Cometary Science Newsletter

Issue
59
Month
February 2020
Editor
Michael S. P. Kelley (msk@astro.umd.edu)

Post-doc position in asteroid/comet science

The Institute for Astronomy at the University of Edinburgh is offering a post-doc position on asteroid/comet observations, funded as part of the EU NEOROCKS programme on near-Earth asteroids. This is a one year position, which will hopefully be extended depending on future applications for funding to extend the work for other surveys (e.g. LSST, maybe EUCLID). The main goal will be to develop software that will be useful for surveys to search for faint comet-like activity.

To view details, go to https://www.vacancies.ed.ac.uk/pls/corehrrecruit/erq_jobspec_version_4.jobspec?p_id=051083.

For informal enquiries, please contact Colin Snodgrass (csn@roe.ac.uk)

Comet 2I/Borisov Observing Campaign

In conjunction with the 46P/Wirtanen Observing campaign, we have initiated a basic level observing campaign for comet 2I/Borisov, to track planned/scheduled/obtained observations of this unique object, as well as providing occasional updates on measurements that have been reported.

We encourage you to go to the website and submit your observing plans.

You can access the site at http://iawn.net/obscamp/Borisov/

Conference Announcements

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

The 13th meeting on Cosmic Dust

URL: https://www.cps-jp.org/~dust

VENUE: Kitakyushu International Conference Center, Kitakyushu, JAPAN

DATE: Aug. 17–21, 2020

OBJECTIVES: This series of Cosmic Dust meetings aims at finding a consensus among experts on the formation and evolution of cosmic dust: where it comes from and where it goes. The meeting is organized by dust freaks who are very enthusiastic not only to make the goal achievable but also to establish a dust community across every scientifically relevant discipline for the development of cosmic dust research. For this reason, the primary objective of the meeting is to bring together professionals who deal with cosmic dust as well as provide an opportunity for participants to develop interpersonal relationships and scientific interactions among themselves.

SCOPE: All kinds of cosmic dust such as intergalactic dust, circumnuclear dust, interstellar dust, protoplanetary disk dust, debris disk dust, cometary dust, interplanetary dust, circumplanetary dust, stellar nebular condensates, presolar grains, micrometeorites, meteoroids, meteors, regolith particles, planetary aerosols are the subject of discussion. The meeting is open for any aspects of dust research by means of different methods of studies (in-situ and laboratory measurements, astronomical observations, laboratory and numerical simulations, theoretical modeling, data analyses, etc.). Also welcome are papers on dust-related topics.

REGISTRATION FEE: 15,000 JPY (Early-bird rate: 10,000 JPY)

ADMISSIONS: 50 participants (determined at the SOC's discretion)

DEADLINE FOR ADMISSIONS APPLICATION: May 8, 2020, 11:59 p.m. JST

SOC: Jean-Charles Augereau, Cornelia Jäger, Hidehiro Kaneda, Hiroshi Kimura [Chair], Ludmilla Kolokolova, Aigen Li, Hiroki Senshu

LOC: Hiroki Chihara, Takayuki Hirai, Hidehiro Kaneda, Hiroshi Kimura, Hiroshi Kobayashi, Takaya Nozawa, Takaya Okamoto, Tomomi Omura, Takafumi Ootsubo, Hiroki Senshu [Chair], Takashi Shimonishi, Koji Wada

CONTACT: dust-inquiries@cps-jp.org

Refereed Articles

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

Spitzer Space Telescope observations of bilobate comet 8P/Tuttle

  • O. Groussin 1
  • L. Lamy 2
  • M. S. P. Kelley 3
  • I. Toth 4
  • L. Jorda 1
  • Y. R. Fernández 5
  • H. A. Weaver 6
  1. Aix Marseille Univ, CNRS, CNES, LAM, Marseille, France
  2. Laboratoire Atmosphères, Milieux et Observations Spatiales, CNRS & UVSQ, 11 bvd d’Alembert, 78280 Guyancourt, France
  3. Department of Astronomy, University of Maryland, College Park, MD 20742-2421, USA
  4. MTA CSFK Konkoly Observatory, H1121 Budapest, Konkoly Thege M. ut 15-17., Hungary
  5. Department of Physics and Florida Space Institute, University of Central Florida, Orlando, FL 32816, USA
  6. The Johns Hopkins University Applied Physics Laboratory, Laurel, MD 20723, USA

Context. Comet 8P/Tuttle is a nearly isotropic comet (NIC) whose physical properties are poorly known and might be different from those of ecliptic comets (EC) owing to their different origin. Two independent observations have shown that 8P/Tuttle has a bilobate nucleus.

