Abstract
Abstract Even though it was not designed as an exoplanetary research mission, the Deep Space Climate Observatory ( DSCOVR ) has been opportunistically used for a novel experiment in which Earth serves as a proxy exoplanet. More than 2 yr of DSCOVR Earth images were employed to produce time series of multiwavelength, single-point light sources in order to extract information on planetary rotation, cloud patterns, surface type, and orbit around the Sun. In what follows, we assume that these properties of the Earth are unknown and instead attempt to derive them from first principles. These conclusions are then compared with known data about our planet. We also used the DSCOVR data to simulate phase-angle changes, as well as the minimum data collection rate needed to determine the rotation period of an exoplanet. This innovative method of using the time evolution of a multiwavelength, reflected single-point light source can be deployed for retrieving a range of intrinsic properties of an exoplanet around a distant star.
Highlights
An extrasolar planet, or exoplanet, is a planet outside our solar system circling a star other than our Sun
We look for the best factor f so that the resulting signal, which we call the surface-signature radiance (Is), Is = image at 780 nm (I780) - f · image at 388 nm (I388), (3)
While the details will be different for an exoplanet, it is worth noting that, in both the ultraviolet and visible channels, the Earth looks brighter in the southern hemisphere (SH) summer (February 8), when the southern oceans are facing more directly toward the Earth Polychromatic Imaging Camera (EPIC) camera, than in the northern hemisphere (NH) summer (August 8), when the northern landmass is more in the field of view (FOV)
Summary
Exoplanet, is a planet outside our solar system circling a star other than our Sun. When assuming a template reflectance spectra of the major surface types, including ocean, snow, soil, vegetation, and clouds, the EPOXI spectrophotometry can be decomposed to recover the fractions and longitudinal distributions of the various surfaces (Fujii et al 2010, 2011) Despite this progress, the use of Earth images for exoplanet studies has been limited in scope. The use of Earth images for exoplanet studies has been limited in scope It has been suggested repeatedly using theoretical models that Earth’s rotational period can be estimated from its reflected light variations, even in the presence of time-varying clouds (Pallé et al 2008; Oakley & Cash 2009). This study is the first empirical demonstration that intrinsic properties of an Earth-like exoplanet, including the planet’s rotation period and surface and cloud variations, can be determined from reflected light spectrum variations
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