Cometary Science Newsletter

July 2018
Michael S. P. Kelley (

Comet Notes

Brief observational reports or other notes related to specific comets. Limited to 1000 characters. The CSN is not intended to replace telegram services or other breaking news outlets.

Comets 46P/Wirtanen and 21P/Giacobini-Zinner

In the June newsletter, we reported that Wirtanen had been recovered on May 8. It turns out that the object was actually a random asteroid (133655), that had nearly the same expected brightness and proper motion as Wirtanen, but was following ~77 arcsec behind the comet.

However, on June 18-20, Lori Feaga et al. (UMD) obtained observations of Wirtanen from the DCT. Astrometry from these observations, linked to measurements from 2014, confirming that it was indeed the comet and proving that the May object was not.

With the orbit computed from the June observations, Wirtanen was found in coadded frames from May 8, but with a brightness ~1.2 mag fainter than expected from pre-recovery observations. It is not yet clear how this will translate to the brightness around close approach to the Earth.

Additional information about these observations is included at the Wirtanen observing campaign website

Several new pages have been added to the campaign website, including:

  1. A compilation of observations of Comet Wirtanen that are available in public archives.
  2. A discussion of coma morphology and collaborations between the professional and amateur communities.
  3. A discussion of our tests of a proxy CN filter that we hoped would be useful to the amateur community. (Spoiler, we can't recommend it for the typical amateur, but high-level users may have facilities where it could be valuable).

Finally, we note that comet 21P/Giacobini-Zinner is getting brighter as it approaches its September perihelion. Although the Wirtanen campaign does not have extensive information about this comet, we are collecting information about observations that are planned or scheduled, so that others can use them for planning or proposing collaborative efforts. We ask that you submit information on your observations to the 21P/G-Z observation logs (under the "Other Campaign Objects" menu item).

Tony Farnham
for the Wirtanen Campaign

Refereed Articles

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

Dust modelling and a dynamical study of comet 41P/Tuttle-Giacobini-Kresak during its 2017 perihelion passage

  • Pozuelos, F.J. 1
  • Jehin, E. 1
  • Moulane, Y. 1,2
  • Opitom, C. 3
  • Manfroid, J. 1
  • Benkhaldoun, Z. 2
  • Gillon, M. 1
  1. Space sciences, Technologies and Astrophysics Research (STAR) Institute, Université de Liège, 19C Allée du 6 Août, B-4000 Liège, Belgium.
  2. Oukaimeden Observatory, High Energy Physics and Astrophysics Laboratory, Cadi Ayyad University, Marrakech, Morocco.
  3. European Southern Observatory, Alonso de Cordova 3107, Vitacura, Santiago, Chile.

Thanks to the Rosetta mission, our understanding of comets has greatly improved. A very good opportunity to apply this knowledge appeared in early 2017 with the appearance of the Jupiter family comet 41P/Tuttle-Giacobini-Kresak. The comet was only 0.15 au from the Earth as it passed through perihelion on April 12, 2017. We performed an observational campaign with the TRAPPIST telescopes that covered almost the entire period of time when the comet was active. In this work we present a comprehensive study of the evolution of the dust environment of 41P based on observational data from January to July, 2017. In addition, we performed numerical simulations to constrain its origin and dynamical nature. To model the observational data set we used a Monte Carlo dust tail model, which allowed us to derive the dust parameters that best describe its dust environment as a function of heliocentric distance: its dust production rate, the size distribution and ejection velocities of the dust particles, and its emission pattern. In order to study its dynamical evolution, we completed several experiments to evaluate the degree of stability of its orbit, its life time in its current region close to Earth, and its future behaviour. From the dust analysis, we found that comet 41P is a dust-poor comet compared to other comets of the same family, with a complex emission pattern that shifted from full isotropic to anisotropic ejection sometime during February 24-March 14 in 2017, and then from anisotropic to full isotropic again between June 7-28. During the anisotropic period, the emission was controlled by two strongly active areas, where one was located in the southern and one in the northern hemisphere of the nucleus. The total dust mass loss is estimated to be ~7.5×108 kg. From the dynamical simulations we estimate that ~3600 yr is the period of time during which 41P will remain in a similar orbit. Taking into account the estimated mass loss per orbit, after 3600 yr, the nucleus may lose about 30% of its mass. However, based on its observed dust-to-water mass ratio and its propensity to outbursts, the lifetime of this comet could be much shorter.

Astronomy & Astrophysics (In press)

NASA ADS: 2018arXiv180500493P arXiv: 1805.00493

The optical characteristics of the dust of sungrazing comet C/2012 S1 (ISON) observed at large heliocentric distances

  • Ivanova, O. 1,2
  • Reshetnyk, V. 2,3
  • Skorov, Yu. 4
  • Blum, J. 4
  • Seman Krišandová, Z. 1
  • Svoreň, J. 1
  • Korsun, P. 2
  • Afanasiev, V. 5
  • Luk'yanyk, I. 6
  • Andreev, M. 2,7,8
  1. Astronomical Institute of Slovak Academy of Sciences, Slovakia
  2. Main Astronomical Observatory of NAS of Ukraine, Ukraine
  3. Astronomy and Space Physics Department, Faculty of Physics, Taras Shevchenko National University of Kyiv, Ukraine
  4. University of Braunschweig, Institute for Geophysics and Extraterrestrial Physics, Germany
  5. Special Astrophysical Observatory of the Russian Academy of Science, Russia
  6. Astronomical Observatory, Taras Shevchenko National University of Kyiv, Ukraine
  7. Terskol Branch of the Institute of Astronomy of RAS, Russia
  8. International Center for Astronomical, Medical and Ecological Research NAS of Ukraine, Ukraine

