When the Rosetta spacecraft entered orbit around comet 67P/Churyumov-Gerasimenko, first images captured deep circular depressions among the other surface features.  Now that the orbiter has taken significant observations of the comet’s surface, the science team has concluded that these depressions are actually sinkholes that form by the same processes that form sinkholes 500 Million kilometers away here on Earth. Sinkholes on Earth form when subsurface material is eroded away.  Though not initially visible on the surface, the material falls deep underground leaving a circular cavern.  Once enough material has eroded away, the top of the cavern collapses, leaving a large...