back to article Asteroid Bennu is flinging particles of dust and rock from its surface – and scientists can't work out why

A closeup image of Bennu snapped by NASA's OSIRIS-REx spacecraft reveals that the asteroid's surface is surprisingly volatile, randomly spitting out shards of debris into space. Researchers call these episodes particle ejection events. "Among Bennu's many surprises, the particle ejections sparked our curiosity, and we've …

  1. ThatOne Silver badge

    Space Dandruff

    I would think it's easy to determine if the cause is impacting meteorites, since debris would only be rising from specific spots at a time. If they rise from all over the place at the same time it must be something local and generalized which propels them, although it must be quite energetic to fling 10 cm rocks at 3 m/s. I'm no specialist but that sounds more like an explosion than the gentle push of random water vapor releases.

    I guess the only way to know is to get a closer look?

    1. Tom 7 Silver badge

      Re: Space Dandruff

      This has been interstellar for a very long time. So its been around 4K for a long time, slowly accumulating debris at around that temperature. Now imagine it comes near a sun and gets warmed up a couple of hundred K and a 10cm piece of rock expands just a bit more than the substrate its embedded in. I've seem bits of concrete raised by similar temperatures travel several tens of meters on earth though that may be assisted by additional vapour pressure but man selects special materials for around fire places for a good reason.

      1. Brewster's Angle Grinder Silver badge

        Space is hotter than you think

        Bennu isn't an interstellar object; it's local rubbish. So it will have enjoyed a balmy couple of hundred kelvin for most of its life and never known the chill "4K" of the interstellar medium - obviously varying with it's distance form the sun and with strong diurnal variation between day side and night side.

        1. Tom 7 Silver badge

          Re: Space is hotter than you think

          My apologies - I thought Bennu was the less Nazi name for the interstellar thingy. We have too many minor minor minor planets and need to name these thing scientifically with canonical cataloguing numbers or database SQL clauses that can be entered directly into my scope so it will spin round and knock me on the head as I try and find something in the spotting scope.

      2. ThatOne Silver badge

        Re: Space Dandruff

        > imagine it comes near a sun and gets warmed up a couple of hundred K and a 10cm piece of rock expands just a bit more than the substrate its embedded in.

        Except Bennu is (AFAIK) a pile of gravel, and everything should just shuffle about as the gravel expands and contracts. What concentrates the energy enough to be able to fling a 10 cm rock at 3 m/s?

    2. TrumpSlurp the Troll

      Re: Space Dandruff

      Possibly worth considering the executive toy of the 5 suspended steel balls.

      Hit one end and something flies off the other end.

      In that case it is one or more steel balls.

      Where the far side from the impact is just loose stuff it doesn't seem unlikely that a point impact would generate a shock wave which impacted a wide area on the opposite side and sprayed a load of gravel around.

      I am reminded of the original Day of the Jackal which shows the sighting in of a rifle using a water melon as a target. Direct hit and bits flew everywhere.

      1. ThatOne Silver badge

        Re: Space Dandruff

        > Possibly worth considering the executive toy of the 5 suspended steel balls.

        Except Bennu is (AFAIK) a pile of gravel, there is no elastic transfer of energy. Each time you plant a pickax in the ground, Chinese don't see pebbles jumping into the air...

    3. Mark 85 Silver badge

      Re: Space Dandruff

      Dandruff would be better than it actually being alive and those are eggs being released. Yeah.. I've read too much science fiction... so back to my room.

  2. HildyJ Silver badge

    Space baboons

    Much as Earth baboons fling feces at the people observing them in zoos, space baboons on Bennu have gotten tired of the observations and started flinging rocks in protest. Case closed.

    1. spold Silver badge

      Re: Space baboons

      I'm afraid I cannot agree - it's burrowing Space Rabbits. Bennu is misheard... should be Bunny.

  3. Francis Boyle Silver badge


    You write an article about "ejection events" and you didn't go there.

  4. sbt

    ... in the late afternoon

    When your day is only 4 hours long, the ejections will be over pretty quickly.

  5. Anonymous Coward
    Anonymous Coward

    Clearly, there is some one defending Bennu against the alien space invaders

    1. Doctor Syntax Silver badge

      Nah, it's just litter louts. Look carefully & you'll find it's all bits of polystyrene cups, crisp packets & sweet wrappers.

  6. Blofeld's Cat Silver badge

    Er ...

    Perhaps Magrathea should have stuck to high-end planets and not tried to introduce a budget option ...

    "Look, I've only had the thing a couple of millennia and now all the surface is coming unstuck."

    1. Venerable and Fragrant Wind of Change

      Re: Er ...

      Shirley that's not Magrathea, it's the cheap knock-off!

      My house emits space dust, too. It's hard work for the vacuum cleaner.

  7. Empire of the Pussycat

    baby clanger

    teasing the soup dragon

  8. 89724102172714182892114I7551670349743096734346773478647892349863592355648544996312855148587659264921 Bronze badge

    Particles flung from the surface of Uranus must be avoided

  9. Chris G Silver badge


    The ship has been observing the solar system for a few millenia and is decloaking prior to returning to report that once again it has failed to observe intelligent life in a system.

  10. Pascal Monett Silver badge

    It's going to be interesting reading about how they solve this mystery

    Space is decidedly awesome. Last year that rubber ducky-shaped asteroid we put a lander on actually demonstrated landslides, now we have an asteroid that ejects solid matter without a volcano.

    Explaining that is going to take some serious genius. I can't wait for the result.

  11. phuzz Silver badge

    They flew too close and now whatever lives inside is waking up. It's hatching...

  12. MrKrotos

    particle ejection events

    Sounds like a typical youths weekend

  13. x 7


    I thought you needed river systems to deposit clay?

  14. Andy E

    Its having a....

    Its having a PEE (Particle Ejection Event). Please give it some privacy.

  15. Claptrap314 Silver badge

    Covering all the options, huh?

    "The particles were flung out at a maximum speed of three meters per second from different regions of the asteroid; they either ended up in orbit around the asteroid, crashed back down onto its surface, or floated away into space."

    I mean, they could be colliding with each other & breaking into smaller bits. They might evaporate in the solar wind. Some might find shade and set up a haven of sorts...

  16. Anomalous Cowshed

    3 m / second

    That's about 11 km / hour. Not exactly stellar the thing rotating? Is something crashing into it? Is it moving through space? Then 3 m / second is a quantity that can be described as a mere error correction.

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