Rock comet

A rock comet is a rare type of small Solar System body that exhibits features of both a comet and an asteroid, mainly in that it outgasses material primarily made up of grains of rock.

The cause of rock comets' outgassing is similar to how mud in a dry lake bottom cracks.

Rock comets, unlike other comets, which outgas primarily ice, have a nucleus made of rock. As a result, they can 'outgas' fairly unpredictably, not just when within the frostline.<ref name==frostline>LASP. "How Planets Form". The Outer Planets. Laboratory for Atmospheric and Space Physics (LASP). Retrieved 7 February 2014. </ref>

The reason this happens is thought to be similar to how mud cracks at the bottom of a dry lake bed, leaving small chunks loose on the surface of the body, which later get pushed off of it due to radiation pressure sweeping.[1]

Sometimes, an object can be mistakenly identified as a rock comet, such as P/2010 A2, an asteroid in the asteroid belt that collided with another object, causing it to have a field of debris trailing it for a short time.[2]

Rock comets are rare because a rocky small Solar System body must come very close to the Sun, close enough for both the solid ground to crack, and for there to be enough energy for the separate pieces to be pushed off of the asteroid. However if the asteroid is close enough to the Sun for the former to happen, the latter will also happen.

Examples

The only known example of a rock comet is 3200 Phaethon, which has a perihelion (closest point to the Sun) closer than any other named asteroid (0.14 AU). It has been known to brighten on occasions, implying outgassing, and has been observed ejecting dust by the STEREO spacecraft.[3][4]

Some unnamed asteroids travel closer to the Sun than 3200 Phaethon, but none have been observed to outgas, which does not imply they do not, because none of these have been observed in detail, and it is possible that detailed observations could show some outgassing.

References

  1. ↑ Sutherland, Paul (10 September 2013). "Why an asteroid is crumbling into meteor dust". Skymania. Retrieved 7 February 2014.
  2. ↑ Harrington, J.D.; Ray Villard (2 February 2010). "Suspected Asteroid Collision Leaves Trailing Debris". www.nasa.gov. NASA. Retrieved 8 February 2014.
  3. ↑ Jewitt, David; Li, Jing; Agarwal, Jessica (17 June 2013). "The Dust Tail of Asteroid (3200) Phaethon". arXiv.org. pp. 2–3. Retrieved 8 February 2014.
  4. ↑ Jewitt, David; Jing Li (14 September 2010). "Activity in Geminid Parent (3200) Phaethon". arXiv. Retrieved 8 February 2014.
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