Aims. Our goal is to determine the physical properties of the nucleus (size, shape, thermal inertia, and albedo) and coma (water and dust) of 8P/Tuttle.

Methods. We observed the inner coma of 8P/Tuttle with the infrared spectrograph (IRS) and the infrared camera (MIPS) of the Spitzer Space Telescope (SST). We obtained one spectrum (5 – 40 μm) on 2 November 2007 and a set of 19 images at 24 μm on 22 – 23 June 2008 sampling the rotational period of the nucleus. The data were interpreted using thermal models for the nucleus and the dust coma, and we considered two possible shape models of the nucleus derived from Hubble Space Telescope visible and Arecibo radar observations.

Results. We favor a model for the nucleus shape that is composed of two contact spheres with respective radii of 2.7 ± 0.1 km and 1.1 ± 0.1 km and a pole orientation with RA = 285 ± 12 deg and DEC = +20 ± 5 deg. The thermal inertia of the nucleus lies in the range 0 – 100 J K−1 m−2 s−1/2 and the R-band geometric albedo is 0.042 ± 0.008. The water production rate amounts to 1.1±0.2×1028 molecules s−1 at 1.6 AU from the Sun pre-perihelion, which corresponds to an active fraction of ≈9%. At the same distance, the Afρ quantity amounts to 310 ± 34 cm, and it reaches 325 ± 36 cm at 2.2 AU post-perihelion. The dust grain temperature is estimated to be 258 ± 10 K, which is 37 K higher than the thermal equilibrium temperature at 1.6 AU. This indicates that the dust grains that contribute to the thermal infrared flux have a typical size of ≈10 μm. The dust spectrum exhibits broad emission around 10 μm (1.5σ confidence level) and 18 μm (5σ confidence level) that we attribute to amorphous pyroxene.

Astronomy & Astrophysics (Published)

DOI: 10.1051/0004-6361/201936458

Detection of a Water Tracer in Interstellar Comet 2I/Borisov

  • McKay, A. 1,2
  • Cochran, A. 3
  • Dello Russo, N. 4
  • and DiSanti, M. 1
  1. NASA GSFC, Greenbelt, MD
  2. American University, Washington, D.C.
  3. University of Texas at Austin/McDonald Observatory
  4. Johns Hopkins Applied Physics Laboratory

We present high spectral resolution optical spectra obtained with the ARCES instrument at Apache Point Observatory showing detection of the [OI] 6300 Å line in interstellar comet 2I/Borisov. We employ the observed flux in this line to derive an H2O production rate of (6.3 ± 1.5) × 1026 mol/s. Comparing to previously reported observations of CN, this implies a CN/H2O ratio of ~0.3%–0.6%. The lower end of this range is consistent with the average value in comets, while the upper end is higher than the average value for solar system comets, but still within the range of observed values. C2/H2O is depleted, with a value likely less than 0.1%. The dust-to-gas ratio is consistent with the normal value for solar system comets. Using a simple sublimation model we estimate an H2O active area of 1.7 km2, which for current estimates for the size of Borisov suggests active fractions between 1% and 150%, consistent with values measured in solar system comets. More detailed characterization of 2I/Borisov, including compositional information and properties of the nucleus, is needed to fully interpret the observed H2O production rate.

Astrophysical Journal Letters (Published)

DOI: 10.3847/2041-8213/ab64ed arXiv: 1910.12785

Probing the Evolutionary History of Comets: An Investigation of the Hypervolatiles CO, CH4, and C2H6 in the Jupiter-family Comet 21P/Giacobini-Zinner

