Cometary Science Newsletter
- Issue
- 34
- Month
- January 2018
- Editor
- Michael S. P. Kelley (msk@astro.umd.edu)
Conference Announcements
Announcements for cometary conferences or workshops. Limited to 2000 characters.
First announcement of Rosetta Science Workshop in Rhodes, May 28- June 1 2018
The next Rosetta science workshop will be held in Rhodes, Greece from 28 May - June 1 2018. We aim to have a full week of science with an associated Science Working Team meeting. More information is available here: https://www.cosmos.esa.int/web/rosetta-swt-49/home. This first announcement aims to have you mark the date in your calendar. More information will appear on the web page in early 2018.
Refereed Articles
Abstracts of articles in press or recently published. Limited to 3000 characters.
FUV Spectral Signatures of Molecules and the Evolution of the Gaseous Coma of Comet 67P/Churyumov-Gerasimenko
- JHU
- UMd
- LATMOS
- SwRI
- Ball Aerospace
- JHU/APL
The Alice far-ultraviolet imaging spectrograph onboard Rosetta observed emissions from atomic and molecular species from within the coma of comet 67P/Churyumov-Gerasimenko during the entire escort phase of the mission from 2014 August to 2016 September. The initial observations showed that emissions of atomic hydrogen and oxygen close to the surface were produced by energetic electron impact dissociation of H2O. Following delivery of the lander, Philae, on 2014 November 12, the trajectory of Rosetta shifted to near-terminator orbits that allowed for these emissions to be observed against the shadowed nucleus that, together with the compositional heterogeneity, enabled us to identify unique spectral signatures of dissociative electron impact excitation of H2O, CO2, and O2. CO emissions were found to be due to both electron and photoexcitation processes. Thus we are able, from far-ultraviolet spectroscopy, to qualitatively study the evolution of the primary molecular constituents of the gaseous coma from start to finish of the escort phase. Our results show asymmetric outgassing of H2O and CO2 about perihelion, H2O dominant before and CO2 dominant after, consistent with the results from both the in situ and other remote sensing instruments on Rosetta.
Astronomical Journal (In press)
DOI: 10.3847/1538-3881/aa9bf2 arXiv: 1711.0738
Hyper-volatiles in a Jupiter-family comet: Observations of 45P/Honda-Mrkos-Pajdusáková using iSHELL at the NASA-IRTF
- Solar System Exploration Division, Planetary Systems Laboratory Code 693, NASA-Goddard Space Flight Center, Greenbelt, MD, USA
- Goddard Center for Astrobiology, NASA-Goddard Space Flight Center, Greenbelt, MD, USA
- Department of Physics and Astronomy, American University, Washington, DC, USA
- The Johns Hopkins University Applied Physics Laboratory, Laurel, MD 20723-6099, USA
- Department of Physics and Astronomy, University of Missouri-St. Louis, Saint Louis, MO, USA
- Universities Space Research Association/NASA Postdoctoral Program, Columbia, MD, USA
- Koyama Astronomical Observatory, Kyoto Sangyo University Motoyama, Kamingamo, Kita-ku, Kyoto 603-8555, Japan
- Department of Astronomy, University of Maryland, College Park, MD, USA
We used the new high spectral resolution cross-dispersed facility spectrograph, iSHELL, at the NASA Infrared Telescope Facility on Maunakea, HI, to observe Jupiter-family comet (JFC) 45P/Honda–Mrkos–Pajdušáková. We report water production rates, as well as production rates and abundance ratios relative to H2O, for eight trace parent molecules (native ices), CO, CH4, H2CO, CH3OH, HCN, NH3, C2H2, and C2H6, on 2 days spanning UT 2017 January 6/7 and 7/8, shortly following perihelion. Trace species were measured simultaneously with H2O and/or OH prompt emission, a proxy for H2O production, thereby providing a robust and consistent means of establishing the native ice composition of 45P. Its favorable geocentric radial velocity (approximately −35 km s−1) permitted sensitive measures of the “hypervolatiles” CO and CH4, which are substantially undercharacterized in JFCs. Our results represent the most precise ground-based measures of CO and CH4 to date in a JFC, providing a foundation for building meaningful statistics regarding their abundances. The abundance ratio for CH4 in 45P (0.79% ± 0.06% relative to H2O) was consistent with its median value as measured among Oort Cloud comets, whereas CO (0.60%±0.04%) was strongly depleted. Compared with all measured comets, HCN (0.049%±0.012%) was strongly depleted, CH3OH (3.6%±0.3%) was enriched, and the remaining species were consistent with their respective median abundances. The volatile composition measured for 45P could indicate processing of ices prior to their incorporation into its nucleus. Spatial analysis of emissions suggests enhanced release of more volatile species into the sunward-facing hemisphere of the coma.
Astronomical Journal (Published)
DOI: 10.3847/1538-3881/aa8639 NASA ADS: 2017AJ....154..246D
On the rotation period and shape of the hyperbolic asteroid 1I/‘Oumuamua (2017 U1) from its lightcurve
- University of Maryland
We observed the newly discovered hyperbolic minor planet 1I/‘Oumuamua (2017 U1) on 2017 October 30 with Lowell Observatory's 4.3-m Discovery Channel Telescope. From these observations, we derived a partial lightcurve with peak-to-trough amplitude of at least 1.2 mag. This lightcurve segment rules out rotation periods less than 3 hr and suggests that the period is at least 5 hr. On the assumption that the variability is due to a changing cross section, the axial ratio is at least 3:1. We saw no evidence for a coma or tail in either individual images or in a stacked image having an equivalent exposure time of 9000 s.
The Astrophysical Journal Letters (Published)
DOI: 10.3847/2041-8213/aa9d81 NASA ADS: 2017arXiv171101402K arXiv: 1711.01402