What is "damocloid"

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 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 T ≤ 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 , , and .

Using the Tisserand parameter (T-Jupiter ≤ 2) there are currently 96 damocloid candidates. Of these objects, 74 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. Other damocloids include: , , , , and 20461 Dioretsa.

Retrograde objects such as Halley's Comet and damocloid can have relative velocities to Earth of .