Damocloids are 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 Comet Halley, but without showing a cometary coma or tail.
Damocloids are believed to be nuclei of Halley-type comets that have lost all their volatile materials due to outgassing and become dormant. Such comets are believed to 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.) David Jewitt defines a damocloid as an object with a Tisserand's parameter relative to Jupiter TJ ≤ 2. This can also loosely be defined as (q < 5.2 AU, a > 8.0 AU, and e > 0.75) or i > 90 deg, but this definition that does not focus on Jupiter excludes objects such as (127546) 2002 XU93, 2003 WG166, and 2004 DA62.
Using the Tisserand parameter (T-Jupiter < 2) there are currently 81 damocloid candidates, and about half of them still have poorly known orbits. Of these objects, 42 have orbital observation arcs greater than 30 days providing reasonably decent orbits.
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.
- David Jewitt (2011 Feb). "The DAMOCLOIDS". UCLA, Department of Earth and Space Sciences. Retrieved 2011-02-09. (Current list at JPL Small-Body Database Search Engine / 2011 list / 2010 list)
- Akimasa Nakamura and bas (2009-05-02). "List of Damocloids (Oort cloud asteroids)". Lowell Observatory. Retrieved 2011-02-09.
- Jewitt, David (2005). "A first look at the Damocloids". The Astronomical Journal 129 (1): 730–538. Bibcode:2005AJ....129..530J. doi:10.1086/426328. Retrieved 2011-02-13.
- "JPL Small-Body Database Search Engine: asteroids and T-Jupiter < 2". JPL Solar System Dynamics. Retrieved 2011-02-11. Search parameters used: Limited by object type/group: Asteroids and T-Jupiter < 2
- "NEO Close-Approaches (Between 1900 and 2200)". NASA/JPL Near-Earth Object Program. Retrieved 2011-02-09. (sorted by descending relative velocity, dist<0.5AU = "186,491 close-Earth approaches")
- David Jewitt, A first look at the Damocloids