Cometary Science Newsletter

January 2017
Michael S. P. Kelley (

Refereed Articles

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

Analysis of R-band Observations of an Outburst of Comet 29P/Schwassmann-Wachmann 1 to Place Constraints on the Nucleus’ Rotation State

  • Schambeau, C. A. 1
  • Fernández, Y. R. 1
  • Samarasinha, N. H. 2
  • Mueller, B. E. A. 2
  • Woodney, L. M. 3
  1. University of Central Florida
  2. Planetary Science Institute
  3. California State University San Bernardino

We present analysis of five nights of R-band observations of Comet 29P/Schwassmann-Wachmann 1 (SW1) taken on September 2008 which show the comet undergoing an outburst. Coma morphology shows a projected asymmetric shell of material expanding radially and four linear features on the northern side of the coma at position angles 37°, 78°, 300°, and 353°. Using the measured projected radial outflow velocity of 0.11 ± 0.02 km/s for the shell material, we calculate an outburst time of UT 2008-09-21.03 ± 0.95 days. By tracking the inner and outer extent of the northern linear features, we found that the features are fully contained within the expanding shell of material. This suggested both shell and linear features originated during the same event and activity originating from different regions on the nuclear surface are not necessary to generate both types of morphological structure observed. A 3-D Monte Carlo coma model was used to model the outburst. Morphological features present in the observations were modeled allowing constraints to be placed on the spin state of SW1’s nucleus. The evolution of morphological features allows constraints on the rotation period P assuming an outburst duration Δt and the spin period constraints are expressed in terms of their ratio P/Δt. Since the spin-pole orientation could not be constrained, four spin-pole orientations were chosen for modeling the coma. Spin-period constraints for each assumed pole orientation are discussed. Overall, modeling suggested either a spin period on the order of days, a spin-pole orientation nearly along the sub-Earth direction, or a combination of both. To place an independent constraint on the outburst duration, radial surface-brightness profiles of the observations were compared with profiles from synthetic models, giving an upper-limit of Δt ≤ 1.5 days. Longer outbursts resulted in a higher number of dust grains in close proximity to the nucleus during the observations and a profile slope too steep to model observations. Lastly, from photometry of the five nights of observation, a lower limit of (1.8 ± 0.07) × 109 kg was estimated for the total amount of dust emitted during the outburst. Assuming the outburst was triggered by either the sublimation of pure CO or CO2 ice and a dust to gas ratio of ∼ 4 (Rosetta results for Comet 67P, Rotundi et al. 2015), a lower limit for the outburst duration on the order of hours was obtained.

Icarus (In press)

DOI: 10.1016/j.icarus.2016.11.026

Catastrophic Disruption of Comet ISON

  • Jacqueline V. Keane 1,2
  • Stefanie N. Milam 3
  • Iain M. Coulson 4
  • Jan T. Kleyna 1
  • Zdenek Sekanina 5
  • Rainer Kracht 6
  • Timm-Emmanuel Riesen 1,2
  • Karen J. Meech 1,2
  • Steven B. Charnley 3
  1. Institute for Astronomy, University of Hawaii, 2680 Woodlawn Drive, Honolulu, HI 96822, USA;
  2. NASA Astrobiology Institute, Honolulu, HI 96822, USA
  3. Astrochemistry Laboratory, NASA GSFC, MS 690, Greenbelt, MD 20771, USA
  4. Joint Astronomy Center, 660 North Aohoku Place, Hilo, HI 96720, USA
  5. Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109, USA
  6. Ostlandring 53, D-25335 Elmshorn, Schleswig-Holstein, Germany

We report submillimeter 450 and 850 μm dust continuum observations for comet C/2012 S1 (ISON) obtained at heliocentric distances 0.31–0.08 au prior to perihelion on 2013 November 28 (rh = 0.0125 au). These observations reveal a rapidly varying dust environment in which the dust emission was initially point-like. As ISON approached perihelion, the continuum emission became an elongated dust column spread out over as much as 60″ (>105 km) in the anti-solar direction. Deconvolution of the November 28.04 850 μm image reveals numerous distinct clumps consistent with the catastrophic disruption of comet ISON, producing ∼5.2 × 1010 kg of submillimeter-sized dust. Orbital computations suggest that the SCUBA-2 emission peak coincides with the comet's residual nucleus.

