Last week, Earth was treated to a rare event: not one, but two large asteroids that flew past within caller range.
Neither 2024 MK nor 2011 UL21, as the asteroids are named, came close enough to pose a danger, but both were within range of radar imaging systems. So NASA got some lucky pictures on this occasion.
They are more than souvenirs from an asteroid flyby. Scientists can study the images to understand the properties of rocks that can be found near Earth—information that can help us strategize for future asteroids that could one day threaten our planet.
Earth’s little corner of the Solar System is mostly empty, but not completely. The occasional comet or asteroid passes by as it makes its own orbit around the Sun.
The vast majority of them won’t be a problem. But anything that passes within a certain distance of Earth or above a certain brightness is classified as potentially dangerous.
This is because while their current orbit may be fine, something unexpected could happen, such as a collision with another object that puts it on a collision course with Earth. Not likely, but not impossible either.
Both the 2024 MK and the 2011 UL21 were in the potentially hazardous category; luckily for us, no unforeseen craziness knocked them off course in our direction.
2011 UL21 flew by Earth on June 27 at a distance of 6.6 million kilometers (4.1 million miles), about 17 times the distance between Earth and the Moon.
Less than two days later, 2024 MK appeared. On June 29, it flew by at a minimum distance of 295,000 kilometers (184,000 mi). That’s much closer, about three-quarters the distance between the Earth and the Moon.
Visualizing such objects is not exactly easy, even though they are relatively close and are classified as “large” asteroids. In the scheme of things, they’re still pretty small and not very bright.
That’s why NASA uses a large radar telescope to transmit radio waves into space and receive a signal back from which scientists can create images.
Because 2024 MK was much closer—an asteroid flyby that close only happens every few decades—we were able to get much more detailed images.
NASA used one telescope to transmit radio waves and another to receive them, resulting in images of 2024 MK that include not only the shape of the asteroid, but also bumps, depressions, boulders and ridges.
It measures roughly 150 meters (500 ft) across and has an elongated shape with lots of flat planes. It also collapses when moving through space.
It was only discovered on June 16, and its orbit has been altered by Earth’s gravity, so the observation allows scientists to see what 2024 MK will do in the future. They revealed that it will be safely out of our way for the foreseeable future. Yuck.
“This was an extraordinary opportunity to study the physical properties and obtain detailed images of a near-Earth asteroid,” says astronomer Lance Benner of NASA’s Jet Propulsion Laboratory.
2011 UL21, at its much greater distance, did not return images that were as detailed… but these images contained a small surprise. There, astronomers accompanying the 1.5-kilometer-wide asteroid spotted a small moon in an orbit of about 3 kilometers.
This is something we find more and more with large asteroids.
Last year, asteroid Dinkinesh, an object in the asteroid belt visited by NASA’s Lucy probe, was discovered with a small moon. And NASA’s famous Double Asteroid Redirect Test, in which a spacecraft was smashed into an asteroid, was conducted on Dimorphos, the smaller of the binary asteroid pair.
We’re finding more binary asteroids as our imaging capabilities improve, and that’s great news for planetary defense and our understanding of solar system evolution.
“About two-thirds of asteroids of this size are thought to be binary systems,” says Benner, “and their discovery is particularly important because we can use measurements of their relative positions to estimate their relative orbits, masses, and densities, which provide key information about , how they could have arisen.”
And they are so damn cute. Hi, friend. Fly anytime.