331P/Gibbs (P/2012 F5) is a small periodic Encke-type and rare main-belt comet, discovered by American amateur astronomer Alex Gibbs.[2]

331P/Gibbs (P/2012 F5)
Discovered byA. R. Gibbs
(Mount Lemmon Survey)
Discovery dateMarch 22, 2012
Orbital characteristics A
Epoch4 February 2012 (JD 2455961.5)
Observation arc11.3 years
No. of observations used148
Aphelion3.130 AU
Perihelion2.877 AU
Semi-major axis3.004 AU
Orbital period5.21 years (1902 days)
Earth MOID1.88 AU
Jupiter MOID2.08 AU
Dimensions~2-5 km
Comet total
magnitude (M1)
Comet nuclear
magnitude (M2)
Last perihelion16 June 2015
Next perihelion29 September 2020[1]


It is a rare type of comet called a main-belt comet. Although most comets come from the Oort cloud or the Kuiper belt, main-belt comets are instead members of the asteroid belt that have a coma and tail. As of 2016, it is one of only 15 known main-belt comets.[3]

Precovery observations of 331P/Gibbs in Sloan Digital Sky Survey data were found dating to August 2004, in which the object was visible as a regular asteroid. Further observations in 2014 by the Keck Observatory showed that the comet was fractured into 5 pieces and rotating rapidly, with a rotation period of only 3.2 hours. Due to the YORP effect, P/2012 F5 had begun to spin so quickly that, being a likely rubble pile, parts began to be thrown off, leaving a very long dust trail.[4] This is very similar to 311P/PANSTARRS, being the best-established cause for main-belt comets along with impacts between small asteroids (such as with 596 Scheila and P/2010 A2 (LINEAR)).


  1. ^ MPC
  2. ^ "JPL Small-Body Database Browser: (331P/Gibbs)" (last observation: 2015-12-14).
  3. ^ "JPL Small-Body Database Search Engine". Jet Propulsion Laboratory. NASA. Retrieved 10 December 2016.
  4. ^ "Active asteroid spun so fast that it exploded". Astronomy Now. Retrieved 10 December 2016.

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