Close-up images of the final Philae landing site on comet 67P/Churyumov-Gerasimenko acquired by the ROLIS camera

摘要

After coming to rest on the night side of comet 67P/Churyumov-Gerasimenko,the ROLIS camera on-board Rosetta's Philae lander acquired five images of thesurface below the lander, four of which were with the aid of LED illuminationof different colors. The images confirm that Philae was perched on a slopedsurface. A local horizon is visible in one corner of the image, beyond which wecan see the coma. Having spent a full day on the surface Philae was commandedto lift and rotate, after which a final, sixth, LED image was acquired. Thechange in perspective allowed us to construct a shape model of the surface. Thedistance to the foreground was about 80 cm, much larger than the nominal 30 cm.This caused stray light, rather than directly reflected LED light, to dominatethe image signal, complicating the analysis. The images show a lumpy surfacewith a roughness of apparently fractal nature. Its appearance is completelydifferent from that of the first landing site, which was characterized bycentimeter to meter-sized debris (Mottola et al., 2015). We recognize neitherparticles nor pores at the image resolution of 0.8 mm per pixel and large colorvariations are absent. The surface has a bi-modal brightness distribution thatcan be interpreted in terms of the degree of consolidation, a hypothesis thatwe support with experimental evidence. We propose the surface below the landerto consist of smooth, cracked plates with unconsolidated edges, similar toterrain seen in CIVA images.