Cometary Science Newsletter

Issue
38
Month
May 2018
Editor
Michael S. P. Kelley (msk@astro.umd.edu)

LSST Solar System Science Collaboration

Over its 10 year lifespan, the Large Synoptic Survey Telescope (LSST) will catalog over 5 million Main Belt asteroids, almost 300,000 Jupiter Trojans, over 100,000 NEOs, over 40,000 KBOs, over 10,000 comets, and tens of interstellar objects. Many of these objects will receive hundreds of observations in multiple bandpasses. The LSST Solar System Science Collaboration (SSSC) is preparing methods and tools to analyze this data, as well as understand optimum survey strategies for discovering moving objects throughout the Solar System.

Learn more at http://www.lsstsssc.org, and read our science roadmap at https://arxiv.org/abs/1802.01783. Please consider joining the collaboration if you're an eligible researcher. If you have any questions, please contact the SSSC Co-Chairs, Meg Schwamb (mschwamb.astro@gmail.com) and David Trilling (David.Trilling@nau.edu).

Conference Announcements

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

Extended deadline for Physics of Comets After the Rosetta Mission

Dear Colleagues,

We invite you to register and submit an abstract of your contribution to the workshop “Physics of comets after the Rosetta mission: Unresolved problems” (September 5-7, 2018). The workshop will take place in Stará Lesná (Vysoké Tatry), Slovakia. The workshop will gather researchers studying different aspects of the physics of comets and discuss about the heritage of the Rosetta mission with special emphasis on the remaining issues, unresolved problems, and unexpected findings.

The planned registration and abstract submission deadline is extended to May 15, 2018. More information can be found on the workshop website:

https://www.astro.sk/AFTERROSETTA/

Refereed Articles

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

The Excited Spin State of 1I/2017 U1 ‘Oumuamua

  • Michael J. S. Belton 1, 2
  • Olivier R. Hainaut 3
  • Karen J. Meech 4
  • Beatrice E. A. Mueller 5
  • Jan T. Kleyna 4
  • Harold A. Weaver 6
  • Marc W. Buie 7
  • Michal Drahus 8
  • Piotr Guzik 8
  • Richard J. Wainscoat 4
  • Waclaw Waniak 8
  • Barbara Handzlik 8
  • Sebastian Kurowski 8
  • Siyi Xu 9
  • Scott S. Sheppard 10
  • Marco Micheli 11, 12
  • Harald Ebeling 4
  • Jacqueline V. Keane 4
  1. Belton Space Exploration Initiatives, LLC, 430 Randolph Way, Tucson AZ 85716 USA
  2. Kitt Peak National Observatory, Tucson, AZ 85719, USA
  3. European Southern Observatory, Karl-Schwarzschild-Strasse 2, D-85748 Garching bei Mu¨nchen, Germany
  4. Institute for Astronomy, 2680 Woodlawn Drive, Honolulu, HI 96822 USA
  5. Planetary Science Institute, 1700 East Fort Lowell, Suite 106, Tucson, AZ 85719-2395
  6. Johns Hopkins University, Bloomberg 145, APL 200-E210, 3400 N. Charles Street, Baltimore MD 21218 USA
  7. Southwest Research Institute, 1050 Walnut St., Suite 300, Boulder, CO 80302 USA
  8. Astronomical Observatory, Jagiellonian University, ul. Orla 171, 30-244, Krak´ow, Poland
  9. Gemini Observatory, 670 N. A’ohoku Place, Hilo HI, 96720 USA
  10. Carnegie Institution for Science, 5241 Broad Branch Rd. NW, Washington, DC 20015 USA
  11. ESA SSA-NEO Coordination Centre, Largo Galileo Galilei, 1, 00044 Frascati (RM), Italy
  12. INAF - Osservatorio Astronomico di Roma, Via Frascati, 33, 00040 Monte Porzio Catone (RM), Italy

