Cometary Science Newsletter

April 2020
Michael S. P. Kelley (

Refereed Articles

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

Potential Themis Family Asteroid Contribution to the Jupiter-Family Comet Population

  • Hsieh, H. H. 1,2
  • Novaković, B. 3
  • Walsh, K. J. 4
  • Schörghofer, N. 1
  1. Planetary Science Institute
  2. Academia Sinica, Institute of Astronomy and Astrophysics
  3. University of Belgrade
  4. Southwest Research Institute

Recent dynamical analyses suggest that some Jupiter family comets (JFCs) may originate in the main asteroid belt instead of the outer solar system. This possibility is particularly interesting given evidence that icy main-belt objects are known to be present in the Themis asteroid family. We report results from dynamical analyses specifically investigating the possibility that icy Themis family members could contribute to the observed population of JFCs. Numerical integrations show that such dynamical evolution is indeed possible via a combination of eccentricity excitation apparently driven by the nearby 2:1 mean-motion resonance with Jupiter, gravitational interactions with planets other than Jupiter, and the Yarkovsky effect. We estimate that, at any given time, there may be tens of objects from the Themis family on JFC-like orbits with the potential to mimic active JFCs from the outer solar system, although not all, or even any, may necessarily be observably active. We find that dynamically evolved Themis family objects on JFC-like orbits have semimajor axes between 3.15 au and 3.40 au for the vast majority of their time on such orbits, consistent with the strong role that the 2:1 mean-motion resonance with Jupiter likely plays in their dynamical evolution. We conclude that a contribution from the Themis family to the active JFC population is plausible, although further work is needed to better characterize this contribution.

The Astronomical Journal (Published)

DOI: 10.3847/1538-3881/ab7899 NASA ADS: 2020arXiv200209008H arXiv: 2002.09008

CO Gas and Dust Outbursts from Centaur 29P/Schwassmann–Wachmann

  • Wierzchos, K.1
  • Womack, M.2
  1. Catalina Sky Survey, Lunar and Planetary Lab.
  2. Florida Space Institute, University of Central Florida.

29P/Schwassmann–Wachmann is an unusual solar system object. Originally classified as a short-period comet, it is now known as a Centaur that recently transferred to its current orbit, and may become a Jupiter family comet. It has exhibited a dust coma for over 90 yr, and regularly undergoes significant dust outbursts. Carbon monoxide is routinely detected in high amounts and is typically assumed to play a large role in generating the quiescent dust coma and outbursts. To test this hypothesis, we completed two three-month-long observing campaigns of the CO J = 2–1 rotational line using the Arizona Radio Observatory 10 m Submillimeter Telescope during 2016 and 2018–2019, and compared the results to visible magnitudes obtained at the same time. As the Centaur approached its 2019 perihelion, the quiescent dust coma grew ~45% in brightness, while it is unclear whether the quiescent CO production rate also increased. A doubling of the CO production rate on 2016 February 28.6 UT did not trigger an outburst nor a rise in dust production for at least 10 days. Similarly, two dust outbursts occurred in 2018 while CO production continued at quiescent rates. Two other dust outbursts may show gas involvement. The data indicate that CO and dust outbursts are not always well correlated. This may be explained if CO is not always substantially incorporated with the dust component in the nucleus, or if CO is primarily released through a porous material. Additionally, other minor volatiles or physical processes may help generate dust outbursts.

The Astronomical Journal (Published)

DOI: 10.3847/1538-3881/ab6e68 arXiv: 2001.09537