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Spectroscopic Signatures of Terrestrial Exoplanets

Spectroscopic Signatures of Terrestrial Exoplanets. Adam Kraus. What are the expected spectral features of terrestrial exoplanets? What can we learn from them about local conditions and chemistry? What does this imply about design options for future planet-search missions?.

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Spectroscopic Signatures of Terrestrial Exoplanets

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  1. Spectroscopic Signatures of Terrestrial Exoplanets Adam Kraus

  2. What are the expected spectral features of terrestrial exoplanets? • What can we learn from them about local conditions and chemistry? • What does this imply about design options for future planet-search missions?

  3. Signature: Vibrational Transitions • Not all molecules (N2, O2) are IR active • Those of interest: • H2O (Asymmetric Top) • CH4 (Symmetric Top) • N2O (Asymmetric Linear) • CO2 (Symmetric Linear) • Absorption strength => Abundances • Resolution of lines => P, T • Presence => Nonequilibrium chemistry

  4. Infrared Spectra http://www.atmos.umd.edu/~owen/CHPI/IMAGES/transir.html

  5. Signature: Photodissociation • O3 is produced in the upper atmosphere: O + O2 => O3 thus it is a tracer gas. • O3 photodissociates in two bands: • Chappuis band: 440-760 nm • Huggins-Hartley band: 200-360 • Shortward of 300 nm, photodissociation of other molecules absorbs all light

  6. Optical Absorption Spectrum http://daac.gsfc.nasa.gov/CAMPAIGN_DOCS/OCDST/ozone.html

  7. Signature: Broadband Colors • Terrain types like ocean, vegetation, and soil have distinctive albedos and colors: • Ocean: Albedo 5%, blue color • Soil: Albedo 20%, red color • Vegetation: Albedo 20%, green color • On a planet with differentiated terrain, rotation will lead to variability in both color and reflected luminosity

  8. Optical Reflection Spectra http://www.geografforlaget.dk/course/ENGLISH/basic/tele1.htm

  9. TPF: Terrestrial Planet Finder • Goal: Directly observe terrestrial exoplanets • Scheduled to launch in mid-2010s • Two technology choices: • Optical coronagraph • Infrared interferometer

  10. Technology Choice: Coronagraph http://spaceweather.com/glossary/coronagraph.html http://planetquest.jpl.nasa.gov/TPF/tpf_sample.cfm

  11. Technology Choice: Interferometer http://www2.keck.hawaii.edu/geninfo/about.html http://www.svsinc.com/TPF.html

  12. Comparative Benefits • Coronagraph: • Broadband colors (Geography, vegetation) • Optical/NIR spectra (O3, H2O) • Interferometer • NIR/MIR spectra (H2O, CO2, N2O, CH4) • Decision pending the outcome of precursor projects like Kepler and SIM.

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