The collapse of Io's primary atmosphere in Jupiter eclipse

Tsang, C. C. C.; Spencer, J. R.; Lellouch, E.; López‐Valverde, M. A.; Richter, Matthew J.

doi:10.1002/2016je005025

Cited by 31 publications

(38 citation statements)

References 31 publications

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“…Tsang et al () did not detect post eclipse change in absorption by SO 2 at near‐ultraviolet (NUV) wavelengths. Yet infrared (IR) observations of Io going into eclipse by Tsang et al () revealed changes in the SO 2 absorption, consistent with a drop of the SO 2 column density by a factor of 5.…”

Section: Introductionmentioning

confidence: 76%

“…Io's SO 2 dominated atmosphere is tenuous and highly spatially variable. Previous ground‐based observation of the Io's atmosphere showed that its surface temperature drops and atmospheric column density collapses within ∼20 min past eclipse (see Figure of Tsang et al, ).…”

Section: Resultsmentioning

confidence: 96%

“…The blue vertical lines indicate the typical timescales over which a change in the electrodynamic interaction would propagate after ingress and egress, based on the Alfvén travel times. The orange vertical lines indicate the typical timescale of 20 min of the collapse of Io's atmosphere (see Figure 3 of Tsang et al, 2016) The Alfvén travel time was calculated using a 3-D plasma torus model, combined with the JRM09 magnetic field model (Hinton et al, 2019). This information provides a typical timescale over which one would expect The PJ3 data set provided the best coverage of the footprint during eclipse, as of PJ15 (7 September 2018).…”

Section: Contribution From the Eclipse On The Footprint Emitted Powermentioning

confidence: 99%

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Juno‐UVS Observation of the Io Footprint During Solar Eclipse

et al. 2019

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The two main ultraviolet‐signatures resulting from the Io‐magnetosphere interaction are the local auroras on Io's atmosphere, and the Io footprints on Jupiter. We study here how Io's daily eclipses affect the footprint. Previous observations showed that its atmosphere collapses in eclipse. While remote observers can observe Io's local auroras briefly when Io disappears behind Jupiter, Juno is able to follow the Io footprint in the unlit hemisphere. Theoretical models of the variability of the energy flux fed into the Alfvén wings, ultimately powering the footprints, are not sufficiently constrained by observations. For the first time, we use observations of Io's footprint from the Ultraviolet Spectrograph (UVS) on Juno recorded as Io went into eclipse. We benchmark the trend of the footprint brightness using observations by UVS taken over Io's complete orbit and find that the footprint emitted power variation with Jupiter's rotation shows fairly consistent trends with previous observations. Two exploitable data sets provided measurements when Io was simultaneously in eclipse. No statistically significant changes were recorded as Io left and moved into eclipse, respectively, suggesting either that (i) Io's atmospheric densities within and outside eclipse are large enough to produce a saturated plasma interaction, that is, in the saturated state, changes in Io's atmospheric properties to first order do not control the total Alfvénic energy flux, (ii) the atmospheric collapse during the Juno observations was less than previously observed, or (iii) additional processes of the Alfvén wings in addition to the Poynting flux generated at Io control the footprint luminosity.

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Section: Introductionmentioning

confidence: 76%

Section: Resultsmentioning

confidence: 96%

Section: Contribution From the Eclipse On The Footprint Emitted Powermentioning

confidence: 99%

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Juno‐UVS Observation of the Io Footprint During Solar Eclipse

et al. 2019

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“…Under this scenario, the required bulk atmospheric gas density and surface pressure are n ∼ 10 11 cm −3 and 1-3 nbar, consistent with observations and modeling of Io's dayside atmosphere at altitudes below 10 km (Lellouch et al 2007; Walker et al 2010). These densities and pressures would be too high for the nightside density if the atmospheric density drops by an order of magnitude or more at night (as predicted by sublimation-supported models), but recent results have shown a drop in SO 2 gas density of only a factor of 5±2 (Tsang et al 2016). While our observations taken immediately post-ingress and pre-egress (on different dates) prefer models with only a factor of 1.5 change in gas density, a factor of 5 change is still well within uncertainties.…”

mentioning

confidence: 99%

“…While our observations taken immediately post-ingress and pre-egress (on different dates) prefer models with only a factor of 1.5 change in gas density, a factor of 5 change is still well within uncertainties. In addition, our derived gas densities are for the total bulk atmosphere, while Tsang et al (2016) specifically measured SO 2 . The low-temperature gas component is warmer for observations in the first 20 minutes of eclipse (in Dec 2015) than after Io had been in shadow for 1.5 hours (in May 2016), suggesting cooling of the atmosphere during eclipse.…”

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confidence: 99%

Emission from volcanic SO gas on Io at high spectral resolution

Kleer

Pater

Ádámkovics

2019

Icarus

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Jupiter's moon Io hosts a dynamic atmosphere that is continually stripped off and replenished through frost sublimation and volcanic outgassing. We observed an emission band at 1.707 µm thought to be produced by hot SO molecules directly ejected from a volcanic vent; the observations were made the NIRSPEC instrument on the Keck II telescope while Io was in eclipse by Jupiter on three nights in 2012-2016, and included two observations with 10× higher spectral resolution than all prior observations of this band. These high-resolution spectra permit more complex and realistic modeling, and reveal a contribution to the SO emission from gas reservoirs at both high and low rotational temperatures. The scenario preferred by de Pater et al. (2002) for the source of the SO gas -direct volcanic emission of SO in the excited state -is consistent with these two temperature components if the local gas density is high enough that rotational energy can be lost collisionally before the excited electronic state spontaneously decays. Under this scenario, the required bulk atmospheric gas density and surface pressure are n ∼ 10 11 cm −3 and 1-3 nbar, consistent with observations and modeling of Io's dayside atmosphere at altitudes below 10 km (Lellouch et al. 2007; Walker et al. 2010). These densities and pressures would be too high for the nightside density if the atmospheric density drops by an order of magnitude or more at night (as predicted by sublimation-supported models), but recent results have shown a drop in SO 2 gas density of only a factor of 5±2 (Tsang et al. 2016). While our observations taken immediately post-ingress and pre-egress (on different dates) prefer models with only a factor of 1.5 change in gas density, a factor of 5 change is still well within uncertainties. In addition, our derived gas densities are for the total bulk atmosphere, while Tsang et al. (2016) specifically measured SO 2 . The low-temperature gas component is warmer for observations in the first 20 minutes of eclipse (in Dec 2015) than after Io had been in shadow for 1.5 hours (in May 2016), suggesting cooling of the atmosphere during eclipse. However, individual spectra during the first ∼30 minutes of eclipse do not show a systematic cooling, indicating that such a cooling would have to take place on a longer timescale than the ∼10 minutes for cooling of the surface (Tsang et al. 2016). Excess emission is consistently observed at 1.69 µm, which cannot be matched by two-temperature gas models but can be matched by models that over-populate high rotational states. However, a detailed assessment of disequilibrium conditions will require high-resolution spectra that cover both the center of the band and the wing at 1.69 µm. Finally, a comparison of the total band strengths observed across eight dates from 1999-2016 reveals no significant dependence on thermal hot spot activity (including Loki Patera), on the time since Io has been in shadow, nor on the phase of Io's orbit at the time of observation.

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