NASA/JPL-Caltech
NASA’s Goldstone Solar System Radar recently observed asteroid 2024 MK, which made its closest approach to Earth on June 29.
Subscribe to CNN’s Wonder Theory science newsletter. Explore the universe with news about fascinating discoveries, scientific advances and more.
CNN
—
When NASA scientists recently tracked the orbits of two space rocks as they closely approached Earth, they discovered a surprise: One of the asteroids has a small moon.
Astronomers regularly track the trajectories of asteroids to make sure none of them are on a potential collision course with our planet.
While none of the recent asteroids have whizzed by within offensive distance, space rocks can provide valuable information that NASA uses to prepare for 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 into 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 pictures 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, emitting radio waves that act like radar across 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), 17 times the distance between Earth and the Moon. Scientists first discovered the asteroid in 2011 using the Catalina Sky Survey in Tucson, Arizona. Since the space rock was first spotted, its flyby of Earth in June was the closest our planet has swerved on radar.
Astronomers beamed radio waves from the 230-foot-wide (70-meter-wide) Goldstone Solar System Radar satellite dish near Barstow, California, into the space rock. The waves bounced off the asteroid and traveled back to the network satellite antenna.
Researchers have labeled the nearly mile-wide (1.5 kilometer) asteroid potentially hazardous, meaning it has a chance of hitting Earth in the future. But astronomers don’t think it will pose a threat to our planet in the foreseeable future after calculating its future orbits and determining that it won’t come too close to Earth.
Radar images have shown that the asteroid is roughly spherical and is one of a pair called a binary system. The Space Stone has a small moon orbiting it from a distance of 3 km.
NASA/JPL-Caltech
Seven radar observations show the mile-wide asteroid 2011 UL21 during its close approach to Earth on June 27 from a distance of about 4 million miles. The asteroid and its small moon are circled in white.
“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 relative orbits, masses and densities, providing key information about how they may have formed, Lance Benner, JPL’s principal scientist who led the observations, said in a statement.
NASA missions, including the Lucy spacecraft, which will explore a mysterious space rock population called Trojans later this decade, have helped reveal 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 asteroid deflection technology in 2022.
Sometimes astronomers don’t know an asteroid is in an orbit that carries it close to Earth until it approaches just before. The uncertainty is part of why NASA is stepping up efforts to better understand the population of asteroids that come closest to our world.
Scientists discovered asteroid 2024 MK just 13 days before it flew past Earth, 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.
NASA/JPL-Caltech
The mosaic shows 2024 MK as the asteroid rotates in one-minute increments about 16 hours after its closest approach to Earth.
The Asteroid Terrestrial-Impact Last Alert System, or ATLAS, at the Sutherland Observatory in South Africa first spotted the space rock on June 16. While the asteroid is also considered potentially dangerous, it does not appear to be on any worrisome trajectory relative to Earth. anytime soon.
Astronomers have sent radio waves into a space rock and captured a detailed image of asteroid 2024 MK. Thirty-foot-wide (10-meter-wide) boulders cover its surface, as well as concave spots and ridges. The asteroid measures 500 feet (150 meters) across and appears square and elongated, while also having some prominent flat and rounded areas.
As the space rock passed by our planet and encountered Earth’s gravity, its trajectory changed. Now, the asteroid’s 3.3-year journey around the Sun has been shortened by about 24 days.
Objects the size of asteroid 2024 MK only come close to Earth every few decades, so astronomers gathered as much data as they could.
“This was an extraordinary opportunity to explore the physical properties and obtain detailed images of a near-Earth asteroid,” Benner said.