We show that ‘Oumuamua's excited spin could be in a high-energy long axis mode (LAM) state, which implies that its shape could be far from the highly elongated shape found in previous studies. CLEAN and ANOVA algorithms are used to analyze ‘Oumuamua's lightcurve using 818 observations over 29.3 days. Two fundamental periodicities are found at frequencies (2.77 ± 0.11) and (6.42 ± 0.18) cycles/day, corresponding to (8.67 ± 0.34) hr and (3.74 ± 0.11) hr, respectively. The phased data show that the lightcurve does not repeat in a simple manner, but approximately shows a double minimum at 2.77 cycles/day and a single minimum at 6.42 cycles/day. ‘Oumuamua could be spinning in either the LAM or short axis mode (SAM). For both, the long axis precesses around the total angular momentum vector with an average period of (8.67 ± 0.34) hr. For the three LAMs we have found, the possible rotation periods around the long axis are 6.58, 13.15, or 54.48 hr, with 54.48 hr being the most likely. ‘Oumuamua may also be nutating with respective periods of half of these values. We have also found two possible SAM states where ‘Oumuamua oscillates around the long axis with possible periods at 13.15 and 54.48 hr. In this case any nutation occurs with the same periods. Determination of the spin state, the amplitude of the nutation, the direction of the total angular momentum vector (TAMV), and the average total spin period may be possible with a direct model fit to the lightcurve. We find that ‘Oumuamua is “cigar-shaped,” if close to its lowest rotational energy, and an extremely oblate spheroid if close to its highest energy state.

The Astrophysical Journal Letters (Published)

DOI: 10.3847/2041-8213/aab370 NASA ADS: 2018ApJ...856L..21B

Far-ultraviolet Spectroscopy of Recent Comets with the Cosmic Origins Spectrograph on the Hubble Space Telescope

  • Paul D. Feldman 1
  • Harold A. Weaver 2
  • Michael F. A'Hearn 3
  • Michael R. Combi 4
  • Neil Dello Russo 2
  1. Johns Hopkins University
  2. JHU/Applied Physics Laboratory
  3. University of Maryland
  4. University of Michigan

Since its launch in 1990, the Hubble Space Telescope (HST) has served as a platform with unique capabilities for remote observations of comets in the far-ultraviolet region of the spectrum. Successive generations of imagers and spectrographs have seen large advances in sensitivity and spectral resolution enabling observations of the diverse properties of a representative number of comets during the past 25 years. To date, four comets have been observed in the far-ultraviolet by the Cosmic Origins Spectrograph (COS), the last spectrograph to be installed in HST, in 2009: 103P/Hartley 2, C/2009 P1 (Garradd), C/2012 S1 (ISON), and C/2014 Q2 (Lovejoy). COS has unprecedented sensitivity, but limited spatial information in its 2.5 arcsec diameter circular aperture, and our objective was to determine the CO production rates from measurements of the CO Fourth Positive system in the spectral range of 1400 to 1700 Å. In the two brightest comets, nineteen bands of this system were clearly identified. The water production rates were derived from nearly concurrent observations of the OH (0,0) band at 3085 Å by the Space Telescope Imaging Spectrograph (STIS). The derived CO/H2O production rate ratio ranged from ~0.3% for Hartley 2 to ~22% for Garradd. In addition, strong partially resolved emission features due to multiplets of S I, centered at 1429 Å and 1479 Å, and of C I at 1561 Å and 1657 Å, were observed in all four comets. Weak emission from several lines of the H2 Lyman band system, excited by solar Lyman-alpha and Lyman-beta pumped fluorescence, were detected in comet Lovejoy.

Astronomical Journal (Published)

DOI: 10.3847/1538-3881/aab78a NASA ADS: 2018AJ....155..193F arXiv: 1803.07064

Hyperactivity and Dust Composition of Comet 103P/Hartley 2 During the EPOXI Encounter

  • Harker, D. E. 1
  • Woodward, C.E. 2
  • Kelley, M. S. P. 3
  • Wooden, D. H. 4
  1. University of California, San Diego
  2. University of Minnesota
  3. university of Maryland
  4. NASA Ames Research Center

