Planetary Astronomy Late-morning Seminar for 2017-05-01

Series: Planetary Astronomy Late-morning Seminar
Date: Monday 1-May-2017
Time: 11:15-12:15
Location: CSS 1250
Speaker: Mike DiSanti (GSFC)
Title: High-resolution spectroscopy of Comet 45P/Honda-Mrkos-Pajdusakova with iSHELL at the IRTF: Secure detections of the under-studied hyper-volatiles CO and CH4 in a Jupiter-family comet

We observed Jupiter-family comet (JFC) 45P/Honda-Mrkos-Pajdusakova (hereafter 45P) shortly following its perihelion passage, using the new NASA-Infrared Telescope Facility 1-5 micron crossed-dispersed spectrograph (iSHELL) at high spectral resolving power (~4.5*10^4), and obtained the first molecular detections in a comet with this powerful instrument. We report water production, and production rates and abundance ratios relative to H2O on two dates (UT 7 and 8 January 2017) for eight trace parent molecules (i.e., native ices): CO, CH4, H2CO, CH3OH, HCN, NH3, C2H2, and C2H6. In all cases trace species were observed simultaneously with H2O and/or its proxy OH prompt emission. This allowed molecular abundance ratios to be established independent of systematic uncertainties such as potential temporal variations in gas production and differential slit losses among settings. Our observations revealed depleted abundances of CO and HCN, and enriched CH3OH relative to most comets measured to date. Most significantly, the highly favorable geocentric Doppler shift of 45P (approximately -35 km s‑1) permitted sensitive measures of CO and CH4. These hyper-volatiles are substantially under-characterized in JFCs, and therefore statistics on their abundances are severely lacking. Our measurements of 45P therefore provide a foundation from which to build a database of statistically meaningful abundances of CO and CH4 in JFCs. I will summarize our results for comet 45P, place these in the context of the continually growing taxonomy of parent volatile abundances among comets, and provide a summary of recent and planned future comet observations with iSHELL.

For further information contact PALS coordinator Dr. Matthew Knight at or (301)-405-2629.


Special accommodations for individuals with disabilities can be made by calling (301) 405-3001. It would be appreciated if we are notified at least one week in advance.


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