Cometary Science Newsletter

November 2021
Michael S. P. Kelley (

Refereed Articles

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

Physical Characterization of Main-Belt Comet (248370) 2005 QN173

  • Henry H. Hsieh 1,2
  • Colin O. Chandler 3
  • Larry Denneau 4
  • Alan Fitzsimmons 5
  • Nicolas Erasmus 6
  • Michael S. P. Kelley 7
  • Matthew M. Knight 8,7
  • Tim A. Lister 9
  • Jana Pittichová 10
  • Scott S. Sheppard 11
  • Audrey Thirouin 12
  • Chadwick A. Trujillo 3
  • Helen Usher 13
  • Edward Gomez 14
  • Joey Chatelain 9
  • Sarah Greenstreet 15,16
  • Tony Angel 17
  • Richard Miles 18
  • Paul Roche 19
  • Ben Wooding 20
  1. Planetary Science Institute, Tucson, Arizona, USA
  2. Academia Sinica Institute of Astronomy and Astrophysics, Taipei, Taiwan
  3. Northern Arizona University, Flagstaff, Arizona, USA
  4. University of Hawaii, Honolulu, Hawaii, USA
  5. Queen's University, Belfast, United Kingdom
  6. South African Astronomical Observatory, Cape Town, South Africa
  7. University of Maryland, College Park, Maryland, USA
  8. United States Naval Academy, Annapolis, Maryland, USA
  9. Las Cumbres Observatory, Goleta, California, USA
  10. Jet Propulsion Laboratory, Pasadena, California, USA
  11. Carnegie Institution for Science, Washington, D.C., USA
  12. Lowell Observatory, Flagstaff, Arizona, USA
  13. The Open University, Milton Keynes, United Kingdom
  14. Las Cumbres Observatory, Cardiff, United Kingdom
  15. Asteroid Institute, Mill Valley, California, USA
  16. University of Washington, Seattle, Washington, USA
  17. Harlingten Observatory, Granada, Spain
  18. British Astronomical Association, United Kingdom
  19. Faulkes Telescope Project, Cardiff, United Kingdom
  20. St. Mary's Catholic Primary School, Bridgend, United Kingdom

We report results from new and archival observations of the newly discovered active asteroid (248370) 2005 QN137, which has been determined to be a likely main-belt comet based on a subsequent discovery that it is recurrently active near perihelion. From archival data analysis, we estimate g'-, r'-, i'-, and z'-band absolute magnitudes for the nucleus of Hg=16.62±0.13, Hr=16.12±0.10, Hi=16.05±0.11, and Hz=15.93±0.08, corresponding to nucleus colors of g'-r'=0.50±0.16, r'-i'=0.07±0.15, and i'-z'=0.12±0.14, an equivalent V-band absolute magnitude of HV=16.32±0.08, and a nucleus radius of rn=1.6±0.2 km (using a V-band albedo of pV=0.054±0.012). Meanwhile, we find mean near-nucleus coma colors when 248370 was active of g'-r'=0.47±0.03, r'-i'=0.10±0.04, and i'-z'=0.05±0.05, and similar mean dust tail colors, suggesting that no significant gas coma is present. We find approximate ratios between the scattering cross-sections of near-nucleus dust (within 5000 km of the nucleus) and the nucleus of Ad/An=0.7±0.3 on 2016 July 22, and 1.8 < Ad/An < 2.9 in 2021 July and August. During the 2021 observation period, the coma declined in intrinsic brightness by ~0.35 mag (or ~25%) in 37 days, while the surface brightness of the dust tail remained effectively constant over the same period. Constraints derived from the sunward extent of the coma suggest that terminal velocities of ejected dust grains are extremely slow (~1 m/s for 1 micron particles), indicating that the observed dust emission may have been aided by rapid rotation of the nucleus lowering the effective escape velocity.

Astrophysical Journal Letters (In press)

NASA ADS: 2021arXiv210914822H arXiv: 2109.14822

VLT spectropolarimetry of comet 67P: Dust environment around the end of its intense Southern summer

  • Yuna G. Kwon 1
  • Stefano Bagnulo 2
  • Johannes Markkanen 1,3
  • Jessica Agarwal 1,3
  • Ludmilla Kolokolova 4
  • Anny-Chantal Levasseur-Regourd 5
  • Colin Snodgrass 6
  • Gian P. Tozzi 7
  1. Technische Universität Braunschweig, Germany
  2. Armagh Observatory, UK
  3. Max Planck Institute for Solar System Research, Germany
  4. University of Maryland, USA
  5. LATMOS Sorbonne Université, France
  6. University of Edinburgh, UK
  7. INAF, Italy

We report our new spectropolarimetric observations for 67P dust over 4,000–9,000 Å using the ESO/Very Large Telescope in January–March 2016 (phase angle ranging ∼26–5 deg) to constrain the properties of the dust particles of 67P and therefrom diagnose the dust environment of its coma and near-surface layer at around the end of the Southern summer of the comet. We examined the optical behaviours of the dust, which, together with Rosetta colour data, were used to search for dust evolution with cometocentric distance. Modelling was also conducted to identify the dust attributes compatible with the results. The spectral dependence of the polarisation degree of 67P dust is flatter than found in other dynamical groups of comets in similar observing geometry. The depth of its negative polarisation branch appears to be a bit shallower than in long-period comets and might be getting shallower as 67P repeats its apparitions. Its dust colour shows a change in slope around 5,500 Å, (17.3 ± 1.4) and (10.9 ± 0.6) % (1,000 Å)−1 for shortward and longward of the wavelength, respectively, which are slightly redder but broadly consistent with the average of Jupiter-Family comets. Observations of 67P dust in this study can be attributed to dust agglomerates of ∼100 μm in size detected by Rosetta in early 2016. A porosity of 60% shows the best match with our polarimetric results, yielding a dust density of ∼770 kg m−3. Compilation of Rosetta and our data indicates the dust's reddening with increasing nucleus distance, which may be driven by water-ice sublimation as the dust moves out of the nucleus. We estimate the possible volume fraction of water ice in the initially ejected dust as ∼6% (i.e. the refractory-to-ice volume ratio of ∼14).

