Cometary Science Newsletter

March 2018
Michael S. P. Kelley (

Refereed Articles

Abstracts of articles in press or recently published. Limited to 3000 characters.

Triggering the Activation of Main Belt Comets: The Effect of Porosity

  • Haghighipour, N. 1
  • Maindl, T. I. 2
  • Schaefer C. M. 3
  • Wandel, O. J. 3
  1. Institute for Astronomy, University of Hawaii-Manoa
  2. Department of Astrophysics, University of Vienna, Austria
  3. Institute for Astronomy and Astrophysics, University of Tuebingen, Germany

It has been suggested that the comet-like activity of Main Belt Comets is due to the sublimation of sub-surface water-ice that is exposed when these objects are impacted by meter-sized bodies. We recently examined this scenario and showed that such impacts can in fact excavate ice and present a plausible mechanism for triggering the activation of MBCs (Haghighipour et al. 2016). However, because the purpose of that study was to prove the concept and identify the most viable ice-longevity model, the porosity of the object and the loss of ice due to the heat of impact were ignored. In this paper, we extend our impact simulations to porous materials and account for the loss of ice due to an impact. We show that for a porous MBC, impact craters are deeper, reaching to approximately 15 m implying that if the activation of MBCs is due to the sublimation of sub-surface ice, this ice has to be within the top 15 m of the object. Results also indicate that the loss of ice due to the heat of impact is negligible, and the re-accretion of ejected ice is small. The latter suggests that the activities of current MBCs are most probably from multiple impact sites. Our study also indicates that in order for sublimation from multiple sites to account for the observed activity of the currently known MBCs, the water content of MBCs (and their parent asteroids) needs to be larger than the values traditionally considered in models of terrestrial planet formation.

Astrophysical Journal (Published)

DOI: 10.3847/1538-4357/aaa7f3 NASA ADS: 2018ApJ...855...60H arXiv: 1801.08247

Finding Long Lost Lexell's Comet: The Fate of the First Discovered Near-Earth Object

  • Ye, Q.-Z.1
  • Wiegert, P. A.2
  • Hui, M.-T. 3
  1. Caltech/IPAC
  2. University of Western Ontario
  3. UCLA

Jupiter-family Comet D/1770 L1 (Lexell) was the first discovered Near-Earth Object (NEO), and passed the Earth on 1770 Jul 1 at a recorded distance of 0.015 au. The comet was subsequently lost due to unfavorable observing circumstances during its next apparition followed by a close encounter with Jupiter in 1779. Since then, the fate of D/Lexell has attracted interest from the scientific community, and now we revisit this long-standing question. We investigate the dynamical evolution of D/Lexell based on a set of orbits recalculated using the observations made by Charles Messier, the comet's discoverer, and find that there is a 98% chance that D/Lexell remains in the Solar System by the year of 2000. This finding remains valid even if a moderate non-gravitational effect is imposed. Messier's observations also suggest that the comet is one of the largest known near-Earth comets, with a nucleus of ≳10 km in diameter. This implies that the comet should have been detected by contemporary NEO surveys regardless of its activity level if it has remained in the inner Solar System. We identify asteroid 2010 JL33 as a possible descendant of D/Lexell, with a 0.8% probability of chance alignment, but a direct orbital linkage of the two bodies has not been successfully accomplished. We also use the recalculated orbit to investigate the meteors potentially originating from D/Lexell. While no associated meteors have been unambiguously detected, we show that meteor observations can be used to better constrain the orbit of D/Lexell despite the comet being long lost.

Astronomical Journal (In press)

arXiv: 1802.08904