Cometary Science Newsletter

Issue
6
Month
September 2015
Editor
Michael S. P. Kelley (msk@astro.umd.edu)

Refereed Articles

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

The Volatile Composition of Comet C/2003 K4 (LINEAR) at Near-IR Wavelengths—Comparisons with Results from the Nançay Radio Telescope and from the Odin, Spitzer, and SOHO Space Observatories

  • L. Paganini 1,2
  • M. J. Mumma 1
  • G. L. Villanueva 1,2
  • M. A. DiSanti 1
  • B. P. Bonev 1,2
  1. Goddard Center for Astrobiology, NASA GSFC, MS 690, Greenbelt, MD 20771, USA
  2. Department of Physics, Catholic University of America, Washington, DC 20064, USA

We observed comet C/2003 K4 (LINEAR) using NIRSPEC at the Keck Observatory on UT 2004 November 28, when the comet was at 1.28 AU from the Sun (post-perihelion) and 1.38 AU from Earth. We detected six gaseous species (H2O, OH*, C2H6, CH3OH, CH4, and HCN) and obtained upper limits for three others (H2CO, C2H2, and NH3). Our results indicate a water production rate of (1.72 ± 0.18) × 1029 molecules s−1, in reasonable agreement with production rates from SOHO (on the same day), Odin (one day earlier), and Nançay (about two weeks earlier). We also report abundances (relative to water) for seven trace species: CH3OH (~1.8%), CH4 (~0.9%), and C2H6 (~0.4%) that were consistent with mean values among Oort cloud (OC) comets, while NH3 (<0.55%), HCN (~0.07%), H2CO (<0.07%), and C2H2 (<0.04%) were "lower" than the mean values in other OC comets. We extracted inner-coma rotational temperatures for four species (H2O, C2H6, CH3OH, and CH4), all of which are consistent with 70 K (within 1σ). The extracted ortho-para ratio for water was 3.0 ± 0.15, corresponding to spin temperatures larger than 39 K (at the 1σ level) and agreeing with those obtained with the Spitzer Space Telescope at the 2σ level.

The Astrophysical Journal (Published)

DOI: 10.1088/0004-637X/808/1/1 NASA ADS: 2015ApJ...808....1P

Asteroids and Comets

  • Yanga R. Fernandez 1
  • Jian-Yang Li 2
  • Ellen S. Howell 3
  • Laura M. Woodney 4
  1. University of Central Florida, U.S.A.
  2. Planetary Science Institute, U.S.A.
  3. Arecibo Observatory/USRA, U.S.A.
  4. California State University – San Bernardino, U.S.A.

Asteroids and comets are remnants from the era of Solar System formation over 4.5 billion years ago, and therefore allow us to address two fundamental questions in astronomy: what was the nature of our protoplanetary disk, and how did the process of planetary accretion occur? The objects we see today have suffered many geophysically-relevant processes in the intervening eons that have altered their surfaces, interiors, and compositions. In this chapter we review our understanding of the origins and evolution of these bodies, discuss the wealth of science returned from spacecraft missions, and motivate important questions to be addressed in the future.

Treatise on Geophysics, 2nd ed., Vol. 10 (Published)

DOI: 10.1016/B978-0-444-53802-4.00184-6 arXiv: 1507.06578

CometCIEF: A web-based image enhancement facility to digitally enhance images of cometary comae

  • Martin, M.P. 1,2
  • Samarasinha, N. 1
  • Larson, S. 2
  1. Planetary Science Institute, USA.
  2. University of Arizona, USA.

We present details of an online web facility for enhancing coma images of comets. This facility, the Cometary Coma Image Enhancement Facility (CometCIEF), allows a user to enhance FITS images using five advanced image enhancement techniques which were not previously available as an open source. The resultant enhanced image as well as intermediate images produced during the enhancement process can then be downloaded as FITS images. We provide additional documentation and source codes for the user to download at the Facility, available at http://www.psi.edu/research/cometimen.

