The “Spectral Zoo” of Exoplanet Atmospheres

  • Aki Roberge
  • Sara Seager
Living reference work entry


The great abundance of exoplanets and the unexpectedly wide range of their bulk properties create a huge realm of possibilities in exoplanet atmospheres. Opportunities for atmospheric characterization of other worlds abound, as well as pitfalls for the unwary. In this chapter, we make a first foray into exploring the richness of exoplanet atmospheres, with a tour of the exoplanet “spectral zoo.” We then follow the path of light from a star onto an exoplanet and to a distant spectrograph; the details of what happens to that light within the planet’s atmosphere will be discussed in other chapters. We briefly discuss how the light is then affected by the spectrograph and recorded by a detector, resulting in an observed planet spectrum. As will be seen, one of the major challenges for measuring the effects of a planet’s atmosphere in an observed spectrum is disentangling them from effects caused by the instrumentation used to acquire that spectrum. We conclude with a few thoughts on general strategies to overcome observational challenges and harvest the best science from the treasure trove of exoplanets we can and will study in the coming decades.


Exoplanet Atmosphere Spectroscopy 



A.R. acknowledges support by the NASA Astrobiology Program, through the Goddard Center for Astrobiology and the Nexus for Exoplanet System Science (NExSS) research coordination network.


  1. Cahoy KL, Marley MS, Fortney JJ (2010) Exoplanet albedo spectra and colors as a function of planet phase, separation, and metallicity. ApJ 724:189–214ADSCrossRefGoogle Scholar
  2. Christensen PR, Pearl JC (1997) Initial data from the Mars global surveyor thermal emission spectrometer experiment: observations of the Earth. J Geophys Res 102:10875–10880ADSCrossRefGoogle Scholar
  3. Dyudina U, Zhang X, Li L et al (2016) Reflected light curves, spherical and bond albedos of Jupiter- and Saturn-like exoplanets. ApJ 822:76ADSCrossRefGoogle Scholar
  4. Hu R, Seager S (2014) Photochemistry in terrestrial exoplanet atmospheres. III. Photochemistry and thermochemistry in thick atmospheres on super Earths and mini Neptunes. ApJ 784:63Google Scholar
  5. Kaltenegger L, Traub WA (2009) Transits of Earth-like planets. ApJ 698:519–527ADSCrossRefGoogle Scholar
  6. Karkoschka E (1998) Methane, ammonia, and temperature measurements of the Jovian planets and Titan from CCD-spectrophotometry. Icarus 133:134–146ADSCrossRefGoogle Scholar
  7. Knutson HA, Charbonneau D, Noyes RW, Brown TM, Gilliland RL (2007) Using stellar limb-darkening to refine the properties of HD 209458b. ApJ 655:564–575ADSCrossRefGoogle Scholar
  8. Kreidberg L, Bean JL, Désert JM et al (2014) Clouds in the atmosphere of the super-Earth exoplanet GJ1214b. Nature 505:69–72ADSCrossRefGoogle Scholar
  9. Mandel K, Agol E (2002) Analytic light curves for planetary transit searches. ApJ 580:L171–L175ADSCrossRefGoogle Scholar
  10. Mayorga LC, Jackiewicz J, Rages K et al (2016) Jupiter’s phase variations from Cassini: a testbed for future direct-imaging missions. AJ 152:209ADSCrossRefGoogle Scholar
  11. Nayak M, Lupu R, Marley MS et al (2017) Atmospheric retrieval for direct imaging spectroscopy of gas giants in reflected light. II. Orbital phase and planetary radius. PASP 129(3):034401ADSCrossRefGoogle Scholar
  12. Roberge A, Rizzo MJ, Lincowski AP et al (2017) Finding the needles in the haystacks: high-fidelity models of the modern and Archean solar system for simulating exoplanet observations. PASP 129:124401ADSCrossRefGoogle Scholar
  13. Robinson TD, Meadows VS, Crisp D et al (2011) Earth as an extrasolar planet: Earth model validation using EPOXI Earth observations. Astrobiology 11:393–408ADSCrossRefGoogle Scholar
  14. Robinson TD, Ennico K, Meadows VS et al (2014) Detection of ocean glint and ozone absorption using LCROSS Earth observations. ApJ 787:171ADSCrossRefGoogle Scholar
  15. Seager S (2010) Exoplanet atmospheres: physical processes. Princeton University Press, PrincetonGoogle Scholar
  16. Seager S, Sasselov DD (2000) Theoretical transmission spectra during extrasolar giant planet transits. ApJ 537:916–921ADSCrossRefGoogle Scholar
  17. Wakeford HR, Sing DK, Kataria T et al (2017) HAT-P-26b: a Neptune-mass exoplanet with a well-constrained heavy element abundance. Science 356:628–631ADSCrossRefGoogle Scholar

Copyright information

© This is a U.S. Government work and not under copyright protection in the US; foreign copyright protection may apply 2018

Authors and Affiliations

  1. 1.Exoplanets and Stellar Astrophysics LabNASA Goddard Space Flight CenterGreenbeltUSA
  2. 2.Department of Earth, Atmospheric and Planetary SciencesMassachusetts Institute of TechnologyCambridgeUSA

Section editors and affiliations

  • Sara Seager
    • 1
  1. 1.Department of Earth, Atmospheric and Planetary SciencesMassachusetts Institute of TechnologyCambridgeUSA

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