Polarimetry of Asteroid 2100 Ra-Shalom at Large Phase Angle

Abstract

Two-color polarimetric observations of C-type asteroid 2100 Ra-Shalom were conducted when its phase angle was 59.7°. No other C-type asteroid has so far been observed at such a large phase angle. We relate the new data point to the available data on C-type asteroids and on Phobos and Deimos and compare the phase curve of these objects with the phase curve of dusty comets. The observed polarization of Ra-Shalom is slightly lower than expected from a common curve of the other C-type asteroids and the martian moons. We conclude that this may be caused by the immature regolith on the surface of this small asteroid.