Detection of CO and HCN in Pluto's atmosphere with ALMA
arXiv:1606.03293 · doi:10.1016/j.icarus.2016.10.013
Abstract
Observations of the Pluto-Charon system, acquired with the ALMA interferometer on June 12-13, 2015, have yielded a detection of the CO(3-2) and HCN(4-3) rotational transitions from Pluto, providing a strong confirmation of the presence of CO, and the first observation of HCN, in Pluto's atmosphere. The CO and HCN lines probe Pluto's atmosphere up to ~450 km and ~900 km altitude, respectively. The CO detection yields (i) a much improved determination of the CO mole fraction, as 515+/-40 ppm for a 12 ubar surface pressure (ii) clear evidence for a well-marked temperature decrease (i.e., mesosphere) above the 30-50 km stratopause and a best-determined temperature of 70+/-2 K at 300 km, in agreement with recent inferences from New Horizons / Alice solar occultation data. The HCN line shape implies a high abundance of this species in the upper atmosphere, with a mole fraction >1.5x10-5 above 450 km and a value of 4x10-5 near 800 km. The large HCN abundance and the cold upper atmosphere imply supersaturation of HCN to a degree (7-8 orders of magnitude) hitherto unseen in planetary atmospheres, probably due to the slow kinetics of condensation at the low pressure and temperature conditions of Pluto's upper atmosphere. HCN is also present in the bottom ~100 km of the atmosphere, with a 10-8 - 10-7 mole fraction; this implies either HCN saturation or undersaturation there, depending on the precise stratopause temperature. The HCN column is (1.6+/-0.4)x10^14 cm-2, suggesting a surface-referred net production rate of ~2x10^7 cm-2s-1. Although HCN rotational line cooling affects Pluto's atmosphere heat budget, the amounts determined in this study are insufficient to explain the well-marked mesosphere and upper atmosphere's ~70 K temperature. We finally report an upper limit on the HC3N column density (< 2x10^13 cm-2) and on the HC15N / HC14N ratio (< 1/125).
arXiv commentRevised version. Icarus, in press, Oct. 11, 2016. 57 pages, including 13 figures and 4 tables
References in corpus (14)
- The Pluto system: Initial results from its exploration by New Horizons
- Surface Compositions Across Pluto and Charon
- The Atmosphere of Pluto as Observed by New Horizons
- Pluto's lower atmosphere structure and methane abundance from high-resolution spectroscopy and stellar occultations
- Pluto's Seasons: New Predictions for New Horizons
- Ethyl cyanide on Titan: Spectroscopic detection and mapping using ALMA
- Pluto's atmosphere from the 29 June 2015 ground-based stellar occultation at the time of the New Horizons flyby
- Near-Infrared Spectral Monitoring of Pluto's Ices: Spatial Distribution and Secular Evolution
- High resolution spectroscopy of Pluto's atmosphere: detection of the 2.3 m CH bands and evidence for carbon monoxide
- Pluto's atmosphere from stellar occultations in 2012 and 2013
- Exploring the spatial, temporal, and vertical distribution of methane in Pluto's atmosphere
- Stratospheric aftermath of the 2010 Storm on Saturn as observed by the TEXES instrument. I. Temperature structure
- Discovery of carbon monoxide in the upper atmosphere of Pluto
- Evolution of an Early Titan Atmosphere: Comment
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