Urey Prize Lecture. Io's Atmosphere: Not Yet Understood

Lellouch, E.

doi:10.1006/icar.1996.0186

Cited by 89 publications

(60 citation statements)

References 16 publications

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“…Disk-integrated mm-wave observations of SO 2 emission lines require local concentrations of a few × 10 17 cm -2 of SO 2 at temperatures > 600 K to match observed line widths, if the atmosphere is static (Lellouch et al 1992): such high temperatures are difficult to explain . Lower temperatures, and local abundances of about 1 × 10 17 cm -2 , more consistent with the UV results, are possible if mm line widths are due to rapid motions associated with plumes or supersonic winds ( (Ballester et al 1994, Lellouch 1996. In addition to SO 2 , lesser amounts of SO , NaCl (Lellouch et al 2003) and S 2 (Spencer et al 2000a) have also been detected, as have neutral atomic emissions from S, O, and Na (Ballester et al 1987, Geissler et al 1999a, 2001a, Feaga et al 2002, Roesler et al 1999, Bouchez et al 2000, and molecular emissions from SO (dePater et al 2002) and, probably, SO 2 and/or S 2 (Geissler et al 1999a, 2001a, Jessup et al 2004).…”

Section: Introductionsupporting

confidence: 51%

“…Comparing our results with those obtained from the millimeter data (Lellouch et al 1992, Lellouch 1996) is not straightforward given the different data characteristics. First, the mm data primarily sample the leading and trailing sides, and do not easily provide information on the Jupiter-facing and anti-Jupiter hemispheres because of contamination by Jupiter radiation.…”

Section: Comparison With Millimeter and Lyman-α Datamentioning

confidence: 42%

“…13), the SO 2 lines are always seen in absorption. This is in contrast to the mm-wave region where SO 2 lines are always seen in emission (Lellouch et al 1992, Lellouch 1996, and as our modeling shows (Figs,3,9,10,11) emission lines are also possible in the mid-IR for some atmospheric conditions. The fact that emission lines are not observed on Io therefore immediately rules out models (other than the end-member volcanicatmosphere-only models shown in Fig.…”

Section: Overall Spectrum Shapementioning

confidence: 50%

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Mid-infrared detection of large longitudinal asymmetries in Io's SO atmosphere

Spencer¹,

Lellouch²,

Richter³

et al. 2005

Icarus

103

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We have observed about 16 absorption lines of the ν 2 SO 2 vibrational band on Io, in disk-integrated 19 µm spectra taken with the TEXES high spectral resolution mid-infrared spectrograph at the NASA Infrared Telescope Facility in November 2001, December 2002, and January 2004 These are the first ground-based infrared observations of Io's sunlit atmosphere, and provide a new window on the atmosphere that allows better longitudinal and temporal monitoring than previous techniques. Dramatic variations in band strength with longitude are seen that are stable over at least a 2 year period. The depth of the strongest feature, a blend of lines centered at 530.42 cm -1 , varies from about 7% near longitude 180 to about 1% near longitude 315 W, as measured at a spectral resolution of 57,000. Interpretation of the spectra requires modeling of surface temperatures and atmospheric density across Io's disk, and the variation in non-LTE ν 2 vibrational temperature with altitude, and depends on the assumed atmospheric and surface temperature structure. About half of Io's 19µm radiation comes from the sun-heated surface, and half from volcanic hot spots with temperatures primarily between 150 and 200 K, which occupy about 8% of the surface. The observations are thus weighted towards the atmosphere over these lowtemperature hot spots. If we assume that the atmosphere over the hot spots is representative of the atmosphere elsewhere, and that the atmospheric density is a function of latitude, the most plausible interpretation of the data is that the equatorial atmospheric column density varies from about 1.5 x 10 17 cm -2 near longitude 180 W to about 1.5 x 10 16 cm -2 near longitude 300 W, roughly consistent with HST UV spectroscopy and Lyman-α imaging. The inferred atmospheric kinetic temperature is less than about 150 K, at least on the anti-Jupiter hemisphere where the bands are strongest, somewhat colder than inferred from HST UV spectroscopy and millimeter-wavelength spectroscopy. This longitudinal variability in atmospheric density correlates with the longitudinal variability in the abundance of optically thick, near-UV bright SO 2 frost. However it is not clear whether the correlation results from volcanic control (regions of large frost abundance result from greater condensation of atmospheric gases supported by more vigorous volcanic activity in these regions) or sublimation control (regions of large frost abundance produce a more extensive atmosphere due to more extensive sublimation). Comparison of data taken in 2001, 2002, and 2004 shows that with the possible exception of longitudes near 180 W between 2001 and 2002, Io's atmospheric density does not appear to decrease as Io recedes from the sun, as would be expected if the atmosphere were supported by the sublimation of surface frost, suggesting that the atmosphere is dominantly supported by direct volcanic supply rather than by frost sublimation. However, other evidence such as the smooth variation in atmospheric abundance with latitude, and atmospheric ch...

