Synergistic Observations of Ios atmosphere from the near-UV and the - PowerPoint PPT Presentation

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

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

Io’s Atmosphere: Characteristics Primarily SO 2 , with traces of S, SO, O, NaCl First scale height ~ 10km Pressure= ~1 nbar, spatially variable Latitudinal profile from HST/STIS Longitudinal profile from (Jessup et al. Icarus 2004) IRTF/TEXES {0.2-0.3 µ m} (Spencer et al. Icarus 2005) {MIR 19 µ m} SO 2 mapping from HST/ STIS (Feaga et al. Icarus 2009) {FUV Lyman-A} Synergistic Observations Of Io’s Atmosphere From Near-UV And Mid-IR, Constantine Tsang

Io’s Atmosphere: Transport away horizontally, Mechanism of Support? vertically ? Frost Sublimation Volcanic Injection ? Diagram by Andrew Walker Io’s Atmosphere: Support By Direct Volcanic Injection Or Frost Sublimation, Constantine Tsang

Io’s Atmosphere: Vapor Pressure Equilibrium SO 2 Number Density (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 SO 2 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 SO 2 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 component 1) 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 Can we measure the effect of seasons on Io during the Jupiter year? (not to be confused with Earths season due to inclination) (Not to scale) 4.95 AU 5.46 AU Jupiter Jupiter F solar = 55.9 Wm -2 F solar = 45.9 Wm -2 Increase of ~20% Aphelion Sun Perihelion Orbit period=11 years (jupiter e=0.048, earth e=0.016) - Does this translate to increased heating of the surface, more frost sublimation, greater global atmospheric density? Requires yearly, regular observations of Io for 11 years... Synergistic Observations Of Io’s Atmosphere From Near-UV And Mid-IR, Constantine Tsang

Seasonal Observations: Mid-infrared 19µm SO 2 NASA’s Infrared Telescope Facility (IRTF) 3 m on Mauna Kea, TEXES: High resolution mid-IR spectrograph R = 50,000 - 75,000, λ = 5 - 25 µm SO 2 υ 2 vibrational band at 18.9 µm (~530 cm -1 ) Data for 2001, 2002, 2004, 2005, 2007, 2009, 2010, 2012 Tsang et al. 2012, Icarus , 217, 277-296 Synergistic Observations Of Io’s Atmosphere From Near-UV And Mid-IR, Constantine Tsang

Seasonal Observations: Spectral fits and Sensitivities High T, high SO 2 Low T, low SO 2 - Emission and absorption spectra depends on i) surface temperature, ii) atmospheric kinetic temperature, iii) SO 2 column density. - Spectrum shape is atm. temperature dependent, allowing some independent constraints Synergistic Observations Of Io’s Atmosphere From Near-UV And Mid-IR, Constantine Tsang

Seasonal Observations: Yearly Observations (Disc-integrated model incorporating surface temperature distribution) Blue : SO 2 sub-solar column density (Co-retrieved) 0.55 ± 0.4 (2005) - 1.37 ± 0.1 [x10 17 cm -2 ] (2010) Red : Kinetic temperature (Co-retrieved) 92 - 127 K (mean= 108 ± 18 K ) Purple : SO 2 sub-solar column density (T gas =110K) 0.61 ± 0.15 (2005) - 1.51 ± 0.2 [x10 17 cm -2 ] (2010) 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 SO 2 abundance] Tsang et al. 2012, Icarus , 217, 277-296 Synergistic Observations Of Io’s Atmosphere From Near-UV And Mid-IR, Constantine Tsang

Seasonal Observations: Thermal Inertia & Albedos Volcanic Sublimation Sublimation Thermal Bond Albedo Component Support Support Inertia (MKS) (x10 16 cm -2 ) (Perihelion) (Aphelion) 150 0.613 6.0 62.1% 18.8% 400 0.512 4.0 76.8% 39.2% 800 0.462 3.0 81.2 53.4 1250 0.425 1.0 94.1% 83.9% (Small subset of satisfactory fits from 150 - 1250 MKS, 0.613-0.425 albedo) Correlation of Bolometric albedo maps (Simonelli et al. 2001) and SO 2 frost coverage (Doute et al. 2001) suggest SO 2 rich-regions have albedos greater than 0.55, (ie: low TI more plausible) Synergistic Observations Of Io’s Atmosphere From Near-UV And Mid-IR, Constantine Tsang

Seasonal Observations: Further 2012 Constraints Pre-2012 observations (pub.) With Jan 2012 January 2012 observation taken October 2012 due to be taken 2012 Observations post-perihelion already makes a significant different to constrain the amplitude of the density variations and thus the thermophysical properties Synergistic Observations Of Io’s Atmosphere From Near-UV And Mid-IR, Constantine Tsang

PART 2: Io’s Atmospheric Density 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) Disc-Averaged Atmospheric Densities Spencer et al (2005) 19 µm (mir) 0.5 - 1.5 x 10 17 cm -2 modified latitude model Longitudinal coverage Lellouch et al. (2003) 1.3 - 2 mm (mm) 0.6 x 10 17 cm -2 fractional coverage Leading and Trailing 0.05 - 0.07 x 10 17 cm -2 Trafton et al. (1996) 2097 - 2136 A (uv) < 0.96 x 10 17 cm -2 Leading and Trailing uniform/fractional coverage Synergistic Observations Of Io’s Atmosphere From Near-UV And Mid-IR, Constantine Tsang

Io in near-UV: HST-COS 2010 Observations - 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 Synergistic Observations Of Io’s Atmosphere From Near-UV And Mid-IR, Constantine Tsang

Near-UV Observations: HST-COS 2010 HST-COS observations taken in 1st week of October 2010, spread evenly across Io longitude Synergistic Observations Of Io’s Atmosphere From Near-UV And Mid-IR, Constantine Tsang

Near-UV Observations: UV Atmosphere Model UV transmission model from kandis-lea jessup - SO 2 absorption bands sensitive to SO 2 , with small sensitivity to T atm and SO column density - Not sensitive to surface temperature Synergistic Observations Of Io’s Atmosphere From Near-UV And Mid-IR, Constantine Tsang

Near-UV Observations: HST-COS 2010 Disc-average model assuming a modified latitude model for both UV and IR 2100 A Band Strength Minimization routine fits for SO 2 band depth, albedo slope (linear), T so2 and/or SO band depth Synergistic Observations Of Io’s Atmosphere From Near-UV And Mid-IR, Constantine Tsang

Synergistic Observations in 2010 HST-COS near-UV October 2010 2100 - 2230 A R~20,000 IRTF-TEXES mid-IR June 2010 529 - 531 cm -1 (18.9 µm) R~57,000 Synergistic Observations Of Io’s Atmosphere From Near-UV And Mid-IR, Constantine Tsang

Near-UV Observations: HST-COS 2010 Quasi-simultaneous observations of atmospheric density (0.5 - 1.7 x 10 17 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 T atm and SO density (upper limit = 3 x 10 15 cm -2 ) Synergistic Observations Of Io’s Atmosphere From Near-UV And Mid-IR, Constantine Tsang

Conclusions Mid-IR seasonal observations 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 Synergistic UV and IR 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. Synergistic Observations Of Io’s Atmosphere From Near-UV And Mid-IR, Constantine Tsang