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

Abstract

Abstract.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. The observations were performed with the 30 m telescope of the Institut de Radioastronomie Millimétrique 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/N2 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× 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 (1999, 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 × 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.

On the Mass and Origin of Chariklo’s Rings

“…For these objects our simple model predicts CO loss rates between , depending on their current orbits, consistent with observations. But our explanation is not unique (e.g., Prialnik & Bar-Nun 1987), and a number of surveys (Rauer et al 1997;Bockelée-Morvan et al 2001;Jewitt et al 2008) have failed to detect CO around other Centaurs and KBOs. Some of these upper limits contradict our predictions (Figure 3): for the few largest Centaurs like Chariklo, Chiron, Pholus and Asbolus, we predict outgassing rates some one to two orders of magnitude above the observed upper limits.…”

“…This motivates us to focus on CO. We argue in Section 4.1.1 that while exposed CO on KBO surfaces would have sublimated long ago, CO should retain its primordial abundance in layers deeper than ∼1 km and could diffuse upward rapidly upon displacement of the KBOs to warmer regions of the solar system. This may explain the detection of CO outgassing in Comet 29P/SW1 (a = 6 au,R 15 km, Senay & Jewitt 1994;Crovisier et al 1995;Gunnarsson et al 2002), Comet Hale-Bopp (at a 7 au,R 20 km, Biver et al 1997), and possibly Centaur 2060 Chiron ( = a 13.7 au,R 100 km, Womack & Stern 1997, though this has been challenged by Rauer et al 1997;Bockelée-Morvan et al 2001). For these objects our simple model predicts CO loss rates between , depending on their current orbits, consistent with observations.…”

TNOs are Cool: A survey of the trans-Neptunian region

“…An upper limit of 5 × 10 27 s −1 for the CO production rate was measured in 1998/1999, when Chiron was at its minimum brightness (Bockelée-Morvan et al 2001), whereas a marginal detection (Womack & Stern 1999) and upper limits (Rauer et al 1997), all in the range (1-3) × 10 28 s −1 , were obtained from observations in 1995, just before its perihelion passage on February 1996.…”

The distant activity of the Long Period Comets C/2003 O1 (LINEAR) and C/2004 K1 (Catalina)

“…For the active Centaur 29P/Schwassmann-Wachmann, a Q CO ∼ 3.5 × 10 28 mol s −1 was measured around r h = 6 AU (Senay & Jewitt 1994;Crovisier et al 1995;Festou et al 2001). Womack & Stern (1999) derived a production rate of Q CO = 1.5 ± 0.8 × 10 28 mol s −1 for the active Centaur (2060) Chiron, although this marginal detetion has not been confirmed by independent observations (Rauer et al 1997;Bockelée-Morvan et al 2001). Only upper limits to the production rate have been derived for the LPC C/1999 J2 (Skiff) observed at r h = 7.2 AU (≤2 × 10 28 mol s Although the Q CO observed in distant cometary objects depends strongly on observational bias and heliocentric distance, we can summarise that a value in the range 1.5-3.5×10 28 mol s −1 could be considered to be typical for a heliocentric distance ∼6-8 AU.…”