The two asteroids – 2024 MK and 2011 UL21 – were recently tracked by scientists at NASA's Jet Propulsion Laboratory in Southern California, a statement said.
It said one of them had a small moon orbiting it, while the other was discovered just 13 days before its closest approach to Earth. It also said that “none of the near-Earth objects pose any risk of colliding with our planet.”
Asteroid 2011 UL21
On June 27, this asteroid passed 4.1 million miles (or 6.6 million kilometers) from Earth. This is about 17 times the distance between the Moon and Earth. As the name suggests, this asteroid was discovered in 2011 by the Catalina Sky Survey in Tucson, Arizona.
However, this was the first time it came so close to Earth that it could be imaged by radar. Although the approximately 1.5 kilometer wide object has been classified as potentially hazardous, calculations of its future orbit suggest that it will not pose any threat to Earth in the near future.
Using the 230-foot-wide (70-meter) Goldstone Solar System Radar — called Deep Space Station 14 (DSS-14) — scientists transmitted radio waves to the asteroid and later received the reflected signals through the same antenna. In addition to determining that it is roughly spherical, they also discovered that it is a binary system, meaning that a smaller asteroid, or moon, orbits it at a distance of about three kilometers.
Asteroid 2024 MK
On June 29, two days after 2011 UL21, the same team of scientists observed asteroid 2024 MK pass just 295,000 kilometers from Earth. This is a little more than three-quarters of the distance between the Moon and Earth.
The asteroid is about 500 feet (or 150 meters) wide and appears elongated and angular, with prominent flat and rounded regions.
To see it, they used DSS-14 to send radio waves to the object. But this time, they used Goldstone's 114-foot (34-meter) DSS-13 antenna to receive the signal as it hit the asteroid.
“The result of this 'bistatic' radar observation is a detailed image of the asteroid's surface, showing concavities, ridges and boulders about 30 feet (10 meters) wide,” NASA said.
The space agency said close approaches of near-Earth objects the size of 2024 MK are “relatively rare” and typically occur about every two decades.
The 2024 MK was first reported on June 16.