Short-period comet 103P/Hartley 2 (103P) was the flyby target of the Deep Impact eXtended Investigation on 2010 November 4 UT. This comet has a small hyperactive nucleus, i.e., it has a high water production rate for its surface area. The underlying cause of the hyperactivity is unknown; the relative abundances of volatiles in the coma of 103P are not unusual. However, the dust properties of this comet have not been fully explored. We present four epochs of mid-infrared spectra and images of comet 103P observed from Gemini-South +T-ReCS on 2010 November 5, 7, 21 and December 13 UT, near and after the spacecraft encounter. Comet 103P exhibited a weak 10 μm emission feature ~1.14 ± 0.01 above the underlying local 10 μm continuum. Thermal dust grain modeling of the spectra shows the grain composition (mineralogy) was dominated by amorphous carbon and amorphous pyroxene with evidence for Mg-rich crystalline olivine. The grain size has a peak grain radius range of a peak ~0.5–0.9 μm. On average, the crystalline silicate mass fraction is ~0.24, fairly typical of other short-period comets. In contrast, the silicate-to-carbon ratio of ~0.48–0.64 is lower compared to other short-period comets, which indicates that the flux measured in the 10 μm region of 103P was dominated by amorphous carbon grains. We conclude that the hyperactivity in comet 103P is not revealing dust properties similar to the small grains seen with the Deep Impact experiment on comet 9P/Tempel 1 or from comet C/1995 O1 (Hale–Bopp).

Astronomical Journal (Published)

DOI: 10.3847/1538-3881/aab778 NASA ADS: 2018AJ....155..199H

Comet C/2011 W3 (Lovejoy) between 2 and 10 Solar Radii: Physical Parameters of the Comet and the Corona

  • Raymond, J.C. 1
  • Downs, C. 2
  • Knight, M.M. 3
  • Battams, K. 4
  • Giordano, S. 5
  • Rosati, R. 6
  1. Smithsonian Center for Astrophysics
  2. Predictive Sciences Inc
  3. University of Maryland
  4. US Naval Research Laboratory
  5. INAF-Osservatorio Astrofisico di Torino
  6. self

Comet C/2011 W3 (Lovejoy) is the first sungrazing comet in many years to survive perihelion passage. We report ultraviolet observations with the Ultraviolet Coronagraph Spectrometer (UVCS) spectrometer aboard the Solar and Heliospheric Observatory satellite at five heights as the comet approached the Sun. The brightest line, Lyα, shows dramatic variations in intensity, velocity centroid, and width during the observation at each height. We derive the outgassing rates and the abundances of N, O, and Si relative to H, and we estimate the effective diameter of the nucleus to be several hundred meters. We consider the effects of the large outgassing rate on the interaction between the cometary gas and the solar corona and find good qualitative agreement with the picture of a bow shock resulting from mass loading by cometary neutrals. We obtain estimates of the solar wind density, temperature, and speed, and compare them with predictions of a global magnetohydrodynamic simulation, finding qualitative agreement within our uncertainties. We also determine the sublimation rate of silicate dust in the comet’s tail by comparing the visible brightness from the Large Angle Spectroscopic Coronagraphs with the Si III intensity from UVCS. The sublimation rates lie between the predicted rates for olivines and pyroxenes, suggesting that the grains are composed of a mixture of those minerals.

The Astrophysical Journal (Published)

DOI: 10.3847/1538-4357/aabade

Spectroscopic observations of the comet 29P/Schwassmann-Wachmann 1 at the SOAR telescope

  • Ivanova, O.V. 1,2
  • Picazzio, E. 3
  • Luk'yanyk, I.V 4
  • Cavichia, O. 5
  • Andrievsky, S.M. 6,7
  1. Astronomical Institute of the Slovak Academy of Sciences, Slovak Republic
  2. Main Astronomical Observatory, National Academy of Sciences of Ukraine, Ukraine
  3. Universidade de São Paulo, Instituto de Astronomia, Geofsica e Ciências Atmosféricas, Brazil
  4. Astronomical Observatory, Taras Shevchenko National University of Kyiv, Ukraine
  5. Instituto de Física e Química, Universidade Federal de Itajubá, Brazil
  6. Department of Astronomy and Astronomical Observatory, Odessa National University, Ukraine
  7. GEPI, Observatoire de Paris, PSL Research University, France

Spectroscopic observations of comet 29P/Schwassmann-Wachmann 1 were carried out at the SOAR 4.1-meter telescope (Chile) on August 12, 2016, when its heliocentric distance was 5.9 au. The spectra revealed CO+ and N2+ emissions in the cometary coma. The [N2+]/[CO+] ratio within the projected slit seems to be 0.01. The mean value of the normalized spectral gradient is 12.69±0.06 for spectral range 3448–5260 Å.

Planetary and Space Science (In press)

DOI: 10.1016/j.pss.2018.04.003