A composite image of a short and long exposure photograph of Bennu showing the largest particle ejection on January 6, 2019.
Enlarge / A composite picture of a brief and lengthy publicity {photograph} of Bennu exhibiting the most important particle ejection on January 6, 2019.

NASA | Goddard | University of Arizona | Lockheed Martin

For the final yr, NASA’s OSIRIS-REx spacecraft has been circling a big asteroid named Bennu that repeatedly passes uncomfortably near Earth. The spacecraft has been painstakingly mapping the asteroid’s rocky floor utilizing a collection of cameras and different devices that may assist it decide the place to land subsequent yr. Once NASA selects a remaining touchdown website, OSIRIS-REx will kiss Bennu simply lengthy sufficient to scoop up a pattern to convey again to Earth in 2023.

Many scientists anticipate the Bennu pattern to revolutionize our understanding of asteroids, particularly those who are close to Earth and pose the best menace from area to life as we all know it. But as detailed in a paper printed this week in Science, NASA has already began making stunning discoveries round this alien world. Earlier this yr, the OSIRIS-REx workforce witnessed particles exploding from the asteroid’s floor—and it’s unsure why.

“No one has ever seen an active asteroid up close like this,” says Carl Hergenrother, an astronomer on the University of Arizona and the scientist who proposed Bennu because the goal for OSIRIS-REx. “It wasn’t that long ago that the conventional wisdom was that asteroids are these dead bodies that didn’t change very much.”

No one knows why rocks are exploding from asteroid Bennu 1

In January, the navigation cameras on OSIRIS-REx captured three ejection occasions that every spewed about 100 centimeter-sized asteroid particles into area. The spacecraft additionally detected a big variety of particles orbiting Bennu like a cloud of gnats. Their various orbits recommend that particle ejections are a typical occasion on the asteroid and happen all throughout its floor, quite than in a number of choose spots. Indeed, within the yr for the reason that three ejection occasions that are reported in the present day in Science, Hergenrother says OSIRIS-REx has detected a number of different smaller ejections.

Asteroid Bennu isn’t actually “alive” as a result of it doesn’t have a heated core essential for geological exercise, however as Hergenrother and his colleagues found, it’s not precisely lifeless both. It’s an area zombie roaming the photo voltaic system, sneezing out small rocks. Some rapidly return to the floor like a cannonball, whereas others escape into the huge vacancy of deep area. But what’s actually intriguing, says Hergenrother, are the rocks that find yourself in orbit round Bennu and turn out to be miniature moons for a number of days earlier than returning to the floor.

“What we’re seeing is something we would have never been able to see from the ground,” Hergenrother provides. “So the question that is still on our minds is are we seeing a lower intensity process that is similar to what happens on other active asteroids, or is this something entirely different?”

Scientists have seen huge ejections from about two dozen asteroids as they go by Earth, however the mechanisms invoked to clarify why these asteroids are ejecting materials don’t work for Bennu. The centrifugal pressure of an asteroid’s spin, for instance, may eject materials from the floor, however it will possibly’t account for the vary of particle orbits seen by OSIRIS-REx. Likewise, the sublimation of ice water—the identical phenomenon that produces a comet’s tail—can’t clarify what’s occurring on Bennu as a result of OSIRIS-REx witnessed particle ejections on components of Bennu that get means too scorching to host ice.

Hergenrother says the OSIRIS-REx workforce has narrowed the thriller to 2 attainable causes. One potential perpetrator is the intense temperatures on Bennu, which vary from 240° to -100° Fahrenheit. The stress from this transition may cause particles to crack and fly aside like popcorn. Another chance is that Bennu is getting bombarded with micrometeoroids that kick up the particles after they strike the floor.

Unfortunately, OSIRIS-REx gained’t be hanging round Bennu lengthy sufficient to resolve the thriller by itself, in keeping with Hergenrother. There is much more science to be finished earlier than the spacecraft departs for Earth, so the thriller of Bennu’s particle eruptions may need to be shelved—for now.

But given how little we find out about asteroids, Hergenrother says there’s a powerful case to be made for a devoted mission to review the phenomenon on one other asteroid sooner or later.

This story initially appeared on wired.com.


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