Zodiacal light, certitudes and questions

Progress achieved in zodiacal light studies not only allows the estimation of the brightness and polarization to be expected in a given direction for an observer in the ecliptic plane; it also provides information about the radial dependence of some local optical properties, and about their phase curves. It is nevertheless necessary to stress the high level of the uncertainties, with, as an example, a value of (0.15 ± 0.08) derived from two approaches for the local geometric albedo at the Earth. Besides, various open questions remain, possibly because of the lack of space observations since the early eighties. This paper would like to warn the reader against crude extrapolations of the available results; it also emphasizes the need for further observations and new computational tools, and presents new laboratory measurements, such as the microgravity series of experiments now under development.