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Section: Introductionsupporting

confidence: 51%

Section: Comparison With Millimeter and Lyman-α Datamentioning

confidence: 42%

Section: Overall Spectrum Shapementioning

confidence: 50%

See 1 more Smart Citation

Mid-infrared detection of large longitudinal asymmetries in Io's SO atmosphere

Spencer¹,

Lellouch²,

Richter³

et al. 2005

Icarus

103

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“…These observations and the detection of SO2 dissociation products in Io's atmosphere imply that SO2 is a major constituent in the lower atmosphere, where the primary sources of SO2 are expected to be volcanic activity and sublimation of surface frost. To date, there are significant uncertainties concerning the atmospheric abundance and spatial distribution of SO2 on Io, the thermal structure of the atmosphere, and the role of thermal processes involving surface frosts in the formation of the atmosphere Summers and Strobel, 1996;Lellouch, 1996]. Ballester et al [1994] first reported that the albedo of Io below about 220 nm is dominated by SO2 absorption band Belton [1982], saturation of the very sharp SO2 features may lead to large underestimates of the SO2 column density when instrumentally broadened absorption spectra are analyzed with low-resolution laboratoryderived cross sections.…”

Section: So2 In Planetary Atmospheresmentioning

confidence: 99%

High‐resolution photoabsorption cross‐section measurements of SO₂ at 295 K between 198 and 220 nm

Stark¹,

Smith²,

Rufus³

et al. 1999

J. Geophys. Res.

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Abstract. SO2 is an important constituent of the atmospheres of Io and Venus. Accurate photoabsorption cross-section data at the temperatures of these planetary atmospheres are required for the interpretation of SO2 observations and for reliable photochemical models. As part of a planned series of measurements over the 160-300 K range, photoabsorption cross sections of SO2 at 295 K, in the wavelength region 198-220 nm, have been determined from very high resolution (resolving power (X/AX) • 450,000) absorption spectra recorded with a vacuum ultraviolet Fourier transform spectrometer. These new measurements are compared with earlier, lower-resolution (X/AX • 100,000) photoabsorption measurements at 213 K spanning the same wavelength region, with lower-resolution (X/AX = 100,000) measurements at 295 K in a more limited region, and with a recent Doppler-limited laser diode measurement at 295 K over a very narrow wavelength region.

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“…Moreno et al [13] used continuum computational fluid dynamics modeling of the volcanic plumes to characterize the nature of both the near-vent behavior as well as the spread of the down-falling gas over the planet. Lellouch [14] reported that Kieffer experienced numerical difficulties when modeling the underexpanded plumes on Io.…”

Section: Introductionmentioning

confidence: 99%

DSMC Modeling of Gasdynamics, Radiation and Fine Particulates in Ionian Volcanic Jets

Zhang¹,

Goldstein²,

Varghese³

et al. 2003

AIP Conference Proceedings

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Urey Prize Lecture. Io's Atmosphere: Not Yet Understood

Cited by 89 publications

References 16 publications

Mid-infrared detection of large longitudinal asymmetries in Io's SO atmosphere

Mid-infrared detection of large longitudinal asymmetries in Io's SO atmosphere

High‐resolution photoabsorption cross‐section measurements of SO₂ at 295 K between 198 and 220 nm

DSMC Modeling of Gasdynamics, Radiation and Fine Particulates in Ionian Volcanic Jets

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Urey Prize Lecture. Io's Atmosphere: Not Yet Understood

Cited by 89 publications

References 16 publications

Mid-infrared detection of large longitudinal asymmetries in Io's SO atmosphere

Mid-infrared detection of large longitudinal asymmetries in Io's SO atmosphere

High‐resolution photoabsorption cross‐section measurements of SO2 at 295 K between 198 and 220 nm

DSMC Modeling of Gasdynamics, Radiation and Fine Particulates in Ionian Volcanic Jets

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Product

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High‐resolution photoabsorption cross‐section measurements of SO₂ at 295 K between 198 and 220 nm