Cometary Science Newsletter

Issue
20
Month
November 2016
Editor
Michael S. P. Kelley (msk@astro.umd.edu)

TRAPPIST-North First Light

On October 6, TRAPPIST-North has been inaugurated at the Oukaimeden Observatory in the Atlas mountains in Morocco (2750 m) in presence of scientists of the Cadi Ayyad University of Marrakech and astronomers from the University of Liège. TRAPPIST-North is the twin of the telescope that was installed in 2010 at the observatory of La Silla in Chile. It has the same goals as his predecessor: the detection and study of exoplanets, and the study of comets and other small bodies in the solar system to better understand the genesis of the solar system and our Earth in particular. It is equipped with a 2Kx2K Andor CCD camera (20x20 arcmin) and 18 filters, among them a full set of HB comet filters (on loan from the Lowell Observatory) to measure the comets' gas and dust production rates. The IAU code is Z53 and 250 nights/yr are expected with an average seeing of 1.5". The new telescope, installed in a record time in spring 2016, allows now the scientists of the Belgian team to have access to the whole sky.

http://www.orca.ulg.ac.be/TRAPPIST/Trappist_main/News.html#new40

JWST Guaranteed-Time Observing Programs for Comets

NASA's James Webb Space Telescope (JWST) is on schedule to launch in Oct 2018, with the start of science operations in Spring 2019. An introduction to JWST can be found at jwst.stsci.edu/home and the telescope's potential for Solar System observations was summarized in a special issue of the Publications of the Astronomical Society of the Pacific.

As part of a Guaranteed-Time Observer program, "Solar System Observations with the James Webb Space Telescope", Heidi Hammel, JWST Interdisciplinary Scientist, has assembled a science team with a set of observing concepts for various targets to promote Solar System observations with the telescope. In order to provide the maximum benefit to the community, much of the data will have little or no proprietary period.

Three cometary observation concepts are planned:

  • ToO Observations of a Dynamically New Comet - Spectroscopy over the full wavelength range at multiple heliocentric distances corresponding to different snow lines driving comet activity.
  • Spectral Mapping of Comet 46P/Wirtanen - Spectroscopy over the full wavelength range and a 3"×3" field of view in May 2019. Proposed to demonstrate JWST's spectral mapping capabilities, and for scientific overlap with an observing campaign dedicated to this comet.
  • Direct Detection of Water in a Main-Belt Comet - Spectroscopy and wide-band imaging of comet 313P/Gibbs in Sep 2020. Proposed for the potential to be the first detection of gas in an MBC, and to inform observations of gas in any low-activity object.

The specifics for each concept will be refined and finalized in early 2017. Questions, comments, and input should be directed to the concept leads: M. Kelley for comets Wirtanen and Gibbs, S. Milam for the ToO comet.

Mike Kelley, Univ. Maryland
Stefanie Milam, NASA GSFC
Heidi Hammel, AURA

Post-doc position on observations of 67P

36 month contract at The Open University, UK.

Salary £29,301 to £38,183, depending on experience.

Ref: 12987.

Closing date: 9am GMT, Tuesday 29 November 2016

This part-ESA funded position will combine preparation of observational data on comet 67P/Churyumov-Gerasimenko for archiving at the ESA Planetary Science Archive, with research on cometary science. The research direction is flexible within the broad topic of comet science, and will depend on the interests of the successful candidate, but is expected to make use of (and/or build on) the same observations of 67P. Possible topics include the large-scale structure of the comet’s coma and tails, its composition, and/or comparison with other comets – in all cases, comparing between remote observation and Rosetta instrument results. The research could also involve further observations (based on new proposals) or work with Rosetta instrument teams, depending on the applicant’s interest and experience. There will be a roughly 50-50 split between research and functional duties. The duties encompass collation and documentation of data from various observatories, working with observers to ensure that data is properly reduced, and interaction with the ESA PSA to have it archived in a useful way alongside spacecraft data. For research topics related to observations of 67P, there will be a significant overlap between functional and research work.

You will be capable of independent research, with good organisational and interpersonal skills to work with observing teams around the world in preparing data products in a timely manner. You must have (or will shortly obtain) a PhD in Astronomy, Planetary Science or a related field.

For detailed information and how to apply go to www3.open.ac.uk/employment, call the Recruitment Co-ordinator on +44 (0)1908 653665 or email STEM-Recruitment@open.ac.uk quoting the reference number.

