Dormant comets in the NEO population

Quan-Zhi Ye bio photo By Quan-Zhi Ye

In a Nutshell

Ye et al. (2016), MNRAS, 462, 3511

Comets have tails because they have volatile material such as water ice. When comets get close to the Sun, their water ice sublimate and bring dust into space, forming the tails. Once comets use up their water ice, they become dead and behave like asteroids (no tail). For years, people have been wondering how many such “dead comets” exist in the near-Earth region. Since dead comets behave like asteroids, it is difficult to find them.

However, the ejected dust may find its way to the Earth, becoming a “shooting star”, or a meteor. It is possible for us to detect the dust ejected by its parent comet bfore the comet died, though careful calculation is needed to ensure the meteor is indeed from the now-dead comet.

We searched among the 13 milion meteors detected by the Canadian Meteor Orbit Radar. We concluded that about 2% of the near-Earth asteroids are dead comets. This number is lower than theoretical predictions, and we are still trying to understand why.

Abstract

Dormant comets in the near-Earth object (NEO) population are thought to be involved in the terrestrial accretion of water and organic materials. Identification of dormant comets is difficult as they are observationally indistinguishable from their asteroidal counterparts, however, they may have produced dust during their final active stages which potentially are detectable today as weak meteor showers at the Earth. Here we present the result of a reconnaissance survey looking for dormant comets using 13 567 542 meteor orbits measured by the Canadian Meteor Orbit Radar (CMOR). We simulate the dynamical evolution of the hypothetical meteoroid streams originated from 407 near-Earth asteroids in cometary orbits that resemble orbital characteristics of Jupiter-family comets (JFCs). Out of the 44 hypothetical showers that are predicted to be detectable by CMOR, we identify five positive detections that are statistically unlikely to be chance associations, including three previously known associations. This translates to a lower limit to the dormant comet fraction of 2.0 +/- 1.7 per cent in the NEO population and a dormancy rate of ~10^-5 per year per comet. The low dormancy rate confirms disruption and dynamical removal as the dominant end state for near-Earth JFCs. We also predict the existence of a significant number of meteoroid streams whose parents have already been disrupted or dynamically removed.

Favorite Figure

fig-ev-wc

Meteor activity from four confirmed dead comets. The arrows mark the time of predicted meteor activity, with the assumption that the parent body was an active comet (if the parent body has not been an active comet, no meteor should be observed). It can be seen that each arrow corresponds to an increase in meteor activity, supporting the assumption that each parent body has been active in the past.