The Study of Climate on Alien Worlds
Characterizing atmospheres beyond our Solar System is now within our reach
Experimentally, 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.
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