Cometary Science Newsletter

December 2022
Michael S. P. Kelley (

Conference Announcements

Announcements for cometary conferences or workshops. Limited to 2000 characters.

Comet Community Chat

Invitation: Since January 2022, every month on the last Friday of the month at 4-6:30 pm, members of the cometary scientific community having been getting together socially via zoom to discuss the latest happenings in the field. New comet observations and scientific discoveries, recent visits to the telescope, job changes and openings are all fair game, as are older shared stories of colleagues and comet lore. Started in response to the social isolation imparted by COVID quarantining so that we would see each other more than once a year for 2 hours at the virtual DPS meeting, we have now gotten together 8 times since January. Recent discussions have included JWST observing plans, giant comet UN271, what makes a comet great, and distant comet activity trends. All interested parties are welcome, especially early career scientists with new research results to relate. If you are not already on the 140+ person email distribution list and would like to participate, please send an email request to asking to be included.

Refereed Articles

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

Thermal Alteration and Differential Sublimation Can Create Phaethon’s “Rock Comet” Activity and Blue Color

  • Lisse, C.M.1
  • Steckloff, J.K.2,3
  1. Johns Hopkins University Applied Physics Laboratory
  2. Planetary Science Institute
  3. University of Texas at Austin

In 2010 Jewitt and Li published a paper examining the behavior of “comet-asteroid transition object” 3200 Phaethon, arguing it was asteroid-like in its behavior throughout most of its orbit, but that near its perihelion, at a distance of only 0.165 AU from the sun, its dayside temperatures would be hot enough to vaporize rock (>1000 K, Hanus et al. 2016). Thus it would act like a “rock comet” as gases produced from evaporating rock were released from the body, in a manner similar to the more familiar sublimation of water ice into vacuum seen for comets coming within ~3 AU of the Sun. In this Note we predict that the same thermal effects that would create "rock comet" behavior with Qgas ~ 10^22 mol/sec at perihelion have also helped to greatly bluen Phaethon’s surface via preferential thermal alteration and sublimative removal of Fe and refractory organics, known reddening and darkening agents. These predictions are testable by searching for signs of spectral bluening of the surfaces of other small bodies in Phaethon-like small perihelion orbits, including comets, and by in situ measurements of Phaethon’s surface and coma composition near perihelion with the upcoming DESTINY+ mission (Kawakatsu & Itawa 2013, Arai et al. 2018) to Phaethon by JAXA.

Icarus (Published)

DOI: 10.1016/j.icarus.2022.114995 NASA ADS: 2022Icar..38114995L arXiv: 2203.09876

29P/Schwassmann-Wachmann 1: A Rosetta Stone for Amorphous Water Ice and CO <-> CO2 Conversion in Centaurs and Comets?

  • C.M. Lisse 1
  • J.K. Steckloff 2,3
  • D. Prialnik 4
  • M. Womack 5,6
  • O. Harrington Pinto 5
  • G. Sarid 7
  • Y.R. Fernandez 5,8
  • C.A. Schambeau 5,8
  • T. Kareta 9
  • N.H. Samarasinha 2
  • W. Harris 10
  • K. Volk 10
  • L.M. Woodney 11
  • D.P. Cruikshank 5
  • S.A. Sandford 12
  1. Johns Hopkins University Applied Physics Laboratory
  2. Planetary Science Institute
  3. University of Texas at Austin
  4. Tel Aviv University
  5. University of Central Florida
  6. National Science Foundation
  7. SETI Institute
  8. Florida Space Institute
  9. Lowell Observatory
  10. Lunar & Planetary Laboratory, University of Arizona
  11. Cal State University San Bernardino
  12. NASA/Ames Research Center

Centaur 29P/Schwassmann-Wachmann 1 (SW1) is a highly active object orbiting in the transitional “Gateway” region between the Centaur and Jupiter Family Comet regions. SW1 is unique among the Centaurs in that it experiences quasi-regular major outbursts and produces CO emission continuously; however, the source of the CO is unclear. We argue that due to its very large size (~32 km radius), SW1 is likely still responding, via amorphous water ice (AWI) conversion to crystalline water ice (CWI), to the “sudden” change in its external thermal environment produced by its dynamical migration from the Kuiper belt to the Gateway Region at the inner edge of the Centaur region at 6 au. It is this conversion process that is the source of the abundant CO and dust released from the object during its quiescent and outburst phases. If correct, these arguments have a number of important predictions testable via remote sensing and in situ spacecraft characterization, including: the quick release on Myr timescales of CO from AWI conversion for any few km-scale scattered disk KBO transiting into the inner system; that to date SW1 has only converted between 50 to 65% of its nuclear AWI to CWI; that volume changes upon AWI conversion could have caused subsidence and cave-ins, but not significant mass wasting or crater loss; that SW1’s coma should contain abundant amounts of CWI CO2-rich “dust” particles; and that when SW1 transits into the inner system within the next 10,000 years, it will be a very different kind of JFC comet.

