62th Ohio State University Symposium on Molecular Spectroscopy June 18–22, 2007 RECENT...

62th Ohio State University Symposium on Molecular Spectroscopy • June 18–22, 2007

RECENT APPLICATIONS AND FUTURE PROSPECTS OF METHANE

SPECTROSCOPY TO THE ATMOSPHERE OF TITAN

RECENT APPLICATIONS AND FUTURE PROSPECTS OF METHANE

SPECTROSCOPY TO THE ATMOSPHERE OF TITAN

Vincent BOUDONInstitut Carnot de Bourgogne – UMR 5209 CNRS-Université de Bourgogne, 9 Av. A. Savary, BP 47870, F-21078 DIJON, France

Athéna COUSTENIS, Emmanuel LELLOUCH, Pierre DROSSARTLESIA, Observatoire de Paris-Meudon, 5 Place Jules Jansen, F-92195 MEUDON, France

Alberto NEGRÃOObservatorio Astronomico and Faculdade de Ciências da Universidade de Lisboa, 1749-016, LISBOA, Portugal

Caitlin A. GRIFFITHLunar and Planetary Laboratory, University of Arizona, TUCSON, AZ 85721, USA


ContentsContents

I. Methane on Titan

II. Status of CH4 spectroscopy

III. Application of the octad’s modeling

IV. Perspectives for CH4 spectroscopy


I. Methane on TitanI. Methane on Titan


Titan: Methane everywhere!Titan: Methane everywhere!

Lakes

Rivers Cryovolcanoes?

Clouds

Atmosphere

Soil (clathrates?)


DISR spectrum of Titan (Huygens / ESA)DISR spectrum of Titan (Huygens / ESA)2.0

1.5

1.0

0.5

0.01.61.41.21.00.8

/ Wavelengthμm

12000 10000 9000 8000 7000 6000 / Wavenumber cm-1

= , = 30 Target Sun Altitude km


Use of CH4 spectroscopy on TitanUse of CH4 spectroscopy on Titan• Measure methane concentration (1.6 % stratosphere, 5 % ground)

• Determine methane’s origin

• Retrieve methane vertical profiles

• Remove methane spectrum to find minor species

• Retrieve haze profile

• Measure surface albedo

Visible 939 nm


II. Status of CH4 spectroscopyII. Status of CH4 spectroscopy


The polyads of CH4The polyads of CH4

« Saturn Methane Image » – 16/02/2004

Cassini / MT2 Filter : 727 nm = 13755 cm-1

Global fit

Titan

939 nm CH4 window

1.5

1.0

0.5

0.0

1200

011

000

1000

090

0080

0070

0060

00 /

Wavenumber

cm-1


Present status of CH4 analyses (early 2007)Present status of CH4 analyses (early 2007)

Polyad / Spectral region Line positions Line intensities Line shapes

1 – Ground state

0–200 cm-1 (> 5.0 μm)

Complete analysis,

J ≤ 24Complete analysis No analysis

2 – Dyad

1000–1800 cm-1 (5.6–10.0 μm)

Complete analysis,

J ≤ 23Complete analysis,

with some hot bands

Perturbers:

He et N2

3 – Pentad

2200–3300 cm-1 (3.0–4.6 μm)

Complete analysis,


cold bands only

Perturbers:

He, Ar, N2, O2, CH4

4 – Octad

3700–4800 cm-1 (2.0–2.7 μm)

Complete analysis,


cold bands onlyNo analysis

5 – Tetradecad

5400–6300 cm-1 (1.6–1.9 μm)

Incomplete analysis,

J ≤ 10Partial analysis, cold

bands onlyNo analysis

6 – Icosad

6600–7700 cm-1 (1.3 – 1.5 μm)Very partial analysis of 1 band among 20

No analysis No analysis

Upper polyads

> 7800 cm-1 (< 1.28 μm)No analysis No analysis No analysis

Windows

(polyad far wings, all regions)No analysis No analysis No analysis


III. Application of the octad’s modelingIII. Application of the octad’s modeling


3 μm region with ISO spectra 3 μm region with ISO spectra12CH4 + 13CH4 + 12CH3D absorption coefficients calculated thanks to Dijon analyses

Modeling of ISO (and Keck II) data, including haze profile


Surface albedo from CFHT/FTS spectraSurface albedo from CFHT/FTS spectra

2

2 μm window


VLT/NACO spectrum of Huygens site (I)VLT/NACO spectrum of Huygens site (I)

A. Negrão, M. Hirtzig, A. Coustenis,E. Gendron, P. Drossart, P. Rannou,M. Combes and V. Boudon,J. Geophys. Res. Planets 112, E02S92 (2007)

VLT (NAOS/CONICA image)January 16, 2005

Huygens landing site

Bright region

Darkregion

NB: Measurement error(3) above 2.12 μm is ± 27 %


VLT/NACO spectrum of Huygens site (II)VLT/NACO spectrum of Huygens site (II)

A. Negrão, M. Hirtzig, A. Coustenis, E. Gendron, P. Drossart, P. Rannou, M. Combes and V. Boudon,J. Geophys. Res. Planets 112, E02S92 (2007)

(Irwin = « band » model)


Discovery of a polar ethane cloudDiscovery of a polar ethane cloud

C. A. Griffith, P. Penteado, P. Rannou,R. Brown, V. Boudon, K. H. Baines,R. Clark, P. Drossart, B. Buratti,P. Nicholson, C. P. McKay, A. Coustenis, A. Negrão and R. Jaumann,Science 313, 1620–1622 (2006)

Octad

2.11 μm

2.17 μm


IV. Perspectives for CH4 spectroscopyIV. Perspectives for CH4 spectroscopy


Spectroscopy of CH4: what next?Spectroscopy of CH4: what next?

•Continue the global analysis approach

•Next goal: the Tetradecad (5400 – 6300 cm-1)

•Add new data (positions & intensities, hot bands)

•Windows (high J, far wings)

New approches :New approches :

•Use of the ab initio potential energy surface to calculate the effective Hamiltionian and dipole moment (cf. work of Vl. G. Tyuterev, Reims, France)

•Statistical approach for hot bands


The triacontadThe triacontadSpectre : L. R. Brown (JPL/KPNO)

1.5

1.0

0.5

0.0920090008800860084008200

/ Wavenumber cm-1

DISR


The STDS database

The STDS database

Spherical Top Data System

www.u-bourgogne.fr/LPUB/shTDS.html

• Molecular parameter database

• Calculation and analysis programs

• XTDS : Java interface


Post-doctoral postition available in Dijon!Post-doctoral postition available in Dijon!

Modelling of methane absorption in the near infrared region and application to planetary atmospheres

12 months position

Contact:

[email protected]

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62th Ohio State University Symposium on Molecular Spectroscopy June 18–22, 2007 RECENT...

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