Résumé / Abstract Seminaire_IAP
« Unveiling a pale blue dot: lands, oceans, clouds, vegetation, and spin-obliquity from photometric variation of a directly-imaged second earth »

Yasushi Suto

The earth viewed far away would be identified merely as a pale blue dot, as coined by Carl Sagan. In order to detect possible signatures of the presence of life on a second earth among several terrestrial planets discovered in a habitable zone, one has to develop and establish a methodology to characterize the planet as something beyond
a mere pale blue dot.
We pay particular attention to the periodic change of the color of the planet according to its spin rotation. Because of the large-scale inhomogeneous pattern of the planetary surface, its reflected light comprises different color components corresponding to lands, oceans, ices, and clouds covering the surface of the planet. If one decomposes the color of the dot into several principle components, in turn, one can identify the presence of the different surface components.
Indeed the vegetation on the earth is known to share a remarkable reflection signature; the reflection becomes significantly enhanced at wavelengths longer than 760nm, which is known as a red-edge of the vegetation. If one can identify the corresponding color signature in a pale blue dot, it can be used as a unique probe of the presence of life.
In this talk, I will present two orthogonal approaches to interpret the photometric variation of colors of a second earth; reconstruction of the surface components from the diurnal change, and estimate of the spin rotation period and obliquity from the frequency modulation over planetary orbital period. In particular, I focus on the feasibility of the methodologies for future space missions, and consider the direction towards astrobiology from astronomy.
vendredi 7 septembre 2018 - 11:00
Amphithéâtre Henri Mineur, Institut d'Astrophysique de Paris
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