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Damocloids are a class of minor planets such as 5335 Damocles and 1996 PW that have Halley-family or long-period highly eccentric orbits typical of periodic comets such as Halley's Comet, but without showing a cometary coma or tail. David Jewitt defines a damocloid as an object with a Tisserand's parameter relative to Jupiter of 2 or less (TJ ≤ 2),[1] while Akimasa Nakamura defines this group with the following orbital criterion:[2]

  • q < 5.2 AU, a > 8.0 AU, and e > 0.75,
  • or alternatively, i > 90°

However, this definition that does not focus on Jupiter excludes objects such as (127546) 2002 XU93, 2003 WG166, and 2004 DA62.[3]

Using the Tisserand's parameter with respect to Jupiter of 2 or less, there are currently 155 damocloid candidates.[4] Of these objects, 122 have orbital observation arcs greater than 30 days providing reasonably decent orbits.[5][1] Their average radius is eight kilometers assuming an albedo of 0.04. The albedos of four damocloids have been measured, and they are among the darkest objects known in the Solar System. Damocloids are reddish in color, but not as red as many Kuiper-belt objects or centaurs. Other damocloids include: 2013 BL76, 2012 DR30, 2008 KV42, (65407) 2002 RP120, and 20461 Dioretsa.

Retrograde objects such as Halley's Comet and damocloid (343158) 2009 HC82 can have relative velocities to Earth of 81 km/s (290,000 km/h).[6]


Damocloids are thought to be nuclei of Halley-type comets that have lost all their volatile materials due to outgassing and become dormant. Such comets probably originate from the Oort cloud. This hypothesis is strengthened by the fact that a number of objects thought to be damocloids (and assigned minor-planet provisional designations) subsequently showed a coma and were confirmed to be comets: C/2001 OG108 (LONEOS), C/2002 CE10 (LINEAR), C/2002 VQ94 (LINEAR), C/2004 HV60 (Spacewatch) and possibly others. Another strong indication of cometary origin is the fact that some damocloids have retrograde orbits, unlike any other minor planets. (Objects with an inclination beyond 90 degrees up to 180 degrees are in a retrograde orbit and orbit in the opposite direction of other objects.)

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  1. ^ a b David Jewitt (August 2013). "The DAMOCLOIDS". UCLA, Department of Earth and Space Sciences. Retrieved 2014-02-14.  (2013 list / 2011 list / 2010 list)
  2. ^ Akimasa Nakamura and bas (2 May 2009). "List of Damocloids (Oort cloud asteroids)". Lowell Observatory. Retrieved 15 February 2017. 
  3. ^ Jewitt, David (2005). "A first look at the Damocloids" (PDF). The Astronomical Journal. 129 (1): 530–538. Bibcode:2005AJ....129..530J. doi:10.1086/426328. Retrieved 2011-02-13. 
  4. ^ "JPL Small-Body Database Search Engine: asteroids and T-Jupiter <= 2". JPL Solar System Dynamics. Retrieved 2017-02-20.  Search parameters used: Limited by object type/group: Asteroids and T-Jupiter <= 2
  5. ^ "JPL Small-Body Database Search Engine: asteroids and T-Jupiter <= 2 and data-arc span > 30 (d)". JPL Solar System Dynamics. Retrieved 2017-11-07. 
  6. ^ "NEO Close-Approaches (Between 1900 and 2200)". NASA/JPL Near-Earth Object Program. Retrieved 2012-06-22.  (sorted by descending relative velocity, dist<0.5AU = "215,221 close-Earth approaches")

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