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The Study of Climate on Alien Worlds

Characterizing atmospheres beyond our Solar System is now within our reach

Kevin Heng

Better Telescopes

2012-07HengF7.jpgClick to Enlarge ImageExperimentally, the next leap is to build dedicated, space-based telescopes capable of measuring high-resolution spectra of exoplanets over protracted periods of time. Astronomers around the world are mobilizing to launch such missions as the Exoplanet Characterization Observatory (EChO) and the Fast Infrared Exoplanet Spectroscopy Survey Explorer (FINESSE), as proposed to the European Space Agency (ESA) and the National Aeronautics and Space Agency (NASA), respectively. If and when these missions—or their successors—eventually fly (in the next decade or two), they will deliver a bounty of both spectral and temporal information on hundreds of exoplanets, from which we may infer their atmospheric chemistry, dynamics and climates. With a richly sampled data set of the emitted light from point-source exoplanets over time, one may construct a power spectrum that elucidates the characteristic time scales on which an exoplanet is flickering, indicating changes in temperature. Such a power spectrum of the atmosphere has been spectacularly constructed for the Earth’s surface, spanning time scales of under a day (diurnal variations) to many millennia (called Milankovitch cycles, and inferred from the geological record). Certainly, space missions are saddled with demands that will not allow for the construction of power spectra on time scales longer than a few months, but it is likely that many of the characteristic peaks in the power spectra will be compressed into a shorter time span for close-in exoplanets such as hot Jupiters and super Earths.

The onus is on the theoretical community to lay down the foundation for understanding the climates of point-source exoplanets in general, thus moving us a step closer toward making more robust statements about their habitability.


  • Burrows, A., et al. 1997. A nongray theory of extrasolar giant planets and brown dwarfs. Astrophysical Journal 491:856–875.
  • Charbonneau, D., et al. 2009. A super-Earth transiting a nearby low-mass star. Nature 462:891–894.
  • Fortney, J. J., et al. 2010. Transmission spectra of three-dimensional hot Jupiter model atmospheres. Astrophysical Journal 709:1396–1406.
  • Guillot, T., and A. P. Showman. 2002. Evolution of 51 Pegasus b-like planets. Astronomy & Astrophysics 385:156–165.
  • Held, I. M. 2005. The gap between simulation and understanding in climate modeling. Bulletin of the American Meteorological Society 86:1609–1614.
  • Heng, K., D. M. W. Frierson and P. J. Phillipps. 2011. Atmospheric circulation of tidally locked exoplanets: II. Dual-band radiative transfer and convective adjustment. Monthly Notices of the Royal Astronomical Society 418:2669–2696.
  • Heng, K., W. Hayek, F. Pont and D. K. Sing. 2012. On the effects of clouds and hazes in the atmospheres of hot Jupiters: Semi-analytical temperature-pressure profiles. Monthly Notices of the Royal Astronomical Society 420:20–36.
  • Heng, K., K. Menou and P. J. Phillipps. 2011. Atmospheric circulation of tidally locked exoplanets: A suite of benchmark tests for dynamical solvers. Monthly Notices of the Royal Astronomical Society 413:2380–2402.
  • Knutson, H. A., et al. 2007. A map of the day-night contrast of the extrasolar planet HD 189733b. Nature 447:183–186.
  • Madhusudhan, N., et al. 2011. A high C/O ratio and weak thermal inversion in the atmosphere of exoplanet WASP-12b. Nature 469:64–67.
  • PeixÓto, J. P., and A. H. Oort. 1984. Physics of climate. Reviews of Modern Physics 56:365–429.
  • Pierrehumbert, R. T. 2010. Principles of Planetary Climate. New York: Cambridge University Press.
  • Seager, S., and D. D. Sasselov. 2000. Theoretical transmission spectra during extrasolar giant planet transits. Astrophysical Journal 537:916–921.
  • Seager, S. 2010. Exoplanet Atmospheres. New Jersey: Princeton University Press.
  • Showman, A. P., and T. Guillot. 2002. Atmospheric circulation and tides of 51 Pegasus b-like planets. Astronomy & Astrophysics 385:166–180.
  • Showman, A. P., and L. M. Polvani. 2011. Equatorial superrotation on tidally locked exoplanets. Astrophysical Journal 738:71–94.
  • Showman, A. P., et al. 2009. Atmospheric circulation of hot Jupiters: Coupled radiative-dynamical general circulation model simulations of HD 189733b and HD 209458b. Astrophysical Journal 699:564–584.
  • Sing, D. K., et al. 2011. Hubble Space Telescope transmission spectroscopy of the exoplanet HD 189733b: High-altitude atmospheric haze in the optical and near-ultraviolet with STIS. Monthly Notices of the Royal Astronomical Society 416:1443–1455.
  • Snellen, I. A. G., R. J. de Kok, E. J. W. de Mooij and S. Albrecht. 2010. The orbital motion, absolute mass and high-altitude winds of exoplanet HD 209458b. Nature 465:1049–1051.
  • Tarter, J., et al. 2007. A reappraisal of the habitability of planets around M dwarf stars. Astrobiology 7:30–65.

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