NASA's planetary radar tracks the approach of two large asteroids to Earth

According to NASA, this mosaic shows the spinning asteroid in one-minute increments about 16 hours after its closest approach. Asteroid 2024 MK.

Scientists at NASA's Jet Propulsion Laboratory in Southern California recently tracked two asteroids passing by our planet. One of them had a small moon orbiting around it, while the other had been discovered just 13 days before its closest approach to Earth. There was no risk of either of the two nearby objects impacting our planet, but radar observations taken during these two close approaches will provide valuable practice for planetary defence, as well as information about their sizes, orbits, rotation, surface details. and clues about its composition and formation.

The two asteroids that passed close to Earth in June 2024: 2011 UL21 and 2024 MK

Asteroid 2011 UL21

It passed close to Earth on June 27 at a distance of 6.6 million kilometres (about 17 times the distance between the Moon and Earth), and was discovered in 2011 by the NASA-funded Catalina Sky Survey in Tucson, Arizona. But this is the first time it has come close enough to Earth to be imaged by radar. While the nearly 1.5 kilometre wide object is classified as potentially dangerous, calculations of its future orbits show that it will not pose a threat to our planet in the foreseeable future.

Using the Deep Space Network's 70-metre-wide Goldstone Solar System radar, called Deep Space Station 14 (DSS-14), near Barstow, California, JPL scientists transmitted radio waves to the asteroid and received the reflected signals. by the same antenna. In addition to determining that the asteroid is approximately spherical, they discovered that it is a binary system: a smaller asteroid, or moon, orbits it at a distance of about 3 kilometres.

“About two-thirds of asteroids of 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 mutual orbits, masses and densities, which provide key information about how they may have formed.” formed,” said Lance Benner, a senior scientist at JPL who helped lead the observations.

Second close arrival: the 2024 MK

Two days later, on June 29, the same team observed asteroid 2024 MK pass by our planet at a distance of just 295,000 kilometres, or a little more than three-quarters of the distance between the Moon and Earth. This about 150 metre wide asteroid appears to be elongated and angular, with prominent flat and rounded regions. For these observations, scientists also used DSS-14 to transmit radio waves to the object, but used Goldstone's 34-metre DSS-13 antenna to receive the signal that bounced off the asteroid and returned to Earth. The result of this "bistatic" radar observation is a detailed image of the asteroid's surface, revealing concavities, ridges and rocks about 10 metres (30 feet) wide.

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

Asteroid 2024 MK was first detected on June 16, 2024 by the NASA-funded Asteroid Terrestrial Impact Last Alert System (ATLAS) at the Sutherland Observing Station in South Africa. Its orbit was modified by Earth's gravity in its path, reducing its 3.3-year orbital period around the Sun by about 24 days. Although it is classified as a potentially dangerous asteroid, calculations of its future movement show 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 Planetary Defence Coordination Office at the agency's headquarters in Washington.