Search for CO gas in Pluto, Centaurs and Kuiper Belt objects at radio wavelengths

We have searched for several rotational lines of CO in the Pluto-Charon system, Centaurs (Chiron, Pholus, Nessus, Asbolus, Chariklo and 1998 SG35) and Kuiper Belt objects (1994 TB, 1996 TL66, 1996 TO66, 1996 TP66 and 1998 WH4). The observations were performed with the 30 m telescope of the Institut de Radioastronomie Millimetrique for Pluto/Charon, and with the James Clerk Maxwell Telescope and Caltech Submillimeter Observatory for Centaurs and Kuiper Belt objects. A tentative 4.5-σ J(2-1) CO line is present in the Pluto/Charon spectrum, which requires further confirmation. Assuming that Charon does not contribute to the CO emission, an upper limit of 1.2% and 7% is obtained for the CO/N_2 mixing ratio in Pluto's atmosphere, using the atmospheric thermal structure derived from the Stansberry et al. (1994, Icarus 111, 503) and Strobel et al. (1996, Icarus 120, 266) models, respectively. These upper limits are more constraining (by more than a factor of 6) than the upper limits reported by Young et al. (2001, Icarus, in press) from near-IR spectroscopy. None of the Centaurs or Kuiper Belt objects (KBO) were detected in CO. The CO production rate upper limit obtained for Chiron (3-5 x 10^(27) mol s^(-1)) over 1998-2000 years is a factor of 10 lower than the CO production rate derived from the marginal CO detection obtained in June 1995 by Womack & Stern ([CITE], Astron. Vestnik 33, 216), using same modelling of CO emission. Upper limits obtained for other Centaurs are typically ~10^(28) mol s^(-1), and between 1 and 5 x 10^(28) mol s^(-1) for the best observed KBOs. The comparison between these upper limits and the CO outgassing rates of comet C/1995 O1 (Hale-Bopp) measured at large distances from the Sun shows that Centaurs and KBOs underwent significant CO-devolatilization since their formation.

[1]  Alan T. Tokunaga,et al.  Detection of Gaseous Methane on Pluto , 1997 .

[2]  R. Hodges.  Monte Carlo simulation of nonadiabatic expansion in cometry atmospheres: Halley , 1990 .

[3]  T. Owen,et al.  The Composition of Centaur 5145 Pholus , 1998 .

[4]  D. Jewitt,et al.  Optical and Infrared Reflectance Spectrum of Kuiper Belt Object 1996 TL66 , 1998 .

[5]  A. Coradini,et al.  Chiron Activity and Thermal Evolution , 2000 .

[6]  J. Crifo,et al.  The Dependence of the Circumnuclear Coma Structure on the Properties of the Nucleus: III. First Modeling of a CO-Dominated Coma, with Application to Comets 46 P/Wirtanen and 29 P/Schwassmann–Wachmann I☆ , 1999 .

[7]  E. Lellouch,et al.  Carbon Monoxide Outgassing from Comet P/Schwassmann-Wachmann 1 , 1995 .

[8]  J. Greenberg,et al.  Thermal history of comets during residence in the Oort Cloud: Effect of radiogenic heating in combination with the very low thermal conductivity of amorphous ice , 1993 .

[9]  C. H. Ford,et al.  Stellar Occultation by 2060 Chiron , 1996 .

[10]  D. Prialnik,et al.  Modelling the activity of 2060 Chiron , 1995 .

[11]  C. Koresko,et al.  Detection of Water Ice on the Centaur 1997 CU26 , 1998 .

[12]  F. Bertoldi,et al.  Size determination of the Centaur Chariklo from millimeter-wavelength bolometer observations , 2000, astro-ph/0012370.

[13]  S. Tegler,et al.  Extremely red Kuiper-belt objects in near-circular orbits beyond 40  AU , 2000, Nature.

[14]  L A Young,et al.  Surface Ices and the Atmospheric Composition of Pluto , 1993, Science.

[15]  David J. Tholen,et al.  The Orbit of Charon , 1997 .

[16]  G. R. Gladstone,et al.  The Pluto-Charon system: The escape of charon's primordial atmosphere , 1988 .

[17]  G. Blake,et al.  Near-Infrared Spectroscopy of the Bright Kuiper Belt Object 2000 EB173 , 2000 .

[18]  Peter J. Barnes.  A search for CO emission from the Pluto-Charon system , 1993 .