  • Nathan X. Roth 1,2,12
  • Erika L. Gibb 1,3,12
  • Boncho P. Bonev 4,12
  • Michael A. DiSanti 3,5,12
  • Neil Dello Russo 6,12
  • Adam J. McKay 4,5,12
  • Ronald J. Vervack, Jr. 6,12
  • Hideyo Kawakita 7,12
  • Mohammad Saki 1,12
  • Nicolas Biver 8,12
  • Dominique Bockelée-Morvan 8,12
  • Lori M. Feaga 9,12
  • Nicolas Fougere 10,12
  • Anita L. Cochran 11,12
  • Michael Combi 10,12
  • Yinsi Shou 10,12
  1. Department of Physics & Astronomy, University of Missouri-St. Louis, One University Boulevard, St. Louis, MO, USA
  2. Solar System Exploration Division, Astrochemistry Laboratory Code 691, NASA-Goddard Space Flight Center, Greenbelt, MD, USA
  3. Goddard Center for Astrobiology, NASA-Goddard Space Flight Center, Greenbelt, MD, USA
  4. Department of Physics, American University, Washington, DC, USA
  5. Solar System Exploration Division, Planetary System Laboratory Code 693, NASA-Goddard Space Flight Center, Greenbelt, MD, USA
  6. Johns Hopkins Applied Physics Laboratory, Laurel, MD, USA
  7. Koyoma Astronomical Observatory, Kyoto Sangyo University Motoyama, Kamingamo, Kita-ku, Kyoto 603-8555, Japan
  8. LESIA, Observatoire de Paris, PSL Research University, CNRS, Sorbonne Université, Université de Paris, Sorbonne Paris Cité, Meudon, France
  9. Department of Astronomy, University of Maryland, College Park, MD, USA
  10. Department of Climate and Space Sciences and Engineering, University of Michigan, Ann Arbor, MI, USA
  11. McDonald Observatory, University of Texas at Austin, Austin, TX, USA
  12. Visiting Astronomer at the Infrared Telescope Facility, which is operated by the University of Hawaii under contract NNH14CK55B with the National Aeronautics and Space Administration

Understanding the cosmogonic record encoded in the parent volatiles stored in cometary nuclei requires investigating whether evolution (thermal or otherwise) has modified the composition of short-period comets during successive perihelion passages. As the most volatile molecules systematically observed in comets, the abundances of CO, CH4, and C2H6 in short-period comets may serve to elucidate the interplay between natal conditions and post-formative evolution in setting present-day composition, yet secure measurements of CO and CH4 in Jupiter-family comets (JFCs) are especially sparse. The highly favorable 2018 apparition of JFC 21P/Giacobini─Zinner enabled a sensitive search for these “hypervolatiles” in a prototypical carbon-chain depleted comet. We observed 21P/Giacobini─Zinner with the iSHELL spectrograph at the NASA Infrared Telescope Facility on four pre-perihelion dates, two dates near-perihelion, and one post-perihelion date. We obtained detections of CO, CH4, and C2H6 simultaneously with H2O on multiple dates. We present rotational temperatures, production rates, and mixing ratios. Combined with previous work, our results may indicate that the hypervolatile coma composition of 21P/Giacobini─Zinner was variable across apparitions as well as within a particular perihelion passage, yet the spread in these measurements is a relatively small fraction of the variation in each molecule from comet to comet. We discuss the implications of our measured hypervolatile content of 21P/Giacobini─Zinner for the evolution of JFCs, and place our results in the context of findings from the Rosetta mission and ground-based studies of comets.

The Astronomical Journal (Published)

DOI: 10.3847/1538-3881/ab536b NASA ADS: 2020AJ....159...42R

Post-perihelion volatile production and release from Jupiter-family comet 45P/Honda-Mrkos-Pajdušáková

  • Neil Dello Russo 1
  • Hideyo Kawakita 2
  • Boncho P. Bonev 3
  • Ronald J. Vervack Jr. 1
  • Erika L. Gibb 4
  • Yoshiharu Shinnaka 2
  • Nathan X. Roth 4
  • Michael A. DiSanti 5,6
  • Adam J. McKay 3,5, 7
  1. Space Department, Johns Hopkins Applied Physics Laboratory, Laurel MD 20723, USA
  2. Koyama Astronomical Observatory, Kyoto Sangyo University Motoyama, Kita-ku, Kyoto 603-8555, Japan
  3. Department of Physics, American University, Washington, DC, USA
  4. Department of Physics and Astronomy, University of Missouri-St. Louis, St. Louis, MO, USA
  5. Solar System Exploration Division, Planetary Systems Laboratory Code 693, NASA-Goddard Space Flight Center, Greenbelt, MD, USA
  6. Goddard Center for Astrobiology, NASA-Goddard Space Flight Center, Greenbelt, MD, USA
  7. University Space Research Association/NASA Postdoctoral Program, Columbia, MD, USA

