Searching for water earths in the near-infrared
Document ID: 264
Zugger, Michael E.1,2
Kasting, James F.2,3
Williams, Darren M.2,4
Kane, Timothy J.1,3
Philbrick, C. Russell5
1 The Pennsylvania State University, Applied Research Laboratory, University Park, PA, U.S.A.
2 The Pennsylvania State University, Center for Exoplanets and Habitable Worlds, University Park, PA, U.S.A.
3 The Pennsylvania State University, Department of Geosciences, University Park, PA, U.S.A.
4 School of Science, Penn State Erie, The Behrend College, Erie, PA, U.S.A.
5 North Carolina State University, Department of Physics, Raleigh, NC, U.S.A.
Abstract
Over 500 extrasolar planets (exoplanets) have now been discovered, but only a handful are small enough that they might be rocky terrestrial planets like Venus, Earth, and Mars. Recently, it has been proposed that observations of variability in scattered light (both polarized and total flux) from such terrestrial-sized exoplanets could be used to determine if they possess large surface oceans, an important indicator of potential habitability. Observing such oceans at visible wavelengths would be difficult, however, in part because of obscuration by atmospheric scattering. Here, we investigate whether observations performed in the near-infrared (NIR), where Rayleigh scattering is reduced, could improve the detectability of exoplanet oceans. We model two wavebands of the NIR which are "window regions" for an Earth-like atmosphere: 1.55-1.75 μm and 2.1-2.3 μm. Our model confirms that obscuration in these bands from Rayleigh scattering is very low, but aerosols are generally the limiting factor throughout the wavelength range for Earth-like atmospheres. As a result, observations at NIR wavelengths are significantly better at detecting oceans than those at visible wavelengths only when aerosols are very thin by Earth standards. Clouds further dilute the ocean reflection signature. Hence, other techniques, e.g., time-resolved color photometry, may be more effective in the search for liquid water on exoplanet surfaces. Observing an exo-Earth at NIR wavelengths does open the possibility of detecting water vapor or other absorbers in the atmosphere, by comparing scattered light in window regions to that in absorption bands.
Keywords: numerical methods, planets and satellites: atmospheres, planets and satellites: detection, planets and satellites: surfaces, polarization, radiative transfer
| Citation: | "Searching for water earths in the near-infrared", Zugger, M. E., J. F. Kasting, D. M. Williams, T. J. Kane, C. R. Philbrick, The Astrophysical Journal, Vol. 739, Number 1, The American Astronomical Society, August 2011, pp. 1 - 5, DOI: 10.1088/0004-637X/739/1/12 |