Cometary Science Newsletter

Issue
24
Month
March 2017
Editor
Michael S. P. Kelley (msk@astro.umd.edu)

Conference Announcements

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

Planet Formation and Evolution 2017

Location & Dates

Jena, Germany; 25-27th September 2017

Rationale

The German community of researchers working in the fields of planet formation, exoplanets and planetary systems, protoplanetary and debris disks, astrobiology, and planetary research in general has organized the "Planet Formation and Evolution" workshops since 2001. The meetings in the series are typically held every 1.5 years at different German universities that host research groups actively working on these topics. This workshop is the 11th in the series. PFE meetings are usually attended by scientists from all parts of Germany with a broad international participation. Following the spirit of the previous very stimulating meetings, the goal of this workshop is to provide a common platform for scientists working in the fields listed above. Most importantly, this workshop is aimed at stimulating and intensifying the dialogue between researchers using various approaches - observations, theory, and laboratory studies. In particular, students and postdocs are encouraged to present their results and to use the opportunity to learn more about the main questions and most recent results in adjacent fields.

Topics

  • Dust, Pebbles, Planetesimals
  • Protoplanetary and Transitional Disks
  • Exoplanet Observations
  • Exoplanet Interiors, Atmospheres, and Habitability
  • Planetary System Dynamics
  • Debris Disks
  • Solar System

Confirmed Invited Speakers

  • Anthony Boccaletti (Paris)
  • Carsten Guettler (Goettingen)
  • Grant Kennedy (Cambridge)
  • Zoe Leinhardt (Bristol)
  • Nadine Nettelmann (Rostock)
  • Ilaria Pascucci (Arizona)
  • Sean Raymond (Bordeaux)
  • Ignas Snellen (Leiden)

Registration and Abstract Submission

Registration and abstract submission through the workshop website are now open. Make sure to register early, as the number of participants is limited to 150. Final deadline is 1st June.

Website

http://www.astro.uni-jena.de/~pfe2017

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.

46P/Wirtanen Campaign, 45P/H-M-P and 41P/T-G-K, too

The website for the Comet 46P/Wirtanen Campaign is now online.

The Comet Group at the University of Maryland is organizing a campaign to provide general information about Comet 46P/Wirtanen and to coordinate observations during its 2018 apparition. Leading up to the Wirtanen event, we are providing the same services for comets 45P/Honda-Mrkos-Pajdusakova and 41P/Tuttle-Giacobini-Kresak.

All three comets make close approaches to the Earth, offering prime conditions for high-resolution imaging and spectroscopic observations, and visibility allowing coverage for many hours per night for extended periods of time. With Wirtanen predicted to reach naked eye brightness, and the others visible with small telescopes or binoculars, these close approaches also represent excellent opportunities for engaging the public and raising awareness about cometary science and astronomy in general.

The Campaign website is located at wirtanen.astro.umd.edu

Tony Farnham, UMD

Refereed Articles

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

Split Active Asteroid P/2016 J1 (PANSTARRS)

  • Hui, Man-To 1
  • Jewitt, David 1,2
  • Du, Xinnan 2
  1. Department of Earth, Planetary, and Space Sciences, UCLA
  2. Department of Physics and Astronomy, UCLA

We present a photometric and astrometric study of the split active asteroid P/2016 J1 (PANSTARRS). The two components (hereafter J1-A and J1-B) separated either ~1500 days (2012 May to June) or 2300 days (2010 April) prior to the current epoch, with a separation speed Vsep = 0.70 ± 0.02 m s-1 for the former scenario, or 0.83 ± 0.06 m s-1 for the latter. Keck photometry reveals that the two fragments have similar, Sun-like colors which are comparable to the colors of primitive C- and G-type asteroids. With a nominal comet-like albedo, pR = 0.04, the effective, dust-contaminated cross sections are estimated to be 2.4 km2 for J1-A, and 0.5 km2 for J1-B. We estimate that the nucleus radii lie in the range 140 ≲ RN ≲ 900 m for J1-A and 40 ≲ RN ≲ 400 m, for J1-B. A syndyne-synchrone simulation shows that both components have been active for 3 to 6 months, by ejecting dust grains at speeds ~0.5 m s-1 with rates ~1 kg s-1 for J1-A and 0.1 kg s-1 for J1-B. In its present orbit, the rotational spin-up and devolatilization times of 2016 J1 are very small compared to the age of the solar system, raising the question of why this object still exists. We suggest that ice that was formerly buried within this asteroid became exposed at the surface, perhaps via a small impact, and that sublimation torques then rapidly drove it to break-up. Further disintegration events are anticipated due to the rotational instability.

