Synergistic Observations of Io’s atmosphere from the near ...con/ioworkshop2012/Program_files/Tsa… · Io Workshop 2012, July 10 -11, LASP Boulder, Colorado. Synergistic Observations

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)


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


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?

SunJupiter

AphelionPerihelionJupiter

(Not to scale)

Orbit period=11 years(jupiter e=0.048, earth e=0.016)

4.95 AU 5.46 AU

Fsolar = 45.9 Wm-2Fsolar = 55.9 Wm-2

Increase of ~20%


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 µmSO2 υ2 vibrational band at 18.9 µm (~530 cm-1)

Data for 2001, 2002, 2004, 2005, 2007, 2009, 2010, 2012

Seasonal Observations: Mid-infrared 19µm SO2

Tsang et al. 2012, Icarus, 217, 277-296


- Emission and absorption spectra depends on i) surface temperature, ii) atmospheric kinetic temperature, iii) SO2 column density.

- Spectrum shape is atm. temperature dependent, allowing some independent constraints

Seasonal Observations: Spectral fits and Sensitivities

Low T, low SO2High T, high SO2


Seasonal Observations: Yearly Observations

Blue: SO2 sub-solar column density (Co-retrieved) 0.55 ± 0.4 (2005) - 1.37 ± 0.1 [x1017 cm-2] (2010)

Red: Kinetic temperature (Co-retrieved) 92 - 127 K (mean= 108 ± 18 K)

Purple: SO2 sub-solar column density (Tgas=110K) 0.61 ± 0.15 (2005) - 1.51 ± 0.2 [x1017 cm-2] (2010)

(Disc-integrated model incorporating surface temperature distribution)


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]


Tsang et al. 2012, Icarus, 217, 277-296

Thermal Inertia (MKS) Bond Albedo

Volcanic Component (x1016 cm-2)

Sublimation Support

(Perihelion)

Sublimation Support

(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 53.41250 0.425 1.0 94.1% 83.9%

Seasonal Observations: Thermal Inertia & Albedos

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)


Seasonal Observations: Further 2012 Constraints


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


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


- 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


HST-COS observations taken in 1st week of October 2010, spread evenly across Io longitude

Near-UV Observations: UV Atmosphere Model


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



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


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



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


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.

Documents

Synergistic Observations of Io’s atmosphere from the near ...con/ioworkshop2012/Program_files/Tsa… · Io Workshop 2012, July 10 -11, LASP Boulder, Colorado. Synergistic Observations