The comet currently being observed by the ESA’s Rosetta spacecraft may actually be made entirely of pebbles, scientists involved with the mission explained earlier this week at the 46th annual Lunar and Planetary Science Conference in Houston, Texas.

The CIVA instrument is a suite of six micro-cameras used to capture panoramic pictures of the surface, as well as a spectrometer studies the composition, texture and the albedo (or reflectivity) of samples collected from the comet’s surface. Poulet said that the discovery of the pebbles was a good sign because they match-up with one existing model of how comets form.

That model proposes that miniature particles in the early universe clumped together to form pebbles approximately one-centimeter in size, but that those pebbles did not necessarily grow to be increasingly larger objects. Rather, they come together but retain their original shape, which is what Poulet’s team discovered, indicating that Comet 67P “could be totally made of pebbles.”