Imagine you are traveling through space, minding your own business, in your own lane, then this asteroid passes by and spits out pebbles at you!! shocking as it seems, According to new research a meteorite on Earth holds scars as a proof of some asteroids shooting out pebbles.
Back in 2019, NASA’s OSIRIS-REx spacecraft captured images of a strange mysterious never seen before phenomenon no – Asteroid Bennu shooting out swarms of marble-sized rocks.
Aguas Zarcus, a meteorite named after a Costa Rican city it landed in 2019, researchers studying the space rock found something strange. “We were trying to isolate very tiny minerals from the meteorite by freezing it with liquid nitrogen and thawing it with warm water, to break it up,” says Yang, a graduate student at the Field Museum and the University of Chicago and the paper’s first author. “That works for most meteorites, but this one was kind of weird– we found some compact fragments that wouldn’t break apart.”
Finding bits and pieces of meteorites that won’t disintegrate was never heard off, but the researchers kept an open mind and devised a plan to figure out the composition of these pieces. “We did CT scans to see how the pebbles compared to the other rocks making up the meteorite,” says Philipp Heck, the Robert A. Pritzker Curator of Meteoritics at Chicago’s Field Museum and the senior author of the Nature Astronomy study. “What was striking is that these components were all squished– normally, they’d be spherical– and they all had the same orientation. They were all deformed in the same direction, by one process.” Something had happened to the pebbles that didn’t happen to the rest of the rock around them.
Excited and curious the researchers put together a hypothesis involving the 2019 OSIRI-REx findings, they supported the hypothesis with physical models. The asteroid underwent a high-speed collision, and the area of impact got deformed. That deformed rock eventually broke apart due to the huge temperature differences the asteroid experiences when it rotates, since the side facing the sun is more than 300° F warmer than the side facing away. “This constant thermal cycling makes the rock brittle, and it breaks apart into gravel,” says Heck.
These pebbles are then ejected from the asteroid’s surface. “We don’t yet know what the process is that ejects the pebbles,” says Heck– they might be dislodged by smaller impacts or other space collisions, or they might just get released by the thermal stress the asteroid undergoes. But once the pebbles are disturbed, Heck says, “you don’t need much to eject something– the escape velocity is very low.” A recent study of Bennu revealed that its surface is loosely bound and behaves like popcorn in a bucket.
The pebbles then entered a very slow orbit around the asteroid, and eventually, they fell back down to its surface further away where there was no deformation. Then, Heck and Yang say, the asteroid underwent another collision, the loose mixed pebbles on the surface got transformed into solid rock. “It basically packed everything together, and this loose gravel became a cohesive rock,” says Heck. The same impact may have dislodged the new rock, sending it careening into space. Eventually, that chunk fell to Earth as the Aguas Zarcas meteorite, carrying evidence of the pebble mixing.
Aguas Zarcas is the first meteorite to show signs of this behavior, but it’s probably not the only one. “We would expect this in other meteorites,” says Heck. “People just haven’t looked for it yet.”