Lakes were not found near near Titan's center of Titan which was studied on January 14, 2005. A part of the Huygens-Cassini probe landed there. The pictures taken by the probe as it fell showed no open areas of liquid, but showed rivers that had dried. It was at first thought that dark areas near the center of Titan could be a lake of a liquid or tar-like substance, but the probe landed on the dark area, and it is solid without any liquid. A device known as a penetrometer studied the surface as the probe landed and seemed to find wet clay. Scientists believe that the penetrometer may have landed on a large pebble, and they say that the surface is similar to sand made of ice. Pictures taken after the probe landed show a large flat area covered in pebbles. The pebbles may be made of water ice and are partly rounded, which indicates fluids.