Synergistic Observations of Io’s atmosphere from the near-UV and the mid-IR Constantine Tsang, John Spencer, Kandis-Lea Jessup Department of Space Studies, Southwest Research Institute Boulder, Colorado Other Collaborators: Emmanuel Lellouch, Miguel Lopez Valverde Matthew Richter, Tommy Greathouse Io Workshop 2012, July 10 -11, LASP Boulder, Colorado
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Synergistic Observations of Io’s atmosphere from the near-UV and the mid-IR
Constantine Tsang, John Spencer, Kandis-Lea JessupDepartment of Space Studies, Southwest Research Institute
Boulder, Colorado
Other Collaborators: Emmanuel Lellouch, Miguel Lopez Valverde
Matthew Richter, Tommy Greathouse
Io Workshop 2012, July 10 -11, LASP Boulder, Colorado
Synergistic Observations of Io’s atmosphere from the near-UV and the mid-IR
Recap: The problem posed and progress
Part 1: Mechanisms of Atmospheric Support: Seasonal observations of atmosphere from mid-infrared (DPS-2011)
Part 2: Overall Atmospheric Density: HST-COS observations in the near-UV (LPSC-2012)
Io Workshop 2012, July 10 -11, LASP Boulder, Colorado
Synergistic Observations Of Io’s Atmosphere From Near-UV And Mid-IR, Constantine Tsang
Io’s Atmosphere: Characteristics
Primarily SO2, with traces of S, SO, O, NaClPressure= ~1 nbar, spatially variable
SO2 mapping from HST/STIS(Feaga et al. Icarus 2009){FUV Lyman-A}
Latitudinal profile from HST/STIS(Jessup et al. Icarus 2004) {0.2-0.3µm}
Longitudinal profile from IRTF/TEXES(Spencer et al. Icarus 2005){MIR 19 µm}
First scale height ~ 10km
Io’s Atmosphere: Support By Direct Volcanic Injection Or Frost Sublimation, Constantine Tsang
Io’s Atmosphere: Mechanism of Support?
Transport away horizontally, vertically
Volcanic Injection
Frost Sublimation?
?
Diagram by Andrew Walker
Io’s Atmosphere: Vapor Pressure Equilibrium
SO2
Num
ber
Den
sity
(cm
-2)
Synergistic Observations Of Io’s Atmosphere From Near-UV And Mid-IR, Constantine Tsang
PART 1: Io’s Atmosphere: Evidence for Support?
Sublimation support by SO2 surface frost:
Changes in neutral emissions during eclipse (Saur and Strobel 2004, Retherford et al. 2007)Latitudinal distribution of the atmosphere (Jessup et al. 2004)Correlation of densest atmospheric longitudes with frost distribution (Spencer et al. 2005)
Volcanic support by SO2 gas injection:
Dawn-to-dusk extent of atmosphere in Ly-α absorption (Strobel and Wolven 2001)Correlation of densest atmospheric longitudes with plume distribution (Feaga et al. 2009)
Separate out the sublimation component1) Observe Io during daily eclipses
2) Observe Io during seasons
Synergistic Observations Of Io’s Atmosphere From Near-UV And Mid-IR, Constantine Tsang
Seasonal Observations: The Theory
Requires yearly, regular observations of Io for 11 years...
Can we measure the effect of seasons on Io during the Jupiter year? (not to be confused with Earths season due to inclination)
- Does this translate to increased heating of the surface, more frost sublimation, greater global atmospheric density?
