Cometary Science Newsletter

August 2020
Michael S. P. Kelley (

Refereed Articles

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

Photometry and high-resolution spectroscopy of comet 21P/Giacobini-Zinner during its 2018 apparition

  • Y. Moulane1, 2, 3
  • E. Jehin2
  • P. Rousselot4
  • J. Manfroid2
  • Y. Shinnaka5
  • F. J. Pozuelos2
  • D. Hutsemékers2
  • C. Opitom1, 6
  • B. Yang1
  • and Z. Benkhaldoun3
  1. European Southern Observatory, Alonso de Cordova 3107, Vitacura, Santiago, Chile
  2. Space sciences, Technologies & Astrophysics Research (STAR) Institute, University of Liège, Liège, Belgium
  3. Oukaimeden Observatory, High Energy Physics and Astrophysics Laboratory, Cadi Ayyad University, Marrakech, Morocco
  4. Institut UTINAM UMR 6213, CNRS, Univ. Bourgogne Franche-Comté, OSU THETA, BP 1615, 25010 Besançon Cedex, France
  5. Koyama Astronomical Observatory, Kyoto Sangyo University, Motoyama, Kamigamo, Kita-ku, Kyoto 603-8555, Japan
  6. Institute for Astronomy, University of Edinburgh, Royal Observatory, Edinburgh EH9 3HJ, UK

We report on photometry and high resolution spectroscopy of the chemically peculiar Jupiter-family Comet (hereafter JFC) 21P/Giacobini-Zinner. Comet 21P is a well known member of the carbon-chain depleted family but displays also a depletion of amines. We monitored continuously the comet over more than seven months with the two TRAPPIST telescopes (TN and TS), covering a large heliocentric distance range from 1.60 au inbound to 2.10 au outbound with a perihelion at 1.01 au on September 10, 2018. We computed and followed the evolution of the dust (represented by Afρ) and gas production rates of the daughter species OH, NH, CN, C3, and C2 and their relative abundances to OH and to CN over the comet orbit. We compared them to those measured in the previous apparitions. The activity of the comet and its water production rate reached a maximum of (3.72±0.07)×1028 molec/s on August 17, 2018 (rh=1.07 au), 24 days before perihelion. The peak value of A(0)fρ was reached on the same date (1646±13) cm in the red filter. The abundance ratios of the various species are remarkably constant over a large range of heliocentric distances, before and after perihelion, showing a high level of homogeneity of the ices in the surface of the nucleus. The behaviour and level of the activity of the comet is also remarkably similar over the last five orbits. About the coma dust colour, 21P shows reflectively gradients similar to JFCs. We obtained a high resolution spectrum of 21P with UVES at ESO VLT one week after perihelion. Using the CN B-X (0,0) violet band, we measured 12C/13C and 14N/15N isotopic ratios of 100±10 and 145±10, respectively, both in very good agreement with what is usually found in comets.

Astronomy and Astrophysics (Published)

DOI: 10.1051/0004-6361/202037997

Broadband photometry of asteroid 6478 Gault: activity and morphology

  • Borysenko, S. 1
  • Baransky, A. 2
  • Simon, A 3
  • Vasylenko, A 3
  1. Main Astronomical Observatory of NAS of Ukraine, Ukraine
  2. Astronomical Observatory of Taras Shevchenko National University of Kyiv, Ukraine
  3. Taras Shevchenko National University of Kyiv, Ukraine

We present the results of a short observational program of asteroid 6478 Gault using of V and R Johnson filters realized at the Kyiv Comet Station during January to April 2019. Color indices and distribution of brightness in the comet‐like tail were calculated. We conducted a comparative analysis of circumstances of the asteroid 6478 Gault activity with others morphologically similar active main‐belt asteroids.

Astronomische Nachrichten (Published)

DOI: 10.1002/asna.202013699 arXiv: 2005.07270

Evolution of orbits about comets with arbitrary comae

  • Moretto, M. 1
  • McMahon, J. 1
  1. University of Colorado Boulder

Spacecraft and natural objects orbiting an active comet are perturbed by gas drag from the coma. These gases expand radially at about 0.5 km/s, much faster than orbital velocities that are on the order of meters per second. The coma has complex gas distributions and is difficult to model. Accelerations from gas drag can be on the same order of gravity and are currently poorly understood. Semi-analytical solutions for the evolution of the Keplerian orbital elements of a spacecraft orbiting a comet using simplified drag and coma models are derived using a Fourier series expansion in the argument of latitude. It is found that the mean element evolution is only dependent on the zeroth- and first-order terms of the Fourier series expansion. For an arbitrary, inverse-square, radial, perturbing force, there are no frozen orbits; however, the argument of pericenter has a stable equilibrium and an unstable equilibrium and the angular momentum vector of the orbit is constant. Furthermore, the radius of the orbit at two specific angles relative to the ascending node is preserved. The evolution of the orbit is governed by the argument of pericenter, resulting in orientations that raise and lower the radius of pericenter and implying safe and unsafe orbit orientations for spacecraft operations.

Celestial Mechanics and Dynamical Astronomy (Published)

DOI: 10.1007/s10569-020-09973-5