Last week, Earth was treated to a rare event: not one, but two large asteroids, passing within striking distance.
Neither 2024 MK nor 2011 UL21, as the asteroids are called, came close enough to pose a danger, but both were within range of radar imaging systems. So NASA took some happy photos to mark the occasion.
These are more than just asteroid souvenirs. Scientists can study the images to understand the properties of rocks that might be found near Earth — information that could help us put together strategies for any future asteroids that might one day threaten our planet.
Earth’s little corner of the Solar System is mostly empty, but not completely. The occasional comet or asteroid floats by as it makes its revolving orbit around the Sun.
The vast majority of them will not be a problem. But anything that passes within a certain distance from Earth, or is above a certain brightness, is classified as potentially dangerous.
This is because, even though their current path may be good, something unexpected can happen, such as a collision with another object that knocks it on a collision course with Earth. It’s not likely, but not impossible either.
Both 2024 MK and 2011 UL21 were in the potentially hazardous category; luckily for us, no unforeseen madness knocked them off our course.
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.
Then, less than two days later, 2024 MK appeared. On June 29, it passed a minimum distance of 295,000 kilometers (184,000 miles). That’s much closer, about three-quarters of the distance between the Earth and the Moon.
Imaging such objects is far from easy, even when they are relatively close and are classified as “large” asteroids. They are still pretty small in the scheme of things, and not very bright.
That’s why NASA uses a large radar telescope to transmit radio waves into space and receive the signal back from which scientists can build images.
Because 2024 MK was so much closer – such close proximity for an asteroid flyby only happens every few decades or so – we were able to get much more detailed images.
NASA used one telescope to transmit the radio waves and a second to receive them, resulting in images of 2024 MK that include not only the shape of the asteroid, but bumps, dents, rocks and ridges.
It is approximately 150 meters (500 feet) wide and has an elongated shape with many flat planes. It also falls as it moves through space.
It was only discovered on June 16, and its orbital path was altered by Earth’s gravity, so observations allow scientists to understand what 2024 MK will do in the future. They found that for the foreseeable future, it will stay safely out of our way. Phew.
“This was an incredible opportunity to investigate 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, didn’t return images that were as detailed… but those images included a little surprise. There, accompanying the 1.5-kilometer-wide asteroid, astronomers spotted a small moon at an orbital distance of about 3 kilometers.
That’s something we’re finding more and more with large asteroids, actually.
Last year, asteroid Dinkinesh, an object in the asteroid belt visited by NASA’s Lucy probe, was discovered to have a small moon. And NASA’s famous Double Asteroid Redirect Test, in which a spacecraft crashed into an asteroid, was conducted on Dimorphos, the smaller of a binary asteroid pair.
We’re finding more binary asteroids because our imaging capabilities are improving, and that’s great news for planetary defense and our understanding of the evolution of the Solar System.
“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 mutual orbits, masses and density, which provide key information about how they may have formed.”
And they are just so cute. Hey there lil buddy. Fly anytime.