Minor Planets and Related Objects. VIII. Deimos

Twelve polarization measurements of Deimos in blue light were obtained at phase angles between 50 and 310. A well-developed negative branch, with minimum polarization approximately - 1.5% near phase angle 110, indicates that Deimos is not bare rock but has a particulate surface layer of dark dust or powder. The phase angle of inversion is 19?5, and the slope of the positive branch is 0.26+0.01% per degree. On the basis of the slope-albedo law for the Moon and the major asteroids, the geometrical albedo of Deimos in blue light should be 0.07+0.01, and the radius 5.4+0.8 km. These values are in good agreement with preliminary Mariner 9 data.