The opposition surge and photopolarimetry of fresh and coated basalts

We present polarization-phase awe measurements and analysis for three basal t samples: fresh, dark red varnished, and dark gray varnished. Each sample displays a prominent opposition surge, countering the widely held notion th at only particulate surfaces, and not bare rock, will display this phenomen on. The most likely cause of the opposition surge is coherent backscatterin g, but the width of the surge suggests that other mechanisms may also contr ibute. The photopolarimetric properties of the samples; especially the nega tive branch parameters, are most comparable to those of C-class asteroids, (C) 1999 Academic Press.