Titan's elusive clouds seen in polarization

Titan, the enigmatic large moon of Saturn, is the unique satellite of the solar system surrounded by a dense atmosphere which has a significant effect on radiation polarization. The Cassini exploration of the kronian system has also revealed the existence of large bodies of liquid at the surface of Titan. It is well known that smooth surfaces polarize the reflected electromagnetic waves, that aspect reinforces the interest of a polarimetric study of the Saturn main satellite. On board the Cassini probe, the ISS (Imaging Science Subsystem) instrument was equipped with a large set of spectral and polarized filters that could be combined with one another.

By using near infrared filters together with polarized filters, we have searched for features highlighted by polarimetric observations, we have targeted both the surface and the atmosphere. We first worked at the near-infrared wavelength of 939 nm, at which the atmosphere of Titan is slightly transparent. The spectral filter CB3 is then employed with two polarization filters, with perpendicular direction. The resulting polarization maps are interpreted with the help of a multidimensional Monte-Carlo radiative transfer model specifically adapted to Titan’s atmosphere.