Arecibo radar observations of Phobos and Deimos

In November 2005, we observed the moons of Mars using the Arecibo 2380-MHz (13-cm) radar, obtaining a result for the OC radar albedo of Phobos (0.056±0.014) consistent with its previously reported radar albedo and implying an upper bound on its near-surface bulk density of 1.6±0.3 g^cm-3. We detected Deimos by radar for the first time, finding its OC radar albedo to be 0.021±0.006, implying an upper bound on its near-surface density of 1.1±0.3 g^cm-3, consistent with a high-porosity regolith. We briefly discuss reasons for these low radar albedos, Deimos' being possibly the lowest of any Solar System body yet observed by radar.