 antenna to receive the signal reflected off the asteroid and returned to Earth. The result of this “bistatic” radar observation is a detailed image of the asteroid’s surface, revealing depressions, protrusions, and rocks about 30 feet (10 meters) wide.

Close approaches of near-Earth objects the size of 2024 MK are relatively rare—on average, every few decades—so the JPL team sought to collect as much data about the object as possible. “This was an extraordinary opportunity to investigate the physical properties of a near-Earth asteroid and obtain detailed images of it,” Benner said.

Contribution to planetary protection

Asteroid 2024 MK was first reported by the NASA-funded Asteroid Late Earth Alert System (ATLAS) at the Sutherland Observatory in South Africa on June 16. Its orbit was altered by Earth’s gravity as it passed, shortening its 3.3-year orbital period around the Sun by about 24 days. Although it is classified as a potentially hazardous asteroid, calculations of its future movement suggest that it does not pose a threat to our planet in the foreseeable future.

The Goldstone Solar System Radar Group is supported by NASA’s Near-Earth Object Observations Program within the agency’s Planetary Defense Coordination Office at headquarters in Washington. The Deep Space Network, managed by JPL, receives programmatic oversight from the Space Communications and Navigation Program Office in the Space Operations Executive, also located at NASA Headquarters.