Damocloid

Damocloid

Damocloid

Class of minor planets


Damocloids are a class of minor planets such as 5335 Damocles and 1996 PW that have Halley-type 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 Jupiter Tisserand invariant (TJ) of 2 or less,[1][lower-alpha 1] while Akimasa Nakamura defines this group with the following orbital elements:[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 220 damocloid candidates as of January 2022.[4] Of these objects, 189 have orbital observation arcs greater than 30 days providing reasonably decent orbits.[1][5] 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.[citation needed] Damocloids are reddish in color, but not as red as many Kuiper-belt objects or centaurs. Other damocloids include: 2013 BL76, 2012 DR30, (528219) 2008 KV42, (65407) 2002 RP120, and 20461 Dioretsa.

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

Origin

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.)

List

As of August 2021 this list from the JPL SBDB contains 20 numbered and 268 unnumbered bodies that meet Akimasa Nakamura's criteria for being classified as a damocloid, that is, either a retrograde orbit, or the following orbital elements: q < 5.2 AU, a > 8.0 AU, and e > 0.75 (also see § top). Tisserand's parameter with respect to Jupiter (TJupiter) is also given.[lower-alpha 1] Akimasa Nakamura's criteria and a TJupiter of less than two are largely equivalent as only a few listed bodies do not meet the defined TJupiter threshold. Most damocloids are also listed on MPC's list of other unusual minor planets.[7] The orbital data is sourced from JPL-numbered and -unnumbered element files.[8] The list includes A/-designated objects (introduced in 2017) that were mistakenly identified as a comet, but are actually minor planets. However it excludes hyperbolic bodies such as A/2019 G4 as well as 1I/ʻOumuamua and 2I/Borisov, two interstellar objects.

More information Designation, a (AU) ...

See also

Notes

  1. The Jupiter Tisserand invariant or Tisserand's parameter with respect to Jupiter can be derived from Jupiter's semi-major axis (aJ) and the minor planet's orbital elements (a, e and i) as follows:[lower-alpha 2]
    aJ/a + 2(cosi) × a/aJ × (1-e2)
    Note
    In order to agree with the data displayed at the JPL Small-Body Database from which the orbital elements are sourced,[lower-alpha 3] the calculation of the Tisserand invariant uses a value of 5.203363 AU for Jupiter's osculating semi-major axis (aJ). Also, the degrees of the objects inclination need to be converted into the radian equivalent such as in:
    ($a_j / $a) + (2 * cos(deg2rad($i))) * sqrt(($a/$a_j) * (1 - $e * $e)).

References

  1. Jewitt, David (August 2013). "The DAMOCLOIDS". UCLA, Department of Earth and Space Sciences. Retrieved 14 February 2014. (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 13 February 2011.
  4. "JPL Small-Body Database Search Engine: asteroids and T-Jupiter <= 2". JPL Solar System Dynamics. Retrieved 3 July 2021. Search parameters used: Limited by object type/group: Asteroids and T-Jupiter <= 2
  5. "NEO Close-Approaches (Between 1900 and 2200)". NASA/JPL Near-Earth Object Program. Archived from the original on 13 December 2012. Retrieved 22 June 2012. (sorted by descending relative velocity, dist<0.5AU = "215,221 close-Earth approaches")
  6. "List Of Other Unusual Objects". Minor Planet Center. Retrieved 1 June 2019.
  7. "JPL Small-Body Orbital Elements – ASCII Files". JPL Solar System Dynamics. Retrieved 16 June 2021.

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