A 30-m wide boulder with a mass of almost 13,000 tonnes was found to have moved about 140 m across the face of Comet 67P/Churyumov–Gerasimenko in the months before the comet reached perihelion in August, 2015. That was when the when the comet’s activity was at its highest. In both images above, an arrow points to the boulder; in the right-hand image, the dotted circle outlines the original location of the boulder for reference. The rock was probably moved by jets of material outgassing from the comet.
Image Credit: ESA