NASA Releases Images of Large Asteroids That Just Sailed Past Earth: ScienceAlert

Last week, Earth was treated to a rare event: not one, but two large asteroids passing within earshot.

Neither 2024 MK nor 2011 UL21, as the asteroids are known, came close enough to pose a threat, but both were within range of radar systems, so NASA got a few happy snapshots to mark the occasion.

These are more than just souvenirs from an asteroid flyby. Scientists can study the images to understand the properties of rocks found near Earth — information that can help us plan strategies for future asteroids that could one day threaten our planet.

Earth’s tiny corner of the solar system is mostly empty, but not entirely. Every now and then a comet or asteroid flies by, making its own looping orbit around the sun.

The vast majority of these will not be a problem. However, anything that passes within a certain distance of the Earth, or is above a certain brightness, is classified as potentially hazardous.

Some images of asteroid 2024 MK. (NASA/JPL-Caltech)

That’s because even if their current path is fine, something unexpected could happen, like a collision with another object that puts them on a collision course with Earth. It’s not likely, but it’s not impossible either.

Both 2024 MK and 2011 UL21 were in the potentially dangerous category. Fortunately for us, they were not blown off course by any unexpected madness.

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 flew by at a minimum distance of 295,000 kilometers (184,000 miles). That’s much closer, about three-quarters of the distance between Earth and the moon.

It’s not exactly easy to image such objects, even if they are relatively close and classified as “large” asteroids. They are still quite small in the grand scheme of things, and not very bright.

That’s why NASA uses a large radar telescope to send radio waves into space and receive the return signal, which scientists use to construct images.

The complete set of MK images from 2024. (NASA/JPL-Caltech)

Because 2024 MK was much closer – such a close approach for an asteroid to pass by only happens once every few decades – we were able to obtain much more detailed images.

NASA used one telescope to transmit the radio waves and a second to receive them. The resulting images of 2024 MK show not only the asteroid’s shape, but also bumps, dimples, boulders and ridges.

It measures about 150 meters (500 feet) in diameter and has an elongated shape with many flat surfaces. It also tumbles as it moves through space.

It was only discovered on June 16th and its orbit has been altered by Earth’s gravity, so the observations allow scientists to figure out what 2024 MK will do in the future. They revealed that it will stay safely out of our way for the foreseeable future. Phew.

“This was an extraordinary opportunity to study the physics of a close-to-Earth asteroid and obtain detailed images,” said astronomer Lance Benner of NASA’s Jet Propulsion Laboratory.

2011 UL21, at its much greater distance, didn’t yield images quite as detailed… but those images did contain a small surprise. There, along with the 1.5-kilometer-wide asteroid, astronomers spotted a tiny moonlet, at an orbital distance of about 3 kilometers.

Images from 2011 UL21, showing its tiny moon. (NASA/JPL-Caltech)

This is something we are seeing more and more with large asteroids.

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 Redirection Test, in which a spacecraft collided with an asteroid, was performed on Dimorphos, the smaller of a binary asteroid pair.

We are finding more and more binary asteroids as our imaging capabilities improve, which is excellent news for planetary defense and for our understanding of the evolution of the solar system.

“About two-thirds of asteroids this size are thought to be binary systems,” Benner said. “Their discovery is significant because we can use measurements of their relative positions to estimate their orbits, masses and densities, which give us important information about how they might have formed.”

And they’re just so damn cute. Hey there, little buddy. Fly right on over.

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