High-resolution infrared spectra of Jupiter-family comet 45P/Honda-Mrkos-Pajdušáková were obtained with NIRSPEC at the W. M. Keck Observatory on two post-perihelion dates (UT 2017 February 13 and 19), when the comet was at heliocentric distances of 1.01 and 1.10 AU, respectively. On UT February 13, H2O was measured simultaneously with six trace parent molecules: CH3OH, C2H6, HCN, NH3, C2H2, and H2CO. On UT February 19, CH4 and CO were also targeted in addition to the species measured on UT February 13. Abundances of CO, CH4, and C2H2 relative to H2O are consistent with values obtained from IRTF/iSHELL observations of 45P in early January 2017 just after perihelion when the heliocentric distance was 0.55 – 0.56 AU. Differences are seen in H2CO/H2O, C2H6/H2O, CH3OH/H2O, and HCN/H2O in February compared to January. Additionally, NH3 abundances appear highly variable during the February measurements, suggesting possible fluctuations of a factor of ten; however, there is significant uncertainty in quantifying NH3 owing to the marginal detections of only one or two lines on each of the two dates. Combining all infrared spectroscopic observations of 45P in January and February 2017, a post-perihelion relationship of Q(H2O) = (2.81 ± 0.25) x 1027 [Rh(-3.83±0.18)] molecules s-1 is derived. However, all measurements suggest significant variability in H2O production on timescales of hours and days. Compared to other comets, volatile abundances relative to H2O in 45P are as follows: CO (depleted relative to all measured comets), CH3OH (enriched/all comets), CH4 and C2H6 (typical/all comets, enriched/Jupiter-family comets), C2H2 (depleted/all comets, typical/Jupiter-family comets), H2CO (January: typical, February depleted/all comets), HCN (January: severely depleted, February: typical/Jupiter-family comets). The small geocentric distances of the comet in February 2017 provide high spatial resolution in the coma of 45P (~ 12 and 19 km/pixel on February 13 and 19, respectively). Overall, the spatial distributions of volatiles and dust suggest a relatively symmetric and uniform coma during the UT February 13 and 19 observations, with small spatial differences noted between some volatile species. Measured C2H2 and HCN abundances are consistent with HCN as the primary parent of CN and C2H2 as a significant but not primary parent for C2, based on C2 and CN production rate measurements from the 2017 and previous apparitions. Extracted spectra show an increase in the dust-to-gas ratio in 45P from February 13 to 19 in agreement with contemporaneous narrowband optical measurements.

Icarus (Published)

DOI: 10.1016/j.icarus.2019.113411 NASA ADS: 2020Icar..33513411D

ALMA and ROSINA detections of phosphorus-bearing molecules: the interstellar thread between star-forming regions and comets

  • V. M. Rivilla 1
  • M. N. Drozdovskaya 2
  • K. Altwegg 3
  • P. Caselli 4
  • M. T. Beltrán 1
  • F. Fontani 1
  • F. F. S. van der Tak 5,6
  • R. Cesaroni 1
  • A. Vasyunin 7,8
  • M. Rubin 2
  • F. Lique 9
  • S. Marinakis 10,11
  • L. Testi 1,12,13
  • and the ROSINA team
  1. INAF-Osservatorio Astrofisico di Arcetri, Largo Enrico Fermi 5, I-50125, Florence, Italy
  2. Center for Space and Habitability, University of Bern, Gesellschaftsstrasse 6, CH-3012 Bern, Switzerland
  3. Physikalisches Institut, University of Bern, Sidlerstrasse 5, CH-3012 Bern, Switzerland
  4. Max-Planck-Institute for Extraterrestrial Physics, Garching, 85741, Germany
  5. SRON Netherlands Institute for Space Research, Landleven 12, NL-9747 AD Groningen, the Netherlands
  6. Kapteyn Astronomical Institute, University of Groningen, 9747 AD, Groningen, the Netherlands
  7. Ural Federal University, Ekaterinburg, 620002, Russia
  8. Visiting Leading Researcher, Engineering Research Institute ‘Ventspils International Radio Astronomy Centre’ of Ventspils University of Applied Sciences, Inzˇenieru 101, Ventspils LV-3601, Latvia
  9. LOMC, UMR 6294, CNRS-Universite du Havre, France
  10. School of Health, Sport and Bioscience, University of East London, Stratford Campus, Water Lane, London E15 4LZ, UK
  11. Department of Chemistry and Biochemistry, School of Biological and Chemical Sciences, Queen Mary University of London, Joseph Priestley Building, Mile End Road, London E1 4NS, UK
  12. ESO/European Southern Observatory, Karl Schwarzschild str. 2, D- 85748, Garching, Germany
  13. Excellence Cluster ‘Universe’ , Boltzmann str. 2, D-85748 Garching bei Muenchen, Germany