Planetary and Space Science (In press)

DOI: 10.1016/j.pss.2015.06.019

Evolution of the ion environment of comet 67P/Churyumov-Gerasimenko - Observations between 3.6 and 2.0 AU

  • Hans Nilsson 1
  • and 30 co-authorsNone
  1. Swedish Institute of Space Physics, Box 812, 981 28 Kiruna, Sweden

Context. The Rosetta spacecraft is escorting comet 67P/Churyumov-Gerasimenko from a heliocentric distance of >3.6 AU, where the comet activity was low, until perihelion at 1.24 AU. Initially, the solar wind permeates the thin comet atmosphere formed from sublimation.

Aims. Using the Rosetta Plasma Consortium Ion Composition Analyzer (RPC-ICA), we study the gradual evolution of the comet ion environment, from the first detectable traces of water ions to the stage where cometary water ions accelerated to about 1 keV energy are abundant. We compare ion fluxes of solar wind and cometary origin.

Methods. RPC-ICA is an ion mass spectrometer measuring ions of solar wind and cometary origins in the 10 eV–40 keV energy range.

Results. We show how the flux of accelerated water ions with energies above 120 eV increases between 3.6 and 2.0 AU. The 24 h average increases by 4 orders of magnitude, mainly because high-flux periods become more common. The water ion energy spectra also become broader with time. This may indicate a larger and more uniform source region. At 2.0 AU the accelerated water ion flux is frequently of the same order as the solar wind proton flux. Water ions of 120 eV–few keV energy may thus constitute a significant part of the ions sputtering the nucleus surface. The ion density and mass in the comet vicinity is dominated by ions of cometary origin. The solar wind is deflected and the energy spectra broadened compared to an undisturbed solar wind.

Conclusions. The flux of accelerated water ions moving from the upstream direction back toward the nucleus is a strongly nonlinear function of the heliocentric distance.

Astronomy and Astrophysics (In press)

DOI: 10.1051/0004-6361/201526142

SOFIA Infrared Spectrophotometry of Comet C/2012 K1 (Pan-STARRS)

  • Charles E. Woodward 1
  • Michael S. P. Kelley 2
  • David E. Harker 3
  • Erin L. Ryan 2
  • Diane H. Wooden 4
  • Michael L. Sitko 5
  • Ray W. Russell 6
  • William T. Reach 7
  • Imke de Pater 8
  • Ludmilla Kolokolova 2
  • Robert D. Gehrz 1
  1. Minnesota Institute for Astrophysics, University of Minnesota
  2. University of Maryland, Department of Astronomy
  3. University of California, San Diego, Center for Astrophysics & Space Sciences
  4. NASA Ames Research Center
  5. Department of Physics, University of Cincinnati
  6. The Aerospace Corporation
  7. USRA-SOFIA Science Center, NASA Ames Research Center
  8. Astronomy Department, University of California, Berkeley

We present pre-perihelion infrared 8–31 μm spectrophotometric and imaging observations of comet C/2012 K1 (Pan-STARRS), a dynamically new Oort Cloud comet, conducted with NASA's Stratospheric Observatory for Infrared Astronomy facility (+FORCAST) in 2014 June. As a “new” comet (first inner solar system passage), the coma grain population may be extremely pristine, unencumbered by a rime and insufficiently irradiated by the Sun to carbonize its surface organics. The comet exhibited a weak 10 μm silicate feature ≃1.18 ± 0.03 above the underlying best-fit 215.32 ± 0.95 K continuum blackbody. Thermal modeling of the observed spectral energy distribution indicates that the coma grains are fractally solid with a porosity factor D = 3 and the peak in the grain size distribution, apeak = 0.6 μm, large. The sub-micron coma grains are dominated by amorphous carbon, with a silicate-to-carbon ratio of 0.80+0.25-0.20. The silicate crystalline mass fraction is 0.20+0.30-0.10, similar to with other dynamically new comets exhibiting weak 10 μm silicate features. The bolometric dust albedo of the coma dust is 0.14 ± 0.01 at a phase angle of 34.°76, and the average dust production rate, corrected to zero phase, at the epoch of our observations was Afρ ≃ 5340 cm.

Astrophysical Journal (Published)

DOI: 10.1088/0004-637X/809/2/181 NASA ADS: 2015ApJ...809..181W arXiv: 1508.00288