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When NASA scientists recently tracked the orbits of two space rocks as they neared Earth, they discovered a surprise: One of the asteroids has a small moon.
Astronomers regularly follow the trajectories of asteroids to ensure that none of them are on a potential collision course with our planet.
While none of the recent asteroids have moved within a worrisome distance, space rocks can provide valuable information that NASA uses to prepare for any possible future collision scenarios.
Asteroids, which are leftovers from the formation of the solar system, are also of interest because capturing details about their size, orbit and composition can reveal insights about our corner of the cosmos.
Astronomers at NASA’s Jet Propulsion Laboratory, located in Pasadena, California, used something called planetary radar through the Deep Space Network to track and take images of asteroids.
The Deep Space Network is a system of radio antennas on Earth that helps the agency communicate with spacecraft exploring our solar system and emits radio waves to act as radar in space.
The first space rock, asteroid 2011 UL21, passed Earth on June 27 at a distance of 4.1 million miles (6.6 million kilometers), or 17 times the distance between Earth and the Moon. Researchers first discovered the asteroid in 2011 using the Catalina Sky Survey in Tucson, Arizona. But since the space rock was first discovered, its June flyby of Earth has been the closest it has come to our planet that radar has imaged.
Astronomers beamed radio waves from the 230-foot (70-meter-wide) Goldstone Solar System Radar satellite dish near Barstow, California, to the space rock. The waves were reflected by the asteroid and returned to the satellite dish array antenna.
Researchers classified the nearly mile-wide (1.5 kilometer wide) asteroid as potentially hazardous, meaning it has a chance of impacting Earth in the future. But astronomers don’t think it will pose a threat to our planet for the foreseeable future, after calculating its future orbits and determining that it won’t come too close to Earth.
Radar images showed that the asteroid is roughly spherical and is one of a pair, called a binary system. The space rock has a small moon orbiting it from a distance of 1.9 miles (3 kilometers).
“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,” said Lance Benner, the principal scientist at JPL who led the observations, in a statement.
NASA missions, including the Lucy spacecraft that will explore a mysterious population of space rocks called Trojans later this decade, have helped discover how many moons exist around asteroids in our solar system.
And the DART mission intentionally crashed into a moon called Dimorphos, which orbits a larger asteroid called Didymos, to change the motion of a celestial body in space for the first time as a way to test the technology of asteroid deflection in 2022.
Sometimes, astronomers don’t know that an asteroid is in an orbit that keeps it close to Earth until just before its closest approach. That uncertainty it’s part of the reason NASA is ramping up efforts to better understand the population of asteroids that come closest to our world.
Researchers discovered asteroid 2024 MK just 13 days before it flew by Earth, passing just 184,000 miles (295,000 kilometers) from our planet — just over three-quarters of the distance between Earth and the Moon — on June 29.
The Asteroid Impact Warning System, or ATLAS, at the Sutherland Observatory in South Africa first detected the space rock on June 16. While also considered potentially dangerous, the asteroid doesn’t appear to be on a worrisome trajectory relative to Earth anytime soon.
Astronomers sent radio waves to the space rock and captured a detailed image of asteroid 2024 MK. Boulders 10 meters wide, as well as concave spots and ridges, litter its surface. The asteroid is 500 feet (150 meters) across and appears angular and elongated, while also having some noticeable flat and rounded areas.
As the space rock passed by our planet and encountered Earth’s gravity, its orbit changed. Now, the asteroid’s 3.3-year trip around the sun has been shortened by about 24 days.
Objects the size of asteroid 2024 MK come close to Earth only every two decades, so astronomers gathered as much data as they could.
“This was an incredible opportunity to investigate the physical properties and obtain detailed images of a near-Earth asteroid,” Benner said.