The Astrophysical Journal (Published)

DOI: 10.3847/0004-637X/831/2/207 NASA ADS: 2016ApJ...831..207K

Possible Thermoluminescence of the Solid Cometary Substance: Thermoluminescence of Cometary Substance

  • Irakli Simonia 1
  1. Ilia State University, the School of Natural Sciences and Engineering

The article describes a mechanism of the possible thermoluminescence of solid cometary substances, including dusty halos. We propose to consider comet flares as the thermoluminescence of the cometary ices and mineral dust. The article provides the results of some laboratory experiments on frozen phosphorescence of a number of minerals (quartz, forsterite, and diamond) conducted over the past several years and relevant for reviewing the given problem. We also propose a concept of the comet’s luminescent relictography and some scientific initiations. Properties of red and blue thermoluminescence flares of cometary halos are described, and we consider the similarity of thermoluminescence and cathodoluminescence processes of cometary dust. Various aspects of the problem are under discussion.

The Astronomical Journal (Published)

DOI: 10.3847/0004-6256/152/4/87 NASA ADS: 2016AJ....152...87S

Asteroid-Comet Continuum Objects in the Solar System

  • Hsieh, H. H. 1,2
  1. Planetary Science Institute, USA
  2. Academia Sinica Institute of Astronomy and Astrophysics, Taiwan

In this review presented at the Royal Society meeting, "Cometary Science After Rosetta", I present an overview of studies of small solar system objects that exhibit properties of both asteroids and comets (with a focus on so-called active asteroids). Sometimes referred to as "transition objects", these bodies are perhaps more appropriately described as "continuum objects", to reflect the notion that rather than necessarily representing actual transitional evolutionary states between asteroids and comets, they simply belong to the general population of small solar system bodies that happen to exhibit a continuous range of observational, physical, and dynamical properties. Continuum objects are intriguing because they possess many of the properties that make classical comets interesting to study (e.g., relatively primitive compositions, ejection of surface and subsurface material into space where it can be more easily studied, and orbital properties that allow us to sample material from distant parts of the solar system that would otherwise be inaccessible), while allowing us to study regions of the solar system that are not sampled by classical comets.

Phil. Trans. Royal Soc. A (In press)

arXiv: 1611.09995

Hyperactivity in 103P/Hartley 2: Chunks from the sub-surface in Type IIa jet regions

  • Michael Belton 1,2
  1. Belton Space Exploration Initiatives
  2. Kitt Peak National Observatory

We analyze the observed radial distribution of column densities of water-ice particulates embedded in the primary jet region (J1) of 103P’s inner coma at altitudes between 439 and 1967 m (Protopapa et al., 2014, Icarus 238, 191-204) and determine the speed and acceleration of particles and their mass-flow within the filaments of the jet. This is done by applying a CO2 driven (Type IIa) jet model proposed by Belton (2010, Icarus 210, 881-897). The model utilizes water-ice particles dislodged in the source regions of the jet filaments and accelerated by CO2 to explain the radial distribution of water-ice particulates. We provide an explanation for the remarkably different radial distribution of refractory dust particles by hypothesizing that the majority of the dust originates directly from the nucleus surface in inter-filament regions of the jet complex and is accelerated by H2O. Our model provides a mass-flow of water from the J1 jet complex that is ~40 times greater than the constant speed sublimation model discussed by Protopapa et al. but is still too small to explain the hyperactivity of the comet. Speeds in the flow are increased by a factor up to ~20 over those found by Protopapa et al.

To account for the hyperactivity, most of the mass dislodged in the filament source regions must be in weakly accelerated large chunks that achieve only low speeds en route to the region of observation. These chunks soon leave the filamentary jet structure due to the rotation of the nucleus and do not contribute to the column densities observed at higher altitudes in the jet filaments. Employing the results of Kelley et al. (2015. Icarus 262, 187-189)) on total cross-section and mass-flow in the coma we find that large chunks with the same bulk properties as the nucleus can increase the active fraction of the comet by two or three times. With the exception that the chunks do not need to be “nearly pure water ice”, these results support the hypothesis that hyperactivity in comet 103P/Hartley 2 is the result of super-volatiles that “…drag out chunks of nearly pure water ice that then sublime to provide a large fraction of the total H2O gaseous output of the comet” (A’Hearn et al, 2011. Science 332, 1396-1400). We find that the largest chunks (effective radius ~4 m) are probably dislodged at an average rate less than 1 chunk / filament / 1- 3 rotation periods near perihelion and we estimate that the filamentary source regions, if 50 - 100m in diameter, could be excavated to a depth of 44 - 171m in a single perihelion passage. We note similarities with groups of active pits discovered on 67P (Vincent et al., 2015. Nature 523, 63 – 66) and suggest that these features may have, in the past, supported Type IIa super-volatile jet outflows that are now essentially exhausted.

Icarus (In press)

DOI: 10.1016/j.icarus 2016.12.021