Contact Colin Snodgrass for more details: colin.snodgrass@open.ac.uk

Refereed Articles

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

Constraints on Comet 332P/Ikeya-Murakami

  • Hui, Man-To 1
  • Quan-Zhi Ye 2
  • Paul Wiegert 2,3
  1. EPSS, UCLA, USA
  2. Department of Physics and Astronomy, The University of Western Ontario, Canada
  3. Centre for Planetary Science and Exploration, UWO, Canada

Encke-type comet 332P/Ikeya-Murakami is experiencing cascading fragmentation events during its 2016 apparition. It is likely the first splitting Encke-type comet ever being observed. A nongravitational solution to the astrometry reveals a statistical detection of the radial and transverse nongravitational parameters, A1 = (1.54 ± 0.39) × 10−8 AU day−2, and A2 = (7.19 ± 1.92) × 10−9 AU day−2, respectively, which implies a nucleus erosion rate of (0.91 ± 0.17)% per orbital revolution. The mass-loss rate likely has to be supported by a much larger fraction of an active surface area than known cases of short-period comets; it may be relevant to the ongoing fragmentation. We failed to detect any serendipitous pre-discovery observations of the comet in archival data from major sky surveys, whereby we infer that 332P used to be largely inactive, and is perhaps among the few short-period comets which have been reactivated from weakly active or dormant states. We therefore constrain an upper limit to the nucleus size as 2.0 ± 0.2 km in radius. A search for small bodies in similar orbits to that of 332P reveals comet P/2010 B2 (WISE) as the best candidate. From an empirical generalised Jupiter-family (Encke-type included) comet population model, we estimate the likelihood of chance alignment of the 332P–P/2010 B2 pair to be 1 in 33, a small number indicative of a genetic linkage between the two comets on a statistical basis. The pair possibly originated from a common progenitor which underwent a disintegration event well before the twentieth century.

Astronomical Journal (In press)

arXiv: 1610.00877

Comets: Looking Ahead

  • A'Hearn, M. F. 1
  1. University of Maryland

Proposals to study comets often cite their importance in understanding where we came from, i.e., in learning how the solar system formed, how the planets formed, and how life arose on Earth. In order to address the role of comets in coming to this understanding, it is essential to ask ourselves what it is that we need to know about comets in order to understand the early solar system, i.e., what questions we should be asking about comets. For this paper we will focus on the the role of comets in learning how the solar system formed and how the planets formed. Since it was not a point of the Discussion Meeting, we will not consider the last part of where we came from, namely the role of comets in delivering water and organics to Earth, although the questions we do address here are clearly relevant to that question.We will also consider what progress has been achieved in recent years, particularly but not exclusively from Rosetta at comet 67P/Churyumov-Gerasimenko (hereafter 67P/CG), toward answering these key questions about comets. Finally, we will address the question of which future investigations are likely to be the most productive steps forward in improving our answers. It is, of course, impossible to address this topic comprehensively but much of the recent progress is covered by other papers in this volume so we point to those other articles to provide more comprehensive discussions.

Philosophical Transactions of the Royal Society A (In press)

Changes in the Physical Environment of the Inner Coma of 67P/Churyumov-Gerasimenko with Decreasing Heliocentric Distance

  • Bodewits, D 1
  • and 45 co-authorsNone
  1. University of Maryland in College Park

The Wide Angle Camera of the OSIRIS instrument on board the Rosetta spacecraft is equipped with several narrow-band filters that are centered on the emission lines and bands of various fragment species. These are used to determine the evolution of the production and spatial distribution of the gas in the inner coma of comet 67P with time and heliocentric distance, here between 2.6 and 1.3 au pre-perihelion. Our observations indicate that the emission observed in the OH, O I, CN, NH, and NH2 filters is mostly produced by dissociative electron impact excitation of different parent species. We conclude that CO2 rather than H2O is a significant source of the [O I] 630 nm emission. A strong plume-like feature observed in the CN and O I filters is present throughout our observations. This plume is not present in OH emission and indicates a local enhancement of the CO2/H2O ratio by as much as a factor of 3. We observed a sudden decrease in intensity levels after 2015 March, which we attribute to decreased electron temperatures in the first few kilometers above the surface of the nucleus.

