Cometary Science Newsletter

February 2017
Michael S. P. Kelley (

Refereed Articles

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

Non-Gravitational Acceleration of the Active Asteroids

  • Hui, Man-To 1
  • Jewitt, David 1,2
  1. Department of Earth, Planetary, and Space Sciences, UCLA
  2. Department of Physics and Astronomy, UCLA

Comets can exhibit non-gravitational accelerations caused by recoil forces due to anisotropic mass loss. So might active asteroids. We present an astrometric investigation of 18 active asteroids in search of non-gravitational acceleration. Statistically significant (signal-to-noise ratio (SNR) > 3) detections are obtained in three objects: 313P/Gibbs, 324P/La Sagra and (3200) Phaethon. The strongest and most convincing detection (>7σ in each of three orthogonal components of the acceleration), is for the ~1 km diameter nucleus of 324P/La Sagra. A 4.5σ detection of the transverse component of the acceleration of 313P/Gibbs (also ~1 km in diameter) is likely genuine too, as evidenced by the stability of the solution to the rejection or inclusion of specific astrometric datasets. We also find a 3.4σ radial-component detection for ~5 km diameter (3200) Phaethon, but this detection is more sensitive to the inclusion of specific datasets, suggesting that it is likely spurious in origin. The other 15 active asteroids in our sample all show non-gravitational accelerations consistent with zero. We explore different physical mechanisms which may give rise to the observed non-gravitational effects, and estimate mass-loss rates from the non-gravitational accelerations. We present a revised momentum-transfer law based on a physically realistic sublimation model for future work on non-gravitational forces, but note that it has little effect on the derived orbital elements.

The Astronomical Journal (In press)

arXiv: 1612.06920

Modeling the Nearly Isotropic Comet Population in Anticipation of LSST Observations

  • Silsbee, Kedron 1
  • Tremaine, Scott 2
  1. Department of Astrophysical Sciences, Princeton University
  2. Institute for Advanced Study, Princeton, NJ

We run simulations to determine the expected distribution of orbital elements of nearly isotropic comets (NICs) in the outer solar system, assuming that these comets originate in the Oort Cloud at thousands of au and are perturbed into the planetary region by the Galactic tide. We show that the Large Synoptic Survey Telescope (LSST) should detect and characterize the orbits of hundreds to thousands of NICs with perihelion distance outside 5 au. Observing NICs in the outer solar system is our only way of directly detecting comets from the inner Oort Cloud, as these comets are dynamically excluded from the inner solar system by the giant planets. Thus the distribution of orbital elements constrains the spatial distribution of comets in the Oort cloud and the environment in which the solar system formed. Additionally, comet orbits can be characterized more precisely when they are seen far from the Sun as they have not been affected by non-gravitational forces.

The Astronomical Journal (Published)

DOI: 10.3847/0004-6256/152/4/103 NASA ADS: 2016AJ....152..103S arXiv: 1607.07882

Modelling the evolution of a comet subsurface: implications for 67P/Churyumov-Gerasimenko

  • Guilbert-Lepoutre, Aurélie 1
  • Rosenberg, Eric D. 2
  • Prialnik, Dina 2
  • Besse, Sébastien 3
  1. CNRS/UTINAM, Univ. Franche Comté, Besancon, France
  2. Department of Geosciences, Tel-Aviv University, Tel-Aviv, Israel
  3. ESA/ESAC, Madrid, Spain

Modelling the evolution of comets is a complex task aiming at providing constraints on physical processes and internal properties that are inaccessible to observations, although they could potentially bring key elements to our understanding of the origins of these primitive objects. This field has made a tremendous step forward in the post-Giotto area, owing to detailed space- and ground-based observations, as well as detailed laboratory simulations of comet nuclei. In this paper, we review studies that we believe are significant for interpreting the observations of 67P/Churyumov–Gerasimenko by the ESA/Rosetta mission, and provide new calculations where needed. These studies hold a strong statistical significance, which is exactly what is needed for this comet with an orbital evolution that cannot be traced back accurately for more than hundreds of years. We show that radial and lateral differentiation may have occurred on 67P’s chaotic path to the inner Solar system, and that internal inhomogeneities may result in an erratic activity pattern. Finally, we discuss the origins of circular depressions seen on several comets including 67P, and suggest that they could be considered as evidence of the past processing of subsurface layers.

Monthly Notices of the Royal Astronomical Society (Published)

DOI: 10.1093/mnras/stw2371 NASA ADS: 2016MNRAS.462S.146G