Polarimetric Studies of Solar Light Scattered by Interplanetary Dust Particles and the Eye-Sat Project

Abstract:

Studying intensity and linear polarization of the solar light scattered by interplanetary dust is of interest for various reasons. This so-called zodiacal light constitutes a faint polarized glow that constitutes a changing foreground for observations of faint extended astronomical sources. Besides, analysis of its polarization provides information on properties of the dust particles, such as spatial density, morphology and complex refractive index. Previous observations, mostly from the Earth and with a resolution in the 10° range, have been used to infer that the local polarization at 90° phase angle increases with increasing solar distance. Numerical simulations suggest that, in the inner solar system, interplanetary dust particles consist of a mixture of absorbing and less absorbing materials, and that radial changes originate in a decrease of organic materials with decreasing solar distance under alteration or evaporation processes.

To improve the quality of data on zodiacal light polarimetry, Eye-Sat nanosat is being developed in the context of the JANUS CNES cubesats program for students. The project is now in phase C-D, for a piggy-back launch in 2016. Eye-Sat triple cubesat is anticipated to demonstrate the feasibility of a series of new on-board technologies. Moreover, during its one-year mission, zodiacal light intensity and polarization are to be measured, for the first time with a spatial resolution of about 1° over a wide portion of the sky and in four different wavelengths (visible to near-IR), leading to a better assessment of interplanetary dust properties.

Finally, a significant fraction of the interplanetary dust is estimated to come from comets, the most pristine objects to be found in the inner solar system. While similarities have indeed been noticed between polarimetric properties of interplanetary and cometary dust particles, the latter being currently extensively documented by the Rosetta mission to comet 67P/Churyumov-Gerasimenko, further studies of interplanetary dust should provide a better insight on possible delivery of carbonaceous particles on telluric planets through dust impacts at an epoch of heavy bombardment, and thus to the early solar system evolution.

Support from CNES is warmly acknowledged.