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NASA’s OSIRIS-REx spacecraft arrived at asteroid Bennu in December 2018, and just one week later, it discovered something unusual about Bennu: the asteroid was ejecting particles into space.
The spacecraft’s navigation camera first spotted the particles, but scientists initially thought they were just stars in the background. After closer scrutiny, the OSIRIS-REx team realized they were particles of rock, and were concerned that they might pose a hazard.
Asteroids - Mass - Asteroids - Comets - Trails
Asteroids that are losing mass are called “active asteroids” and sometimes “main-belt comets.” They sometimes leave transient trails of dust and debris that looks like a comet’s tail. When these types of asteroids were first observed, astronomers thought that the trail was made of melting ice, like a comet’s tail. But now we know that there are several mechanisms that can cause an asteroid to be active.
Mass-shedding asteroids are sometimes called “Main-belt comets” because in telescope images they have tails like comets. Image Credit: Jewitt et al, 2012.
Astronomers - Asteroids - Material - Telescopes - Asteroids
Astronomers haven’t found many active asteroids, and most of them are losing so much material that it’s visible in telescopes. Most asteroids are stable, and in fact, Bennu appeared to be an inactive asteroid in Earth-based observations. Naturally, scientists working with OSIRIS-REx wanted to know more, and stumbling on one with the spacecraft presented an unplanned opportunity to study one of these asteroids up close.
“This is a great opportunity to expand our knowledge of how asteroids behave.”
Prof - Dante - Lauretta - Principal - Investigator
Prof. Dante Lauretta, Principal Investigator, OSIRIS-REx Mission.
“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,” he said in a press release.
Variety - Causes - Asteroids - Bennu - Ice
There are a variety of causes for active asteroids like Bennu. Sublimating ice, impacts, rotational...
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