The abundance profile of CO in Neptune's atmosphere

Hesman, B. E.; Davis, G. R.; Matthews, H. E.; Orton, Glenn S.

doi:10.1016/j.icarus.2006.08.025

Cited by 50 publications

(115 citation statements)

References 24 publications

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“…Vigorous vertical advection of both gaseous CH 4 and CH 4 ice (which subsequently sublimates) was invoked to explain the stratospheric abundance. Such rapid convection is consistent with observations of Neptune's strong internal heat flux, the disequilibrium of para-hydrogen (Conrath et al 1998), the high levels of tropospheric CO determined from the sub-mm (Hesman et al 2007) and with the visible observations of thick, high clouds casting shadows on deeper levels in Voyager 2 images. However, convective cloud activity is typically restricted to Neptune's mid-latitudes and is time-variable (e.g.…”

Section: Introductionsupporting

confidence: 87%

“…Although the existence of CO in Neptune's stratosphere has been known since the first millimeter wavelength observations of Marten et al (1993), AKARI is the first instrument to observe the fluorescent emission of CO at 4.7 μm. Furthermore, the non-LTE modeling confirms the findings of Hesman et al (2007) that an additional reservoir of CO is needed in the upper troposphere to fit the spectra. Thus Neptune's CO abundance is a combination of CO from the thermochemistry of carbon and oxygen in the deep atmosphere, advected to altitudes accessible to remote sensing, in addition to stratospheric CO from external sources.…”

Section: Atmospheric Compositionsupporting

confidence: 82%

“…Thus Neptune's CO abundance is a combination of CO from the thermochemistry of carbon and oxygen in the deep atmosphere, advected to altitudes accessible to remote sensing, in addition to stratospheric CO from external sources. Our CO distribution (CO/H 2 = 2.5 × 10 −6 in the stratosphere, decreasing by a factor of four below 10 mbar) is entirely consistent with the best-fitting result of Hesman et al (2007). The fluorescent emission spectra are inconsistent with the constant vertical CO distribution proposed by Marten et al (1993) to fit the first measurements of CO emission in the millimeter range.…”

Section: Atmospheric Compositionsupporting

confidence: 77%

“…9: -Profile 1: CO limited to the stratosphere alone with a variable mixing ratio (constant with altitude). mixing ratio of CO/H 2 = 2.5 × 10 −6 , decreasing to zero below 10 mbar; -Profile 2: similar to the CO profile retrieved from the submillimeter range (Hesman et al 2007), CO is present in both the stratosphere and troposphere.…”

Section: Co Emissionmentioning

confidence: 61%

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Neptune's atmospheric composition from AKARI infrared spectroscopy

Fletcher

Drossart

Burgdorf

et al. 2010

A&A

115

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Aims. Disk-averaged infrared spectra of Neptune between 1.8 and 13 μm, obtained by the AKARI infrared camera (IRC) in May 2007, have been analysed to (a) determine the globally-averaged stratospheric temperature structure; (b) derive the abundances of stratospheric hydrocarbons; and (c) detect fluorescent emission from CO at 4.7 μm. Methods. Mid-infrared spectra (SG1 and SG2 channels of AKARI/IRC), with spectral resolutions of 47 and 34 respectively, were modelled using a line-by-line radiative transfer code to determine the temperature structure between 1-1000 μbar and the abundances of CH 4 , CH 3 D and higher-order hydrocarbons. A full non-LTE radiative model was then used to determine the best fitting CO profile to reproduce the fluorescent emission observed at 4.7 μm in the NG channel (with a spectral resolution of 135). Results. The globally-averaged stratospheric temperature structure is quasi-isothermal between 1-1000 μbar, which suggests little variation in global stratospheric conditions since studies by the Infrared Space Observatory a decade earlier. The derived CH 4 mole fraction of (9.0 ± 3.0) × 10 −4 at 50 mbar, decreasing to (0.9 ± 0.3) × 10 −4 at 1 μbar, is larger than that expected if the tropopause at 56 K acts as an efficient cold trap, but consistent with the hypothesis that CH 4 leaking through the warm south polar tropopause (62-66 K) is globally redistributed by stratospheric motion. The ratio of D/H in CH 4 of 3.0 ± 1.0 × 10 −4 supports the conclusion that Neptune is enriched in deuterium relative to the other giant planets. We determine a mole fraction of ethane of (8.5 ± 2.1) × 10 −7 at 0.3 mbar, consistent with previous studies, and a mole fraction of ethylene of 5.0 +1.8 −2.1 × 10 −7 at 2.8 μbar. An emission peak at 4.7 μm is interpreted as a fluorescent emission of CO, and requires a vertical distribution with both external and internal sources of CO. Finally, comparisons to previous L-band studies indicate significant variability of Neptune's flux densities in the 3.5-4.1 μm range, related to changes in solar energy deposition.

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Section: Introductionsupporting

confidence: 87%

Section: Atmospheric Compositionsupporting

confidence: 82%

Section: Atmospheric Compositionsupporting

confidence: 77%

Section: Co Emissionmentioning

confidence: 61%

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Neptune's atmospheric composition from AKARI infrared spectroscopy

Fletcher

Drossart

Burgdorf

et al. 2010

A&A

115

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“…In the past decade, observations of CO in the millimeter and submillimeter ranges at Saturn and Neptune have tentatively shown that the external source for this species may be ancient comet impacts (Lellouch et al , 2010aHesman et al 2007; and Luszcz-Cook and de Pater 2013, for Neptune, and Cavalié et al 2010 for Saturn). At Uranus, a cometary origin for CO is possible (Cavalié et al 2014).…”

Section: Beyond Jupitermentioning

confidence: 99%

Constraints from Comets on the Formation and Volatile Acquisition of the Planets and Satellites

et al. 2015

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Comets play a dual role in understanding the formation and evolution of the solar system. First, the composition of comets provides information about the origin of the giant planets and their moons because comets formed early and their composition is not expected to have evolved significantly since formation. They, therefore serve as a record of conditions during the early stages of solar system formation. Once comets had formed, their orbits were perturbed allowing them to travel into the inner solar system and impact the planets. In this way they contributed to the volatile inventory of planetary atmospheres. We review here how knowledge of comet composition up to the time of the Rosetta mission has contributed to understanding the formation processes of the giant planets, their moons and small icy bodies in the solar system. We also discuss how comets contributed to the volatile inventories of the giant and terrestrial planets.

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