To understand how phosphorus (P)-bearing molecules are formed in star-forming regions, we have analysed the Atacama Large Millimeter/Submillimeter Array (ALMA) observations of PN and PO towards the massive star-forming region AFGL 5142, combined with a new analysis of the data of the comet 67P/Churyumov-Gerasimenko taken with the Rosetta Orbiter Spectrometer for Ion and Neutral Analysis (ROSINA) instrument onboard Rosetta. The ALMA maps show that the emission of PN and PO arises from several spots associated with low-velocity gas with narrow linewidths in the cavity walls of a bipolar outflow. PO is more abundant than PN in most of the spots, with the PO/PN ratio increasing as a function of the distance to the protostar. Our data favour a formation scenario in which shocks sputter phosphorus from the surface of dust grains, and gas-phase photochemistry induced by UV photons from the protostar allows efficient formation of the two species in the cavity walls. Our analysis of the ROSINA data has revealed that PO is the main carrier of P in the comet, with PO/PN > 10. Since comets may have delivered a significant amount of prebiotic material to the early Earth, this finding suggests that PO could contribute significantly to the phosphorus reservoir during the dawn of our planet. There is evidence that PO was already in the cometary ices prior to the birth of the Sun, so the chemical budget of the comet might be inherited from the natal environment of the Solar system, which is thought to be a stellar cluster including also massive stars.

Monthly Notices of the Royal Astronomical Society (Published)

DOI:  10.1093/mnras/stz3336 NASA ADS:  2020MNRAS.492.1180R arXiv: 1911.11647

The morphological, elastic, and electric properties of dust aggregates in comets: A close look at COSIMA/Rosetta’s data on dust in comet 67P/ Churyumov-Gerasimenko

  • Hiroshi Kimura 1, 2
  • Martin Hilchenbach 2
  • Sihane Merouane 2
  • John Paquette 2
  • Oliver Stenzel 2
  1. Planetary Exploration Research Center (PERC), Chiba Institute of Technology, Japan
  2. Max Planck Institute for Solar System Research, Germany

The Cometary Secondary Ion Mass Analyzer (COSIMA) onboard ESA’s Rosetta orbiter has revealed that dust particles in the coma of comet 67P/Churyumov-Gerasimenko are aggregates of small grains. We study the morphological, elastic, and electric properties of dust aggregates in the coma of comet 67P/Churyumov-Gerasimenko using optical microscopic images taken by the COSIMA instrument. Dust aggregates in COSIMA images are well represented as fractals in harmony with morphological data from MIDAS (Micro-Imaging Dust Analysis System) and GIADA (Grain Impact Analyzer and Dust Accumulator) onboard Rosetta. COSIMA’s images, together with the data from the other Rosetta’s instruments such as MIDAS and GIADA do not contradict the so-called rainout growth of 10 μm-sized particles in the solar nebula. The elastic and electric properties of dust aggre- gates measured by COSIMA suggest that the surface chemistry of cometary dust is well represented as carbonaceous matter rather than silicates or ices, consistent with the mass spectra, and that organic matter is to some extent carbonized by solar radiation, as inferred from optical and infrared observations of various comets. Electrostatic lofting of cometary dust by intense electric fields at the terminator of its parent comet is unlikely, unless the surface chemistry of the dust changes from a dielectric to a conductor. Our findings are not in conflict with our current understanding of comet formation and evolution, which begin with the accumulation of condensates in the solar nebula and follow with the formation of a dust mantle in the inner solar system.

Planetary and Space Science (Published)

DOI: 10.1016/j.pss.2019.104825 NASA ADS: 2020P&SS..18104825K arXiv: 1912.13198