Detection of Abundant Ethane and Methane, Along with Carbon Monoxide and Water, in Comet C/1996 B2 Hyakutake: Evidence for Interstellar Origin

The saturated hydrocarbons ethane (C2H6) and methane (CH4) along with carbon monoxide (CO) and water (H2O) were detected in comet C/1996 B2 Hyakutake with the use of high-resolution infrared spectroscopy at the NASA Infrared Telescope Facility on Mauna Kea, Hawaii. The inferred production rates of molecular gases from the icy, cometary nucleus (in molecules per second) are 6.4 × 1026 for C2H6, 1.2 × 1027 for CH4, 9.8 × 1027 for CO, and 1.7 × 1029 for H2O. An abundance of C2H6 comparable to that of CH4 implies that ices in C/1996 B2 Hyakutake did not originate in a thermochemically equilibrated region of the solar nebula. The abundances are consistent with a kinetically controlled production process, but production of C2H6 by gas-phase ion molecule reactions in the natal cloud core is energetically forbidden. The high C2H6/CH4 ratio is consistent with production of C2H6 in icy grain mantles in the natal cloud, either by photolysis of CH4-rich ice or by hydrogen-addition reactions to acetylene condensed from the gas phase.

[1]  K. Hiraoka,et al.  Formation of formaldehyde and methanol from the reactions of H atoms with solid CO at 10–20 K , 1994 .

[2]  J. Davies,et al.  Observations of submillimetre lines of CH3OH, HCN, and H2CO in comet P/Swift-Tuttle with the James Clerk Maxwell Telescope , 1994 .

[3]  M. Moore,et al.  Far-infrared spectral studies of phase changes in water ice induced by proton irradiation , 1992 .

[4]  N. L. Allinger,et al.  Intensities of infrared bands in molecular mechanics (MM3) , 1992 .

[5]  V. M. Devi,et al.  THE HITRAN MOLECULAR DATABASE: EDITIONS OF 1991 AND 1992 , 1992 .

[6]  J. Lacy,et al.  A possible detection of infrared emission from carbon monoxide in Comet Austin (1989c 1) , 1992 .

[7]  D. Reuter,et al.  A tentative identification of methanol as the progenitor of the 3.52-μm emission feature in several comets , 1991 .

[8]  Neal J. Evans,et al.  Discovery of interstellar methane - Observations of gaseous and solid CH4 absorption toward young stars in molecular clouds , 1991 .

[9]  H. Weaver,et al.  A sensitive upper limit on the methane abundance in Comet Levy (1990c) , 1991 .

[10]  J. Greenberg,et al.  Explosive desorption of icy grain mantles in dense clouds , 1991 .

[11]  D. Despois,et al.  Microwave detection of hydrogen sulphide and methanol in comet Austin (1989c1) , 1991, Nature.

[12]  W. Huebner,et al.  Distributed coma sources and the CH4/CO ratio in Comet Halley , 1990 .

[13]  D. Reuter,et al.  On the identification of formaldehyde in Halley's comet , 1989 .

[14]  H. Weaver,et al.  Airborne infrared spectroscopy of Comet Wilson (1986l) and comparisons with Comet Halley , 1989 .

[15]  H. Shibai,et al.  Infrared spectroscopic observation of methane in Comet P/Halley , 1988 .

[16]  Michel Combes,et al.  The 2.5-12 μm spectrum of comet halley from the IKS-VEGA experiment , 1988 .

[17]  Scott A. Sandford,et al.  Photochemical and thermal evolution of interstellar/precometary ice analogs , 1988 .

[18]  W. Ip,et al.  Evidence for methane and ammonia in the coma of comet P/Halley. , 1987, Astronomy & Astrophysics.

[19]  H. Larson,et al.  Search for methane in Comet Halley , 1987 .

[20]  F. Schloerb,et al.  HCN production from comet Halley , 1986 .

[21]  H. Weaver,et al.  Detection of Water Vapor in Halley's Comet , 1986, Science.

[22]  H. Weaver,et al.  Vibrational and rotational excitation of CO in comets Nonequilibrium calculations , 1984 .

[23]  H. Weaver,et al.  Erratum - Infrared Molecular Emissions from Comets , 1984 .

[24]  N. Blair,et al.  Carbon isotope composition of low molecular weight hydrocarbons and monocarboxylic acids from Murchison meteorite , 1984, Nature.

[25]  H. Weaver,et al.  Infrared molecular emissions from comets , 1984 .

[26]  T. Encrenaz,et al.  Infrared fluorescence of molecules in comets - The general synthetic spectrum , 1983 .

[27]  E. Herbst,et al.  Laboratory measurements of ion-molecule reactions pertaining to interstellar hydrocarbon synthesis , 1983 .

[28]  J. Lawless,et al.  Quantification of monocarboxylic acids in the Murchison carbonaceous meteorite , 1979, Nature.

[29]  M. O. Dayhoff,et al.  Thermodynamic Equilibrium and the Inorganic Origin of Organic Compounds , 1966, Science.

[30]  J. Hillman,et al.  Vacuum-Ultraviolet Photochemistry. II. Solid and Gas-Phase Photolysis of Methane-Water Systems , 1965 .

[31]  E. Anders,et al.  Organic Compounds in Carbonaceous Chondrites. , 1965, Science.

[32]  D. Krankowsky,et al.  The extended formaldehyde source in comet P/Halley , 1993 .

[33]  A. Goldman,et al.  Ethane 3 μm spectral clusters of atmospheric interest , 1989 .

[34]  I. Pater,et al.  Radio Detection of Formaldehyde Emission from Comet Halley , 1989 .

[35]  J. Hoffman,et al.  Expansion velocity and temperatures of gas and ions measured in the coma of comet P/Halley , 1988 .

[36]  J. Crovisier,et al.  The 2.7 μm water band of comet P/Halley: interpretation of observations by an excitation model , 1988 .

[37]  J. Hoffman,et al.  The CO and N2 abundance in comet P/Halley , 1988 .

[38]  Walter F. Huebner,et al.  Cometary MHD and chemistry , 1988 .