Comparative Climatology III 2018 (LPI Contrib. No. 2065) 2058.pdf

USING DEEP SPACE CLIMATE OBSERVATORY (DSCOVR) MEASUREMENTS TO STUDY THE EARTH AS AN EXOPLANET. Jonathan H. Jiang, Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California ([email protected])

Motivation: In the famous photograph of Significance: This method of using the time planet Earth taken by the Voyager 1 spacecraft evolution of a multi-wavelength, reflected single- from 6 billion kilometers away on February 14, point light source, can be deployed for retrieving 1990, the Earth appears as a single-point light, a a range of intrinsic properties of an exoplanet Pale-Blue Dot. However, the use of Earth images around a distant star. Pontential applications in- for exoplanet studies has been limited in scope. clude using measurements from the soon-to-be Theoretical models have suggested that infor- launched JWST and future WFrist experiments mation about Earth’s rotational period and surface and thus contribute to exoplanet research. properties may be obtained from variations of its References: Jiang, J.H. et al. Using Deep reflected light. Empirically testing this idea re- Space Climate Observatory Measurements to quires observations of a long temporal baseline. Study the Earth as An Exoplanet, Astronomical Data and Results: More than two years of Journal, in press, 2018.. Earth images taken from L1 point by DSCOVR Acknowledgement: This work was partly spacecraft are used to produce time series of mul- supported by a Exoplanet Study Initiative at the ti-wavelength, single-point light sources, in order Jet Propulsion Laboratory, California Institute of to extract information on planetary rotation, Technology weather and cloud patterns, surface type (ocean, land, vegetation), 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 conclu- sions are then compared with known data about our planet. We further simulated phase angle changes, as well as the minimum data collection rate needed to determine the rotation period of an exoplanet.

Top: DSCOVR 10 wavelength imagery of the Earth taken at 9:22 UTC, February 8, 2017; Bottom: Fourier series power spectra of the Earth’s 551 nm single-point reflected lights reveal information about the Earth rotation and orbital periods, as well as surface features.