Evidence for Physical Aging of Periodic Comets

Abstract

ABSTRACT. Observational evidence for the aging processes in periodic comets is reviewed. This includes progressive changes of the comets' absolute brightness, sudden destructive events (outbursts and splitting of cometary nuclei), temporary intermissions in activity, total disappearance, and existence of asteroidal objects moving in cometary orbits. Indirect statistical evidence is provided by the equilibrium between the aging rate and the net injection of comets into the inner planetary system. All of this information is consistent with typical active lifetimes of 200 to 500 revolutions at small perihelion distances (q < 3 AU). The active lifetimes are sometimes intermitted by dormant periods, which tend to occur especially during the latest phases of evolution. Splits and outbursts do not seem to have a decisive statistical effect on the survival time. Some periodic comets evolve into inactive asteroid-like objects, but the question of whether these still contain some supply of volatiles, and thus can renew their activity, remains open.

The Contribution of Dwarf Planets to the Origin of Jupiter Family Comets

“…where a J is Jupiter's semimajor axis, and a, e, and i are the semimajor axis, eccentricity, and inclination of the particle. It has been shown that T J is a suitable parameter to differentiate between the Jupiter Family and Halley-type comets, both of which are considered SPCs (historically, those with period below 200 yr; the JFCs having periods below 20 yr); however, by only considering the period as a classifying criteria, one ends with a large overlap between both families, thus a dynamically motivated criterion such as T J turns out to be a better choice in defining families among the observed comets, with Halley-types having a T J < 2 (Kresák 1972). In Fig.…”

Nucleus of active asteroid 358P/Pan-STARRS (P/2012 T1)

“…Active asteroids have orbits typical of asteroids (with a Tisserand parameter relative to Jupiter >3, Kresák 1972), but temporarily display dust activity similar to comets (Hsieh & Jewitt 2006;Jewitt 2012;Jewitt et al 2015b). While cometary activity is generally thought to be driven by the sublimation of embedded volatiles (Whipple 1950), the situation is likely more diverse in asteroids.…”