En route to destruction: The evolution in composition of ICES in comet D/2012 S1 (ISON) between 1.2 and 0.34 AU from the Sun as revealed at infrared wavelengths

Journal Article · Sun Mar 20 04:00:00 EDT 2016 · Astrophysical Journal

DOI:https://doi.org/10.3847/0004-637X/820/1/34· OSTI ID:22890074

DiSanti, M. A.; Bonev, B. P.; Gibb, E. L.; Paganini, L.; Villanueva, G. L.; Mumma, M. J.; Blake, G. A. ^[1]; Keane, J. V.; Meech, K. J. ^[2]; Russo, N. Dello; Vervack, Jr., R. J. ^[3]

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1. Goddard Center for Astrobiology, NASA Goddard Space Flight Center, Greenbelt, MD (United States)
2. Institute for Astronomy, University of Hawaii at Manoa, Honolulu, HI (United States)
3. The Johns Hopkins University Applied Physics Laboratory, Laurel, MD 20723-6099 (United States)

We report production rates for H{sub 2}O and eight trace molecules (CO, C{sub 2}H{sub 6}, CH{sub 4}, CH{sub 3}OH, NH{sub 3}, H{sub 2}CO, HCN, C{sub 2}H{sub 2}) in the dynamically new, Sun-grazing Comet C/2012 S1 (ISON), using high-resolution spectroscopy at Keck II and the NASA IRTF on 10 pre-perihelion dates encompassing heliocentric distances R{sub h} = 1.21–0.34 AU. Measured water production rates spanned two orders of magnitude, consistent with a long-term heliocentric power law Q(H{sub 2}O) ∝R{sub h}{sup (−3.1±0.1)}. Abundance ratios for CO, C{sub 2}H{sub 6}, and CH{sub 4} with respect to H{sub 2}O remained constant with R{sub h} and below their corresponding mean values measured among a dominant sample of Oort Cloud comets. CH{sub 3}OH was also depleted for R{sub h} > 0.5 AU, but was closer to its mean value for R{sub h} ≤ 0.5 AU. The remaining four molecules exhibited higher abundance ratios within 0.5 AU: for R{sub h} > 0.8 AU, NH{sub 3} and C{sub 2}H{sub 2} were consistent with their mean values while H{sub 2}CO and HCN were depleted. For R{sub h} < 0.5 AU, all four were enriched, with NH{sub 3}, H{sub 2}CO, and HCN increasing most. Spatial profiles of gas emission in ISON consistently peaked sunward of the dust continuum, which was asymmetric antisunward and remained singly peaked for all observations. NH{sub 3} within 0.5 AU showed a broad spatial distribution, possibly indicating its release in the coma provided that optical depth effects were unimportant. The column abundance ratio NH{sub 2}/H{sub 2}O at 0.83 AU was close to the “typical” NH/OH from optical wavelengths, but was higher within 0.5 AU. Establishing its production rate and testing its parentage (e.g., NH{sub 3}) require modeling of coma outflow.

• OSTI ID: 22890074
• Journal Information: Astrophysical Journal, Journal Name: Astrophysical Journal Journal Issue: 1 Vol. 820; ISSN ASJOAB; ISSN 0004-637X
• Country of Publication: United Kingdom
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
AMMONIA
ASYMMETRY
CARBON MONOXIDE
COMETS
COMPUTERIZED SIMULATION
COSMIC DUST
COSMIC GASES
ELEMENT ABUNDANCE
EMISSION
ETHANE
EVOLUTION
HYDROCYANIC ACID
METHANE
METHANOL
MOLECULES
RESOLUTION
SPATIAL DISTRIBUTION
SUN
TESTING
WATER