Polarimetric Signature of Ocean as Detected by Near-Infrared Earthshine Observations

Context. The discovery of an extrasolar planet with an ocean has crucial importance in the search for life beyond Earth.

The polarimetric detection of specularly reflected light from a smooth liquid surface is anticipated theoretically, though the polarimetric signature of Earth’s ocean has not yet been conclusively detected in disk-integrated planetary light.

Aims. We aim to detect and measure the polarimetric signature of the Earth’s ocean.

Methods. We conducted near-infrared polarimetry for lunar Earthshine and collected data for 32 nights with a variety of ocean fractions in the Earthshine contributing region. Results. A clear positive correlation was revealed between the polarization degree and ocean fraction. We found hourly variations in polarization in accordance with rotational transition of the ocean fraction. The ratios of the variation to the typical polarization degree were as large as ~0.2-1.4.

Conclusions. Our observations provide plausible evidence of the polarimetric signature attributed to Earth’s ocean. Near-infrared polarimetry may be considered a prospective technique for the search for exoplanetary oceans.

J. Takahashi, Y. Itoh, T. Matsuo, Y. Oasa, Y. P. Bach, M. Ishiguro

Comments: Accepted for publication in A&A (21 pages, 13 figures, 3 tables)
Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Atmospheric and Oceanic Physics (physics.ao-ph)
Cite as: arXiv:2106.10099 [astro-ph.EP] (or arXiv:2106.10099v1 [astro-ph.EP] for this version)
Submission history
From: Jun Takahashi
[v1] Fri, 18 Jun 2021 12:48:54 UTC (683 KB)
https://arxiv.org/abs/2106.10099
Astrobiology