(Disc-integrated model incorporating surface temperature distribution)
Synergistic Observations Of Io’s Atmosphere From Near-UV And Mid-IR, Constantine Tsang
Seasonal Observations: Trends & Thermophysicals
Standard 1-dimensional numerical thermal model (Spencer et al. 1989, Howett et al. 2011) used to calculate frost surface temperature vs. time and heliocentric distance (diurnal and seasonal)
[Note: peak diurnal temperature is used to model the sub-solar SO2 abundance]
Synergistic Observations Of Io’s Atmosphere From Near-UV And Mid-IR, Constantine Tsang
Correlation of Bolometric albedo maps (Simonelli et al. 2001) and SO2 frost coverage (Doute et al. 2001) suggest SO2 rich-regions have albedos greater than 0.55, (ie: low TI more plausible)
(Small subset of satisfactory fits from 150 - 1250 MKS, 0.613-0.425 albedo)
Synergistic Observations Of Io’s Atmosphere From Near-UV And Mid-IR, Constantine Tsang
Seasonal Observations: Further 2012 Constraints
Synergistic Observations Of Io’s Atmosphere From Near-UV And Mid-IR, Constantine Tsang
Pre-2012 observations (pub.) With Jan 2012
2012 Observations post-perihelion already makes a significant different to constrain the amplitude of the density variations and thus the thermophysical properties
January 2012 observation takenOctober 2012 due to be taken
PART 2: Io’s Atmospheric Density
Synergistic Observations Of Io’s Atmosphere From Near-UV And Mid-IR, Constantine Tsang
Do observations of atmospheric density (+ distribution) as derived from different wavelengths agree (UV-IR-MM)?
Previous observations have not always given a consistent picture (some disc-resolved, others disc-averaged)
Spencer et al (2005)Longitudinal coverage
0.5 - 1.5 x 1017 cm-2 19 µm (mir) modified latitude model
Lellouch et al. (2003)Leading and Trailing
0.6 x 1017 cm-2 1.3 - 2 mm (mm) fractional coverage
Trafton et al. (1996)Leading and Trailing
0.05 - 0.07 x 1017 cm-2
< 0.96 x 1017 cm-22097 - 2136 A (uv)
uniform/fractional coverage
Disc-Averaged Atmospheric Densities
Io in near-UV: HST-COS 2010 Observations
Synergistic Observations Of Io’s Atmosphere From Near-UV And Mid-IR, Constantine Tsang
- HST Cosmic Origins Spectrometer disc-integrated observations of Io using G225M grating, with R~20,000- COS data re-binned and ratioed to SORCE-SOLSTICE observations of solar Fraunhofer lines
Near-UV Observations: HST-COS 2010
Synergistic Observations Of Io’s Atmosphere From Near-UV And Mid-IR, Constantine Tsang
HST-COS observations taken in 1st week of October 2010, spread evenly across Io longitude
Near-UV Observations: UV Atmosphere Model
Synergistic Observations Of Io’s Atmosphere From Near-UV And Mid-IR, Constantine Tsang
UV transmission model from kandis-lea jessup
- SO2 absorption bands sensitive to SO2, with small sensitivity to Tatm and SO column
density
- Not sensitive to surface temperature
Near-UV Observations: HST-COS 2010
Synergistic Observations Of Io’s Atmosphere From Near-UV And Mid-IR, Constantine Tsang
Disc-average model assuming a modified latitude model for both UV and IR
Minimization routine fits for SO2 band depth, albedo slope (linear), Tso2 and/or SO band depth
2100 A Band Strength
Synergistic Observations in 2010
Synergistic Observations Of Io’s Atmosphere From Near-UV And Mid-IR, Constantine Tsang
HST-COS near-UVOctober 2010
2100 - 2230 AR~20,000
IRTF-TEXES mid-IRJune 2010
529 - 531 cm-1 (18.9 µm)R~57,000
Near-UV Observations: HST-COS 2010
Synergistic Observations Of Io’s Atmosphere From Near-UV And Mid-IR, Constantine Tsang
Quasi-simultaneous observations of atmospheric density (0.5 - 1.7 x 1017 cm-2) in the near-UV and mid-IR are consistent with an atmosphere distributed according to the modified latitude model
HST-COS data shows little sensitivity to Tatm and SO density (upper limit = 3 x 1015 cm-2)
Conclusions
Synergistic Observations Of Io’s Atmosphere From Near-UV And Mid-IR, Constantine Tsang
Mid-IR seasonal observations
Synergistic UV and IR
19 µm observations from IRTF-TEXES show atmospheric density sensitive to seasonal variations in solar insolation
By fitting the amplitude and magnitude of these variations, we can measure the thermophysical properties of SO2 frost and separate out sublimation and volcanic contributions to the overall density
2100 A observations from HST-COS show near-UV retrieved atmospheric density is compatible with densities derived from the mid-IR
Future studies of atm. density need to take into account not only the longitudinal and latitudinal variations, but also heliocentric (seasonal variability) dependency.