PSJC #166 Apriil 18 2014

Javier Licandro (IAC)

Are Comets the Asteroids in Cometary Orbits?

Asteroids in cometary orbits (ACOs) are objects in typical cometary orbits that never showed any kind of activity. Comets might develop an asteroidal appearance when sublimation stops, either due to the depletion of volatile materials (dead or extinct comets) or by the growth of a surface crust of refractory material up to a thickness that prevents subsurface volatiles from warming up to sublimation temperature (dormant comets). The study of ACOs is very important to understand the formation of cometary dust mantles and the end states of comets, in order to determine the population of Jupiter family comets (JFCs), and to understand the dynamical processes that move asteroids from typical asteroidal orbits to cometary-like ones.

Tancredi (2014) presents a much more restrictive criterion to identify ACOs than those used in previous papers that ensures that the objects have a dynamical evolution similar to the population of periodic comets. Tancredi's criterion is based on the Tisserand parameter and the Minimum Orbital Intersection Distance (MOID), and considers some information regarding the aphelion and perihelion distances and eliminates objects in mean-motion resonances. After applying a filter to the sample of over half a million asteroids already discovered to select the precise orbits, Tancredi (2014) apply the proposed classification criterion to identify the ACOs. The resulting sample consists of 244 ACOs that are further classified in subclasses similar to the cometary classification: 188 objects belong to the Jupiter Family group and 56 objects have Halley Type Orbits (also known as Damocloids ). These are the best known extinct/dormant comets candidates from a dynamical point of view.

In this presentation I will review the known spectral, diameter, beaming parameter (η), and albedo properties of the objects in Tancredi's list based on already published data and the analysis of WISE observations. I will compare the spectral, size, η, and albedo distribution with that of comets and other primitive asteroids and show that they are very similar, which support the cometary nature of ACOs.