The Astronomical Journal (In press)

arXiv: 1702.02766

ALMA mapping of rapid gas and dust variations in comet C/2012 S1 (ISON): new insights into the origin of cometary HNC

  • M. A. Cordiner 1,2
  • J. Boissier 3
  • S. B. Charnley 1
  • A. J. Remijan 4
  • M. J. Mumma 1
  • G. Villanueva 1,2
  • D. C. Lis 5
  • S. N. Milam 1
  • L. Paganini 1,2
  • J. Crovisier 6
  • D. Bockelee-Morvan 6
  • Y.-J. Kuan 7,8
  • N. Biver 6
  • I. M. Coulson 9
  1. NASA Goddard Space Flight Center, 8800 Greenbelt Road, Greenbelt, MD 20771, USA.
  2. Department of Physics, Catholic University of America, Washington, DC 20064, USA.
  3. IRAM, 300 Rue de la Piscine, 38406 Saint Martin d'Heres, France.
  4. National Radio Astronomy Observatory, Charlottesville, VA 22903, USA.
  5. LERMA, Observatoire de Paris, PSL Research University, CNRS, Sorbonne Universites, UPMC Univ. Paris 06, F-75014, Paris, France.
  6. LESIA, Observatoire de Paris, CNRS, UPMC, Universite Paris-Diderot, 5 place Jules Janssen, 92195 Meudon, France.
  7. National Taiwan Normal University, Taipei 116, Taiwan, ROC.
  8. Institute of Astronomy and Astrophysics, Academia Sinica, Taipei 106, Taiwan, ROC.
  9. East Asian Observatory, Hilo, HI 96720, USA.

Observations of the sungrazing comet C/2012 S1 (ISON) were carried out using the Atacama Large Millimeter/submillimeter Array (ALMA) at a heliocentric distance of 0.58-0.54 AU (pre-perihelion) on 2013 November 16-17. Temporally resolved measurements of the coma distributions of HNC, CH3OH, H2CO and dust were obtained over the course of about an hour on each day. During the period UT 10:10-11:00 on Nov. 16, the comet displayed a remarkable drop in activity, manifested as a >42% decline in the molecular line and continuum fluxes. The H2CO observations are consistent with an abrupt, approximately 50% reduction in the cometary gas production rate soon after the start of our observations. On Nov. 17, the total observed fluxes remained relatively constant during a similar period, but strong variations in the morphology of the HNC distribution were detected as a function of time, indicative of a clumpy, intermittent outflow for this species. Our observations suggest that at least part of the detected HNC originated from degradation of nitrogen-rich organic refractory material, released intermittently from confined regions of the nucleus. By contrast, the distributions of CH3OH and H2CO during the Nov. 17 observations were relatively uniform, consistent with isotropic outflow and stable activity levels for these species. These results highlight a large degree of variability in the production of gas and dust from comet ISON during its pre-perihelion outburst, consistent with repeated disruption of the nucleus interspersed with periods of relative quiescence.

The Astrophysical Journal (In press)

arXiv: arXiv:1702.03322

Thermal physics of the inner coma: ALMA studies of the methanol distribution and excitation in comet C/2012 K1 (PanSTARRS)

  • M. A. Cordiner 1,2
  • N. Biver 3
  • J. Crovisier 3
  • D. Bockelee-Morvan 3
  • M. J. Mumma 1
  • S. B. Charnley 1
  • G. Villanueva 1
  • L. Paganini 1,2
  • D. C. Lis 4
  • S. N. Milam 1
  • A. J. Remijan 5
  • I. M. Coulson 6
  • Y.-J. Kuan 7,8
  • J. Boissier 9
  1. NASA Goddard Space Flight Center, 8800 Greenbelt Road, Greenbelt, MD 20771, USA.
  2. Department of Physics, Catholic University of America, Washington, DC 20064, USA.
  3. LESIA, Observatoire de Paris, CNRS, UPMC, Universite Paris-Diderot, 5 place Jules Janssen, 92195 Meudon, France.
  4. LERMA, Observatoire de Paris, PSL Research University, CNRS, Sorbonne Universites, UPMC Univ. Paris 06, F-75014, Paris, France.
  5. National Radio Astronomy Observatory, Charlottesville, VA 22903, USA.
  6. East Asian Observatory, Hilo, HI 96720, USA.
  7. National Taiwan Normal University, Taipei 116, Taiwan, ROC.
  8. Institute of Astronomy and Astrophysics, Academia Sinica, Taipei 106, Taiwan, ROC.
  9. IRAM, 300 Rue de la Piscine, 38406 Saint Martin d'Heres, France.