[19]  Robert H. Brown,et al.  Water Ice on Kuiper Belt Object 1996 TO66 , 1999 .

[20]  Marc W. Buie,et al.  Albedo maps of Pluto and Charon: Initial mutual event results , 1992 .

[21]  P. Kalas,et al.  Thermal Observations of Centaur 1997 CU26 , 1998 .

[22]  R. H. Brown,et al.  Compositional Variation on the Surface of Centaur 8405 Asbolus , 2000 .

[23]  Harold F. Levison,et al.  From the Kuiper Belt to Jupiter-Family Comets: The Spatial Distribution of Ecliptic Comets☆ , 1997 .

[24]  William B. Hubbard,et al.  Mirages and the Nature of Pluto's Atmosphere , 1994 .

[25]  D. Prialnik,et al.  Radioactive Heating of Porous Comet Nuclei , 1995 .

[26]  Water Ice in 2060 Chiron and Its Implications for Centaurs and Kuiper Belt Objects. , 2000, The Astrophysical journal.

[27]  Michael E. Brown,et al.  Near-Infrared Spectroscopy of Centaurs and Irregular Satellites , 2000 .

[28]  T. Owen,et al.  Composition, Physical State, and Distribution of Ices at the Surface of Triton , 1999 .

[29]  A. Boss,et al.  Protostars and Planets VI , 2000 .

[30]  L. Young,et al.  Limits on the radius and a possible atmosphere of Charon from its 1980 stellar occultation , 1991 .

[31]  A. Casati,et al.  Photometric monitoring of 2060 Chiron's brightness at perihelion , 1997 .

[32]  James L. Elliot,et al.  Pluto's Radius and Atmosphere: Results from the Entire 9 June 1988 Occultation Data Set , 1993 .

[33]  R. Moreno,et al.  Spectroscopic Monitoring of Comet C/1996 B2 (Hyakutake) with the JCMT and IRAM Radio Telescopes , 1999 .

[34]  S. Tegler,et al.  Two distinct populations of Kuiper-belt objects , 1998, Nature.

[35]  David Jewitt,et al.  Color Diversity Among the Centaurs and Kuiper Belt Objects , 1996 .

[36]  J. Colmont,et al.  Self, nitrogen and oxygen broadening of the 115-GHz line of carbon monoxide , 1986 .

[37]  M. A’Hearn,et al.  (2060) Chiron: Evidence for Activity near Aphelion , 2001 .

[38]  N. Mcbride,et al.  Optical and infrared observations of the Centaur 1997 CU26 , 1999 .

[39]  G. Rieke,et al.  The color temperature of (2060) Chiron: A warm and small nucleus , 1994 .

[40]  A. Coradini,et al.  Thermal Evolution and Differentiation of Edgeworth-Kuiper Belt Objects , 2001 .

[41]  A. Coradini,et al.  Thermal Evolution of the Centaur Object 5145 Pholus , 2000 .

[42]  D. Jewitt,et al.  Coma formation driven by carbon monoxide release from comet Schwassmann–Wachmann 1 , 1994, Nature.

[43]  Emmanuel Lellouch,et al.  Search for Variations in Pluto's Millimeter-Wave Emission , 2000 .

[44]  Emmanuel Lellouch,et al.  The Thermal Structure of Pluto's Atmosphere: Clear vs Hazy Models , 1994 .

[45]  Dominic J. Benford,et al.  Long-term Evolution of the Outgassing of Comet Hale-Bopp From Radio Observations , 1997 .

[46]  Xun Zhu,et al.  On the vertical thermal structure of Io's atmosphere , 1994 .

[47]  D. Tholen,et al.  Compositional Surface Diversity in the Trans-Neptunian Objects , 2000 .

[48]  J. Colmont,et al.  Pressure broadening of millimeter lines of carbon monoxide , 1987 .

[49]  Nicolas Thomas,et al.  Millimetric and optical observations of Chiron , 1997 .

[50]  Emmanuel Lellouch,et al.  The Spectrum of Comet Hale-Bopp (C/1995 O1) Observed with the Infrared Space Observatory at 2.9 Astronomical Units from the Sun , 1997, Science.

[51]  A. Winnberg,et al.  The Activity of Comet 29P/Schwassmann–Wachmann 1 Monitored through Its CO J=2→1 Radio Line☆ , 2001 .