Planetary Science Journal (Published)

DOI: 10.3847/PSJ/ac9468 NASA ADS: 2022arXiv220909136L arXiv: arXiv:2209.09136

C/2020 S3 (Erasmus): Comet with a presumably transient maximum of linear polarization Pmax

  • Chornaya, E. 1
  • Zubko, E. 2
  • Kochergin, A. 1
  • Zheltobryukhov, M. 1
  • Videen, G. 2.3
  • Kornienko, G. 1
  • Kim, S.S. 2,4
  1. The Ussuriysk Astrophysical Observatory, Institute of Applied Astronomy of RAS
  2. Humanitas College , Kyung Hee University
  3. Center for Polarimetric Remote Sensing, Space Science Institute
  4. Department of Astronomy and Space Science, Kyung Hee University

We measured the degree of linear polarization of Comet C/2020 S3 (Erasmus) on November 13, 20, 22, and 23, 2020, while the comet was observed at large phase angles, α = 62.6° – 66.6°. On the first two epochs, the polarization closely matched what was previously observed in Comet C/1989 X1 (Austin). On the third epoch, the polarization was found to rise slightly, and on the latest epoch, it rose significantly, exceeding that of Comet Austin. On the last observation, the polarization of Comet Erasmus appears to be more consistent with what was previously seen in Comet C/1996 B2 (Hyakutake) at a similar phase angle. While such short-term transient behavior has been seen previously, Comets Austin and Hyakutake belong to two different classes in classifications based on the amplitude of their positive polarization Pmax and, hence, Comet Erasmus revealed a transition from the class of low-Pmax comets to that of high-Pmax comets within only a few days. Polarization images and modeling suggest that the transition occurred due to a decrease in the relative abundance of Mg-rich silicate particles in the inner coma by 1/3, revealing a qualitative change in emanations of dust particles from the Erasmus nucleus.

Monthly Notices of the Royal Astronomical Society (Published)

DOI: 10.1093/mnras/stac3201 NASA ADS: 2022MNRAS.tmp.2986C

Color variations of comet 29P/Schwassmann-Wachmann 1 in 2018

  • Voitko, A. 1
  • Zubko, E. 2
  • Ivanova, O. 1,3,4
  • Luk’yanyk, I. 4
  • Kochergin, A. 2
  • Husárik, M. 1
  • Videen, G. 5
  1. Astronomical Institute of the Slovak Academy of Sciences
  2. Humanitas College, Kyung Hee University
  3. Main Astronomical Observatory of National Academy of Sciences
  4. Astronomical Observatory, Taras Shevchenko National University of Kyiv
  5. Space Science Institute

We measure the photometric color in the inner coma of Comet 29P/Schwassmann–Wachmann 1 on nine nights in August and October, 2018. We see variations in the color slope from 𝑆′ =(19.72 ±1.72)% per 0.1 μm to 𝑆′ =–(6.88 ±1.72)% per 0.1 μm. The blue color is accompanied with increasing brightness suggesting that it is caused by mild outburst activity. We model the extreme values of 𝑆′ using agglomerated debris particles. The reddest color suggests a coma dominated by Fe–Mg silicate particles or organic particles obeying a differential power-law size distribution with power index 𝑛 ≈2.6 ±0.3. The bluest color is indicative of a high abundance of either water–ice having a power index 𝑛 ≤2 or Mg-rich silicate particles having 𝑛 ≈2.5 ±0.3. From these properties we compute an instantaneous dustload of the inner coma ranging from as low as 1450 ± 150 m^3 when there was sporadic activity to 5,900—26,300 m^3 when there was mild activity. Such a dustload is one-two orders of magnitude larger compared to other comets. We perform simulation of the dust motion within the coma to estimate the number of particles leaving our aperture to constrain the dust production rate. We find a dust production rate of 𝑄dust ≈4.6 ±2.3 kg/s during the quiescent period, and 𝑄dust ≈17.6 ±2.8 kg/s during a mild outburst. Such values appear at the lower limit of what has been calculated previously.

Icarus (Published)

DOI: 10.1016/j.icarus.2022.115236