IGRINS Science Workshop 2010 1 High Spectral Resolution Mid- Infrared Spectroscopy as a Probe of the...

1 IGRINS Science Workshop 2010

High Spectral Resolution Mid-Infrared Spectroscopy as a

Probe of the Physical State of Planetary Atmospheres

August 26, 2010


Advantages of High Spectral Resolution

• Increased sensitivity to unresolved spectral features (changes linearly with resolving power)

• Increases spectral separation of observed emission or absorption features allowing for unique identifications of a multitude of molecular features when molecular rotation-vibration bands overlap.

• Increases the amount of open spectral space to observation by reducing blending and increasing separation of telluric absorption features.

• The line shape of resolved spectral features can be use to retrieve information on velocity of the gas (compact H2 regions, galaxies, etc), information on vertical variation of temperature or abundance of molecules in a planetary atmosphere, or the ability to separate distinct clouds of gas along a given line of sight.


TEXES: Texas Echelon Cross Echelle Spectrograph

• Operates between 5 and 25 m• A ground based prototype for

EXES, an instrument to be flown on SOFIA


36 inches long0.3 inch groove spacing0.03 inch groove height

0.3”

0.3”

Echelon Grating


T.K. GreathouseJ.I. MosesJ.H. Lacy

M.J. Richter

NASA/JPL/Space Science Institute

Probing Stratospheric Chemistry, Energetics, and Dynamics.

A Detailed Study of Giant Planet Stratospheres


Pre

ssur

e (b

ar)

Temperature (Kelvin)

Troposphere

Stratosphere

Thermosphere

Tropopause

Mesosphere

Mesopause

Stratopause

General Atmospheric Structure


Process Dependencies

Stratospheric Temperatures

ChemistryLatitude?Season?

InsolationLatitudeSeasonSolar Flux

Molecular AbundancesLatitude?Season?Dynamic Mixing?

HeatingAerosols

ChemistryInsolationAdvection?

CoolingMolecular Abundances

ChemistryAdvection?

8 IGRINS Science Workshop 2010 Moses et al. 2000, Icarus.

Question:What molecules exist in the stratosphere?


Using Doppler Shifts for Unambiguous Detection of C3H8

First Detection of Propane on

Saturn

-2010 Latitude

-8010 Latitude


ISOSchulz et al. 1999

First Detections of C2H4 in Neptune


A Second Detection

AKARI data

Fletcher et al. 2010


The First Spectrally Resolved Detection of C2H4 on Neptune


Spectral Line SeparationThe Unambiguous Detection of

C3H8

Propane on Titan

Roe et al. 2003

Propane

• Measure weak lines• Measure features in crowded

spectral regions


Seasonal Studies


Temperature Retrievals

• Using thermal emission spectra to retrieve temperatures requires knowledge of mixing ratio of observed molecule.

• Methane serves this purpose.• Homogeneously mixed vertically and horizontally we can use

this useful molecule as a thermometer.

Courtesy Glenn Orton

southern winter

southern spring

southern summer


CH4 emission from –80° latitude


Temperatures from 2002-2009


Ethane Spectrum with Missing Features


A Few Project Ideas for IGRINS

• Auroral studies on Jupiter– IGRINS gives access the simultaneous acquisition of H2 and H3

+ emission features.

• Cloud elevation studies on Saturn and Jupiter.• Occultation observations

– Very good probe of CH4 vertical density distribution.

• Comet Observations• Kuiper belt objects probably best left to GMTNIRS

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