We present an analysis of the photometric and spectroscopic data of the comet C/2012 S1 (ISON) observed at the heliocentric distances of 6.21–4.81 AU. The photometric observations were made with the 60-cm Zeiss-600 telescope (ICAMER, peak Terskol, Russia) and the spectroscopic observations were performed using the SCORPIO-2 focal reducer mounted in the prime focus of the 6-m BTA telescope (SAO RAS, Russia). We analyse the B, V and R-band images to describe the dusty cometary coma and to investigate its brightness, colours and dust production rate. The spectra cover the wavelength range of 3600–7070 Å. No emissions which are expected in this wavelength region were detected above the 3σ level. The continuum shows a reddening effect with the normalized gradient of reflectivity along dispersion of 9.3 ± 1.1% per 1000 Å. A dust-loss rate was derived using the obtained values and under the different model assumptions. Our simulations clearly indicate that to retrieve dust production from the observational Afρ parameter is an ambiguous task. The result of such a procedure is strongly dependent on dynamical (e.g. effective density and cross-section) as well as optical (e.g. scattering coefficient and phase function) characteristics of dust grains. A variation of the mentioned parameters can lead to dramatic changes in the evaluation of mass production. We demonstrate that the dynamic and optical properties are interconnected via the microscopic properties of dust grains (effective size and porosity).

Icarus (Published)

DOI: 10.1016/j.icarus.2018.05.008 NASA ADS: 2018Icar..313....1I arXiv: 1805.0671

Ultraviolet Observations of Coronal Mass Ejection Impact on Comet 67P/Churyumov–Gerasimenko by Rosetta Alice

  • John W. Noonan [1,2], S. Alan Stern [1], Paul D. Feldman [3], Thomas Broiles [4], Cyril Simon Wedlund [5], Niklas J. T. Edberg [6], Eric Schindhelm [7], Joel Wm. Parker [1], Brian A. Keeney [1], Ronald J. Vervack Jr [8],Andrew J. Steffl [1], Matthew M. Knight [9], Harold A. Weaver [8], Lori M. Feaga [9], Michael A'Hearn 9
  1. Southwest Research Institute
  2. Lunar and Planetary Laboratory, University of Arizona
  3. The Johns Hopkins University
  4. Space Science Institute
  5. University of Oslo
  6. Swedish Institute of Space Physics
  7. Ball Aerospace and Technology
  8. Johns Hopkins University Applied Physics Laboratory
  9. University of Maryland

The Alice ultraviolet spectrograph on the European Space Agency Rosetta spacecraft observed comet 67P/Churyumov–Gerasimenko in its orbit around the Sun for just over two years. Alice observations taken in 2015 October, two months after perihelion, show large increases in the comet's Lyβ, O I 1304, O I 1356, and C I 1657 Å atomic emission that initially appeared to indicate gaseous outbursts. However, the Rosetta Plasma Consortium instruments showed a coronal mass ejection (CME) impact at the comet coincident with the emission increases, suggesting that the CME impact may have been the cause of the increased emission. The presence of the semi-forbidden O I 1356 Å emission multiplet is indicative of a substantial increase in dissociative electron impact emission from the coma, suggesting a change in the electron population during the CME impact. The increase in dissociative electron impact could be a result of the interaction between the CME and the coma of 67P or an outburst coincident with the arrival of the CME. The observed dissociative electron impact emission during this period is used to characterize the O2 content of the coma at two peaks during the CME arrival. The mechanism that could cause the relationship between the CME and UV emission brightness is not well constrained, but we present several hypotheses to explain the correlation.

The Astronomical Journal (Published)

DOI: 10.3847/1538-3881/aac432

Implications of the Small Spin Changes Measured for Large Jupiter-Family Comet Nuclei

  • Kokotanekova, R. 1, 2
  • Snodgrass, C. 2
  • Lacerda, P. 3
  • Green, S. F. 2
  • Nikolov, P. 4
  • Bonev, T. 4
  1. Max Planck Institute for Solar System Research, Göttingen, Germany.
  2. Planetary and Space Sciences, School of Physical Sciences, The Open University, Milton Keynes, UK.
  3. Astrophysics Research Centre, Queen’s University Belfast, Belfast, UK.
  4. Institute of Astronomy and National Astronomical Observatory, Sofia, Bulgaria.

Rotational spin-up due to outgassing of comet nuclei has been identified as a possible mechanism for considerable mass-loss and splitting. We report a search for spin changes for three large Jupiter-family comets (JFCs): 14P/Wolf, 143P/Kowal-Mrkos, and 162P/Siding Spring. None of the three comets has detectable period changes, and we set conservative upper limits of 4.2 (14P), 6.6 (143P) and 25 (162P) minutes per orbit. Comparing these results with all eight other JFCs with measured rotational changes, we deduce that none of the observed large JFCs experiences significant spin changes. This suggests that large comet nuclei are less likely to undergo rotationally-driven splitting, and therefore more likely to survive more perihelion passages than smaller nuclei. We find supporting evidence for this hypothesis in the cumulative size distributions of JFCs and dormant comets, as well as in recent numerical studies of cometary orbital dynamics. We added 143P to the sample of 13 other JFCs with known albedos and phase-function slopes. This sample shows a possible correlation of increasing phase-function slopes for larger geometric albedos. Partly based on findings from recent space missions to JFCs, we hypothesise that this correlation corresponds to an evolutionary trend for JFCs. We propose that newly activated JFCs have larger albedos and steeper phase functions, which gradually decrease due to sublimation-driven erosion. If confirmed, this could be used to analyse surface erosion from ground and to distinguish between dormant comets and asteroids.

Monthly Notices of the Royal Astronomical Society (In press)

DOI: 10.1093/mnras/sty1529 NASA ADS: 2018MNRAS.tmp.1458K arXiv: 1806.02897