Astronomical Journal (Published)

DOI: 10.3847/0004-6256/152/5/130 arXiv: 1607.05632

The perihelion activity of comet 67P/Churyumov-Gerasimenko as seen by robotic telescopes

  • Colin Snodgrass 1
  • Cyrielle Opitom 2
  • Miguel de Val-Borro 3,4
  • Emmanuel Jehin 2
  • Jean Manfroid 2
  • Tim Lister 5
  • Jon Marchant 6
  • Geraint H. Jones 7,8
  • Alan Fitzsimmons 9
  • Iain A. Steele 6
  • Robert J. Smith 6
  • Helen Jermak 6,10
  • Thomas Granzer 11
  • Karen J. Meech 12
  • Philippe Rousselot 13
  • Anny-Chantal Levasseur-Regourd 14
  1. School of Physical Sciences, The Open University, Walton Hall, Milton Keynes, MK7 6AA, UK
  2. Institut d'Astrophysique et de Géophysique, Université de Liège, allée du 6 Aout 17, B-4000 Liège, Belgium
  3. Department of Astrophysical Sciences, Princeton University, Princeton, NJ 08544, USA
  4. NASA Goddard Space Flight Center, Astrochemistry Laboratory, Code 691.0, Greenbelt, MD 20771, USA
  5. Las Cumbres Observatory Global Telescope Network, 6740 Cortona Drive Ste. 102, Goleta, CA 93117, USA
  6. Astrophysics Research Institute, Liverpool John Moores University, Liverpool, L3 5RF, UK
  7. Mullard Space Science Laboratory, University College London, Holmbury St. Mary, Dorking, Surrey RH5 6NT, UK
  8. The Centre for Planetary Sciences at UCL/Birkbeck, Gower Street, London WC1E 6BT, UK
  9. Astrophysics Research Centre, School of Mathematics and Physics, Queen's University Belfast, BT7 1NN, UK
  10. Physics Department, Lancaster University, Lancaster, LA1 4YB, UK
  11. Leibniz-Institut für Astrophysik Potsdam, An der Sternwarte 16, 14482 Potsdam, Germany
  12. Institute for Astronomy, 2680 Woodlawn Drive, Honolulu, HI 96822, USA
  13. University of Franche-Comté, Observatoire des Sciences de l'Univers THETA, Institut UTINAM - UMR CNRS 6213, BP 1615, 25010 Besançon Cedex,France
  14. LATMOS-IPSL; UPMC (Sorbonne Univ.), BC 102, 4 place Jussieu, 75005 Paris, France

Around the time of its perihelion passage the observability of 67P/Churyumov-Gerasimenko from Earth was limited to very short windows each morning from any given site, due to the low solar elongation of the comet. The peak in the comet's activity was therefore difficult to observe with conventionally scheduled telescopes, but was possible where service/queue scheduled mode was possible, and with robotic telescopes. We describe the robotic observations that allowed us to measure the total activity of the comet around perihelion, via photometry (dust) and spectroscopy (gas), and compare these results with the measurements at this time by Rosetta's instruments. The peak of activity occurred approximately two weeks after perihelion. The total brightness (dust) largely followed the predictions from Snodgrass et al. 2013, with no significant change in total activity levels from previous apparitions. The CN gas production rate matched previous orbits near perihelion, but appeared to be relatively low later in the year.

Monthly Notices of the Royal Astronomical Society (Published)

DOI: 10.1093/mnras/stw2300 NASA ADS: 2016MNRAS.tmp.1406S arXiv: 1610.06407

The Extremely Low Activity Comet 209P/LINEAR During Its Extraordinary Close Approach in 2014

  • Schleicher, D.G. 1
  • Knight, M.M. 1,2
  1. Lowell Observatory
  2. University of Maryland

We present results from our observing campaign of Comet 209P/LINEAR during its exceptionally close approach to Earth during 2014 May, the third smallest perigee of any comet in two centuries. These circumstances permitted us to pursue several studies of this intrinsically faint object, including measurements of gas and dust production rates, searching for coma morphology, and direct detection of the nucleus to measure its properties. Indeed, we successfully measured the lowest water production rates of an intact comet in over 35 years and a corresponding smallest active area, ∼0.007 km2. When combined with the nucleus size found from radar, this also yields the smallest active fraction for any comet, ∼0.024%. In all, this strongly suggests that 209P/LINEAR is on its way to becoming an inert object. The nucleus was detected but could not easily be disentangled from the inner coma due to seeing variations and changing spatial scales. Even so, we were able to measure a double-peaked lightcurve consistent with the shorter of two viable rotational periods found by Hergenrother. Radial profiles of the dust coma are quite steep, similar to that observed for some other very anemic comets, and suggest that vaporizing icy grains are present.

Astronomical Journal (Published)

DOI: 10.3847/0004-6256/152/4/89 NASA ADS: 2016AJ....152...89S arXiv: 1605.01705