Asteroid Bennu is spitting rocks into space and NASA doesn’t know why
By Sean Keach, The Sun, December 10, 2019
This view of asteroid Bennu ejecting particles from its surface was created by combining two images taken by the NavCam 1 imager aboard NASA's OSIRIS-REx spacecraft. NASA/Goddard/University of Arizona
An enormous asteroid that could one day hit Earth in a devastating impact is mysteriously spitting out rocks.
So-called “doomsday” asteroid Bennu is ejecting meter-sized “particles” into space — and NASA is baffled.
Bennu has achieved infamy after being declared a “hazardous object” by astronomers.
The 1,600-foot asteroid could smash into Earth on several different dates, in an event akin to all-out nuclear war.
Late last year’s NASA’s Osirix-Rex probe arrived at Bennu and began circling it, relaying images and data to space scientists.
And researchers made an unexpected discovery: Bennu was occasionally “discharging” large chunks of material into space.
These particles then either briefly orbited Bennu and fell back onto its surface — or escaped into space.
“No one has ever seen an active asteroid up close like this,” said Carl Hergenrother, an astronomer at the University of Arizona, speaking to Wired.
“It wasn’t that long ago that the conventional wisdom was that asteroids are these dead bodies that didn’t change very much.”
Some of the chunks of material were traveling at 10 feet per second and were blasted out during “ejection events.”
The largest of these events took place on January 6 and saw 200 separate chunks ejected.
“Among Bennu’s many surprises, the particle ejections sparked our curiosity and we’ve spent the last several months investigating this mystery,” said Dante Lauretta, OSIRIS-REx principal investigator at the University of Arizona, Tucson.
“This is a great opportunity to expand our knowledge of how asteroids behave.”
Scientists have several theories about what could be causing the ejection events.
It’s possible that meteoroids are striking Bennu, blasting material up into space.
Thermal stress fracturing — where a change from cold to warm temperatures during the day creates rifts — could also be sparking ejections.
And the release of water vapor sending particles flying is the third theory being discussed.
“It could be that more than one of these possible mechanisms are at play,” said Steve Chesley, an author on the paper and Senior Research Scientist at NASA’s Jet Propulsion Laboratory in Pasadena, California.
“For example, thermal fracturing could be chopping the surface material into small pieces, making it far easier for meteoroid impacts to launch pebbles into space.”
Further examinations should reveal the truth.
Importantly, the Osiris-Rex probe is also due to land on Bennu in 2023, to scoop up samples ahead of its return to Earth.
The other good news is that although Bennu could hit us, it’s unlikely.
“The possibility of Bennu hitting Earth is very low (1 in 3000) and if it does, it will be in 150-200 years time,” said Dr. Robin Smith, a physicist at Sheffield Hallam University, speaking to The Sun earlier this year.
And by then, it’s possible that we’ll have put into place a sci-fi asteroid-blasting weapon to save us from certain doom.
However, an impact by Bennu would be devastating for Earth if it happened.
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