Detection of acetylene in the infrared spectrum of comet Hyakutake

COMETS are rich in volatile materials, of which roughly 80% (by number) are water molecules1. Considerable progress2–4 is being made in identifying the other volatile species, the abundances of which should enable us to determine whether comets formed primarily from ice-covered interstellar grains5, or from material that was chemically processed in the early solar nebula6,7. Here we report the detection of acetylene (C2H2) in the infrared spectrum of comet C/1996 B2 (Hyakutake). The estimated abundance is 0.3–0.9%, relative to water, which is comparable to the predicted solid-phase abundance in cold interstellar clouds. This suggests that the volatiles in comet Hyakotake may have come from ice-covered interstellar grains, rather than material processed in the accretion disk out of which the Solar System formed.

[1]  E. Herbst,et al.  Three-phase chemical models of dense interstellar clouds: gas, dust particle mantles and dust particle surfaces , 1993 .

[2]  R. L. Newburn,et al.  Comets in the post-Halley era , 1991 .

[3]  D. Crisp,et al.  Ground‐based near‐infrared observations of the Venus nightside: The thermal structure and water abundance near the surface , 1996 .

[4]  W. Huebner,et al.  Solar photo rates for planetary atmospheres and atmospheric pollutants , 1984 .

[5]  J. Crovisier,et al.  The nature of the 2.8-micron emission feature in cometary spectra , 1989 .

[6]  R. Prinn,et al.  Kinetic inhibition of CO and N2 reduction in circumplanetary nebulae - Implications for satellite composition , 1981 .

[7]  W. Jackson.  The photochemical formation of cometary radicals , 1976 .

[8]  Alan T. Tokunaga,et al.  CSHELL: a high spectral resolution 1-5-μm cryogenic echelle spectrograph for the IRTF , 1993, Defense, Security, and Sensing.

[9]  Michael F. A'Hearn,et al.  The fluorescence of cometary OH , 1988 .

[10]  J. Hoffman,et al.  In situ gas and ion measurements at comet Halley , 1986 .

[11]  Tetsuo Yamamoto.  Chemical Theories on the Origin of Comets , 1989 .

[12]  C. Kaminski,et al.  Detection of Abundant Ethane and Methane, Along with Carbon Monoxide and Water, in Comet C/1996 B2 Hyakutake: Evidence for Interstellar Origin , 1996, Science.

[13]  Neal J. Evans,et al.  Observation of infrared and radio lines of molecules toward GL 2591 and comparison to physical and chemical models , 1995 .

[14]  P. McCarthy,et al.  C2 in Comet Halley: evidence for its being third generation and resolution of the vibrational population discrepancy , 1988 .

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

[16]  Donald N. B. Hall,et al.  Design for a 1--5-um cryogenic echelle spectrograph for the NASA IRTF , 1990, Astronomical Telescopes and Instrumentation.

[17]  D. Hurtmans,et al.  The ν3 Fundamental in C2H2 , 1993 .

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

[19]  Robert E. Johnson,et al.  Irradiation Effects on Comets and Cometary Debris , 1989 .

[20]  J. Lunine,et al.  Protostars and planets III , 1993 .

[21]  J. Crovisier.  Rotational and vibrational synthetic spectra of linear parent molecules in comets , 1987 .