Astronomy & Astrophysics (In press)

arXiv: 2110.00266

Some physical properties of a new Jupiter-family comet P/2019 LD2 (ATLAS) from broadband observations

  • Borysenko, S. 1
  • Kokhirova, G. 2
  • Rakhmatullaeva, F. 2
  1. Main Astronomical Observatory of NAS of Ukraine, Ukraine
  2. Institute of Astrophysics of NAS of Tajikistan, Tajikistan

New periodic comet P/2019 LD2 (ATLAS) located on unstable quasi-Trojan orbit still an interesting object to study in the last years. We present the results of broadband observations of comet P/2019 LD2 (ATLAS) performed at the Sanglokh observatory of the Institute of Astrophysics, National Academy of Sciences of Tajikistan for 5 nights in August 2020. The dependence of the Afρ parameters of the comet on the aperture radius is measured. We obtained the coma corrected upper limit of the cometary radius Rn ≤ 6.1 ± 0.1 km and calculated the absolute magnitude H0 = 11.41 ± 0.03. Finson – Probstein diagram method used to explain a dust tail appearance. A subgroup of comets with orbital parameters close to P/2019 LD2 (ATLAS) is analyzed.

Icarus (Published)

DOI: 10.1016/j.icarus.2021.114752

Leveraging the ALMA Atacama Compact Array for Cometary Science: An Interferometric Survey of Comet C/2015 ER61 (PanSTARRS) and Evidence for a Distributed Source of Carbon Monosulfide

  • Roth, N. X. 1,2
  • Milam, S. N. 1
  • Cordiner, M. A. 1,2
  • Bockelée-Morvan, D. 3
  • Biver, N. 3
  • Boissier, J. 4
  • Lis, D. C. 5
  • Remijan, A. J. 6
  • Charnley, S. B. 1
  1. Solar System Exploration Division, Astrochemistry Laboratory Code 691, NASA Goddard Space Flight Center, 8800 Greenbelt Rd, Greenbelt, MD 20771, USA
  2. Department of Physics, The Catholic University of America, 620 Michigan Ave., N.E. Washington, DC 20064, USA
  3. LESIA, Observatoire de Paris, Université PSL, CNRS, Sorbonne Université, Université de Paris, 5 place Jules Janssen, F-92195 Meudon, France
  4. Institut de Radioastronomie Millimetrique, 300 rue de la Piscine, F-38406 Saint Martin d'Heres, France
  5. Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109, USA
  6. National Radio Astronomy Observatory, 520 Edgemont Rd, Charlottesville, VA 22903, USA

We report the first survey of molecular emission from cometary volatiles using standalone Atacama Compact Array (ACA) observations from the Atacama Large Millimeter/Submillimeter Array (ALMA) toward comet C/2015 ER61 (PanSTARRS) carried out on UT 2017 April 11 and 15, shortly after its April 4 outburst. These measurements of HCN, CS, CH3OH, H2CO, and HNC (along with continuum emission from dust) probed the inner coma of C/2015 ER61, revealing asymmetric outgassing and discerning parent from daughter/distributed source species. This work presents spectrally integrated flux maps, autocorrelation spectra, production rates, and parent scale lengths for each molecule and a stringent upper limit for CO. HCN is consistent with direct nucleus release in C/2015 ER61, whereas CS, H2CO, HNC, and potentially CH3OH are associated with distributed sources in the coma. Adopting a Haser model, parent scale lengths determined for H2CO (Lp ~ 2200 km) and HNC (Lp ~ 3300 km) are consistent with previous work in comets, whereas significant extended source production (Lp ~ 2000 km) is indicated for CS, suggesting production from an unknown parent in the coma. The continuum presents a point-source distribution with a flux density implying an excessively large nucleus, inconsistent with other estimates of the nucleus size. It is best explained by the thermal emission of slowly moving outburst ejectas, with total mass 5–8 x 1010 kg. These results demonstrate the power of the ACA for revealing the abundances, spatial distributions, and locations of molecular production for volatiles in moderately bright comets such as C/2015 ER61.

The Astrophysical Journal (Published)

DOI: 10.3847/1538-4357/ac0441 arXiv: 2104.03210

Spitzer Space Telescope Spectroscopy of Comets

  • Kelley, M. S. P 1
  • Harker, D. E. 2
  • Woodward, C. E. 3
  • Wooden, D. H. 4
  1. University of Maryland
  2. University of California, San Diego
  3. University of Minnesota
  4. NASA Ames Research Center

We present spectra of comets observed with the Infrared Spectrograph (IRS) on the Spitzer Space Telescope. The observations are based on a select set of comets with high-quality data, reduced using a uniform approach. We summarize the observations, and detail our reduction methodology. Additional details on the calibration of cometary sources with the IRS instrument are also given, and plots of all spectra are included for reference.

The data set is publicly available at the Planetary Data System Small Bodies Node.

Planetary Data System (Published)