Title:Spectropolarimetric Observations of Earthshine on the Moon
Author(s):Jun Takahashi, Yoichi Itoh, Makoto Sakamoto, Kentaro Matsuda, Katsuyuki Konoshita, Satoshi Iida
Abstract:
We present results of our spectropolarimetric observations of Earthshine on the Moon. Spectropolarimetry of extrasolar planets has been expected to provide their characteristics including astrobiologically important information. Stam (2008) calculates polarization spectrum of light reflected by Earth-like extrasolar planets. This model shows that the existence of atmospheric oxygen in exoplanets will cause an increase of polarization at its absorption bands (e.g. 760nm). It is also noted that the polarization spectrum of a planet is insensitive to the absorption that takes place between the planet and the observer. This means that the ground-based spectropolarimetric observation is a potentially powerful technique for detecting atmospheric oxygen in exoplanets.
For the purpose of assessing the feasibility of spectropolarimetry as a tool for characterizing exoplantes, we have observed Earthshine regarding it as the imitated spatially integrated light from a distant Earth-like planet. The dark side of Crescent Moon has been observed in Nishi-Harima Astronomical Observatory in Hyogo, Japan in December 2008, using a 60cm Cassegrain telescope mounted with the simultaneous polarimetric imager/spectrometer developed by Nishida (2008, master thesis of Kobe University) and other predecessors. In the obtained spectra, possible polarization increase at the 760nm oxygen band has been derived.