We present spatially and spectrally-resolved observations of CH3OH emission from comet C/2012 K1 (PanSTARRS) using The Atacama Large Millimeter/submillimeter Array (ALMA) on 2014 June 28-29. Two-dimensional maps of the line-of-sight average rotational temperature (Trot) were derived, covering spatial scales 0.3''-1.8'' (corresponding to sky-projected distances ρ~500-2500 km). The CH3OH column density distributions are consistent with isotropic, uniform outflow from the nucleus, with no evidence for extended sources of CH3OH in the coma. The Trot(ρ) radial profiles show a significant drop within a few thousand kilometers of the nucleus, falling from about 60 K to 20 K between ρ=0 and 2500 km on June 28, whereas on June 29, Trot fell from about 120 K to 40 K between ρ=0 km and 1000 km. The observed Trot behavior is interpreted primarily as a result of variations in the coma kinetic temperature due to adiabatic cooling of the outflowing gas, as well as radiative cooling of the CH3OH rotational levels. Our excitation model shows that radiative cooling is more important for the J=7-6 transitions (at 338 GHz) than for the K=3-2 transitions (at 252 GHz), resulting in a strongly sub-thermal distribution of levels in the J=7-6 band at ρ≳1000 km. For both bands, the observed temperature drop with distance is less steep than predicted by standard coma theoretical models, which suggests the presence of a significant source of heating in addition to the photolytic heat sources usually considered.

The Astrophysical Journal (In press)

NASA ADS: 2017arXiv170108258C arXiv: arXiv:1701.08258

Imaging observations of the hydrogen coma of comet 67P/Churyumov-Gerasimenko in 2015 September by the PROCYON/LAICA

  • Shinnaka, Y. 1,2
  • Fougere, N. 3
  • Kawakita, H 4
  • Kameda, S. 5
  • Combi, M. R. 3
  • Ikezawa, S. 5
  • Seki, A. 5
  • Kuwabara, M. 6
  • Sato, M. 5
  • Taguchi, M. 5
  • Yoshikawa, I 6
  1. National Astronomical Observatory of Japan, Japan
  2. Université de Liège, Belgium
  3. University of Michigan, USA
  4. Kyoto Sangyo University, Japan
  5. Rikkyo University, Japan
  6. The University of Tokyo, Japan

The water production rate of a comet is one of the fundamental parameters necessary to understand cometary activity when a comet approaches the Sun within 2.5 au, because water is the most abundant icy material in the cometary nucleus. Wide-field imaging observations of the hydrogen Lyα emission in comet 67P/Churyumov–Gerasimenko were performed by the Lyman Alpha Imaging Camera (LAICA) on board the 50 kg class micro spacecraft, the Proximate Object Close Flyby with Optical Navigation (PROCYON), on UT 2015 September 7.40, 12.37, and 13.17 (corresponding to 25.31, 30.28, and 31.08 days after the perihelion passage of the comet, respectively). We derive the water production rates, QH2O, of the comet from Lyα images of the comet by using a 2D axi-symmetric Direct Simulation Monte-Carlo model of the atomic hydrogen coma; (1.46 ± 0.47) × 1028, (1.24 ± 0.40) × 1028, and (1.30 ± 0.42) × 1028 molecules s−1 on 7.40, 12.37, and 13.17 September, respectively. These values are comparable to the values from in situ measurements by the Rosetta instruments in the 2015 apparition and the ground-based and space observations during the past apparitions. The comet did not show significant secular change in average water production rates just after the perihelion passage for the apparitions from 1982 to 2015. We emphasize that the measurements of absolute QH2O based on the wide field of view (e.g., by the LAICA/PROCYON) are so important to judge the soundness of the coma models used to infer QH2O based on in situ measurements by spacecraft, like the Rosetta.

The Astronomical Journal (Published)

DOI: 10.3847/1538-3881/153/2/76 NASA ADS: 2017AJ....153...76S

The Chemical Composition of an Extrasolar Kuiper-Belt-Object

  • S. Xu 1
  • B. Zuckerman 2
  • P. Dufour 3
  • E. D. Young 4
  • B. Klein 2
  • M. Jura 2
  1. European Southern Observatory, Germany
  2. Department of Physics and Astronomy, University of California, Los Angeles, USA
  3. Universite de Montreal, Canada
  4. Department of Earth, Planetary, and Space Sciences, University of California, Los Angeles, USA

The Kuiper Belt of our solar system is a source of short-period comets that may have delivered water and other volatiles to Earth and the other terrestrial planets. However, the distribution of water and other volatiles in extrasolar planetary systems is largely unknown. We report the discovery of an accretion of a Kuiper-Belt-Object analog onto the atmosphere of the white dwarf WD 1425+540. The heavy elements C, N, O, Mg, Si, S, Ca, Fe, and Ni are detected, with nitrogen observed for the first time in extrasolar planetary debris. The nitrogen mass fraction is ∼2%, comparable to that in comet Halley and higher than in any other known solar system object. The lower limit to the accreted mass is ∼1022 g, which is about one hundred thousand times the typical mass of a short-period comet. In addition, WD 1425+540 has a wide binary companion, which could facilitate perturbing a Kuiper-Belt-Object analog into the white dwarf's tidal radius. This finding shows that analogs to objects in our Kuiper Belt exist around other stars and could be responsible for the delivery of volatiles to terrestrial planets beyond.

The Astrophysical Journal, Letters (Published)

DOI: 10.3847/2041-8213/836/1/L7 NASA ADS: 2017ApJ...836L...7X arXiv: 1702.02868