The asteroid NASA just landed on turns out to be hollow, with a large 'void' at its center. It may be spinning itself to death.

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The asteroid NASA just landed on turns out to be hollow, with a large 'void' at its center. It may be spinning itself to death.
A rotating mosaic of asteroid Bennu, composed of images captured by NASA’s OSIRIS-REx spacecraft over a four-hour period on December 2, 2018.NASA/Goddard/University of Arizona
  • NASA's Osiris-Rex spacecraft recently touched down on an asteroid called Bennu and sucked up a sample from its surface.
  • The probe has been orbiting Bennu for two years.
  • Now its data shows that Bennu is hollow.
  • The space rock is spinning rapidly, pushing its material out toward its surface. It could eventually spin itself to pieces.

The asteroid Bennu just keeps getting more bizarre.

When NASA decided to send a probe to land on a space rock and bring back samples, it picked Bennu for its seemingly smooth surface — perfect landing ground. But once the Osiris-Rex spacecraft had made the 200-million-mile journey to Bennu, the images it beamed back revealed a landscape covered in boulders and rock fields.

NASA eventually chose the flattest spot it could find to land, and the touch-and-go operation to scoop up material went smoothly last month. But then came the next surprise: Bennu's rock turned out to be incredibly soft, crumbling under the spacecraft as it touched the surface.

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The probe fired a blast of nitrogen to send rock and dust swirling — that way it could catch some in its sample-collection tool. But yet again, scientists were caught off-guard when the maneuver turned out to have yielded so much material that dust and rock were propping the sample-collection tool open, allowing precious alien dust to leak into space.

They managed to stow the sample before losing too much, but that wasn't the last of the shocks. Recently, University of Colorado researchers concluded based on data Osiris-Rex has collected in the two years it's been circling Bennu that the asteroid is probably hollow.

"It's as if there is a void at its center, within which you could fit a couple of football fields," Daniel Scheeres, a professor in the university's Department of Aerospace Engineering Sciences who led the research, said in a press release.

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What's more, Bennu could be spinning itself to pieces.

'The whole thing flying apart'

While Osiris-Rex has been orbiting Bennu, the probe has measured how much the asteroid's gravity pulled on it. At the same time, Bennu was also flinging marble-sized bits of rock away from its surface. Those crumbs entered orbit around the asteroid, then some of them fell back to its surface. By tracking their motions, mission managers were able to make calculations about the strength of Bennu's gravity.

Since gravity comes from mass, these two sets of data allowed Scheeres' team to calculate how material is distributed through the inside of the asteroid.

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Their findings, published in the journal Science Advances on October 8 (before Osiris-Rex's brief landing), show that it's far from even. The force of the Bennu' spinning seems to be pushing its material outward towards the surface. Some of the thinnest parts of the asteroid are at its bulging equator.

Bennu completes one rotation every four hours, and it's only getting faster.

"You could imagine maybe in a million years or less, the whole thing flying apart," Scheeres said.

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Bennu could hold secrets about the origins of life

The asteroid NASA just landed on turns out to be hollow, with a large 'void' at its center. It may be spinning itself to death.
An illustration of OSIRIS-REx in orbit around asteroid Bennu.NASA’s Goddard Space Flight Center/Conceptual Image Lab

Bennu is one of the most potentially hazardous asteroids in our solar system, according to Osiris-Rex principal investigator Dante Lauretta, since it has a "non-negligible chance" of crashing into Earth during the 22nd century. Its fragility could be good news, though.

Studying Bennu could help future scientists make a plan to divert the asteroid if it ever threatens to impact Earth. The research could also reveal new details about the lives of asteroids — primordial piles of rock that coalesced from the leftover bits that didn't make it into planets. Such objects could hold secrets to how our solar system formed and how life arose on Earth.

"We were hoping to find out what happened to this asteroid over time, which can give us better insight into how all of these small asteroids are changing over millions, hundreds of millions, or even billions of years," Scheeres said. "Our findings exceeded our expectations."

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Osiris-Rex has collected heaps of data that scientists have yet to comb through. The sample it collected is expected back on Earth in 2023.

The asteroid NASA just landed on turns out to be hollow, with a large 'void' at its center. It may be spinning itself to death.
An animation shows OSIRIS-REx releasing its Sample Return Capsule for touchdown in the Utah desert on September 24, 2023.NASA/Goddard/CI Lab

Assuming that the capsule holding the sample safely parachutes into the Utah desert as planned in a few years, NASA has said it will preserve a portion of the alien rock for future study with technologies not yet developed. The agency will ship the rest to laboratories all over the world.

"This is all about understanding our origins, addressing some of the most fundamental questions that we ask ourselves as human beings," Lauretta said before Osiris-Rex landed on the asteroid. "Where did we come from? And are we alone in the universe?"

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