NASA’s Jet Propulsion Laboratory (JPL) in Southern California recently tracked two asteroids as they flew by Earth. The first asteroid, 2011 UL21, was discovered in 2011 by the NASA-funded Catalina Sky Survey and passed Earth on June 27 at a distance of 4.1 million miles (6.6 million kilometers). This was the first time it had come close enough to Earth to be imaged by radar. The asteroid, which is nearly a mile wide, is classified as potentially hazardous but poses no threat to our planet for the foreseeable future. Using the Deep Space Network’s 230-foot-wide Goldstone Solar System Radar, scientists discovered that 2011 UL21 is a binary system, with a smaller asteroid, or moonlet, orbiting it from a distance of about 1.9 miles (3 kilometers).
Two days later, on June 29, the same team observed the asteroid 2024 MK pass our planet from a distance of only 184,000 miles (295,000 kilometers). About 500 feet wide, this asteroid appears to be elongated and angular, with prominent flat and rounded regions. The scientists used the Goldstone Solar System Radar’s 114-foot DSS-13 antenna to receive the signal that bounced off the asteroid and came back to Earth. The result of this “bistatic” radar observation is a detailed image of the asteroid’s surface, revealing concavities, ridges, and boulders about 30 feet wide. Close approaches of near-Earth objects the size of 2024 MK are relatively rare, occurring about every couple of decades, on average.
The asteroid 2024 MK was first reported on June 16 by the NASA-funded Asteroid Terrestrial-impact Last Alert System (ATLAS) at Sutherland Observing Station in South Africa. Its orbit was changed by Earth’s gravity as it passed by, reducing 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 motion show that it does not pose a threat to our planet for the foreseeable future.
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. The Deep Space Network, which includes the Goldstone Solar System Radar, receives programmatic oversight from Space Communications and Navigation program office within the Space Operations Mission Directorate, also at NASA Headquarters. These radar observations provide valuable practice for planetary defense and offer information about the sizes, orbits, rotation, surface details, composition, and formation of near-Earth objects.
