https://www.dlr.de/content/en/articles/ ... froth.html
Comet 67P is full of voids and without much cohesion
This reconstruction of events is, in itself, challenging detective work, but the first direct measurement of the consistency of comet ice also provides important insights. The parameters of surface contact showed that this ancient, 4.5-billion-year-old mixture of ice and dust is extraordinarily soft – it is fluffier than the froth on a cappuccino, the foam in a bathtub or the whitecaps of waves meeting the coast. "The mechanical tension that holds the comet ice together in this chunk of dust is just 12 pascal. That is not much more than 'nothing'," explains Jean-Baptiste Vincent, who is studying the compressive and tensile strength of 'primitive' ice. This ice has been stored in comets for 4.5 billion years as if in a cosmic freezer, bearing witness to the earliest period of the Solar System.
The investigation also allowed an estimate of the porosity of the 'rock' touched by Philae. Approximately 75 percent, three quarters of the interior, consists of voids. The 'boulders' omnipresent in the images are thus more comparable to Styrofoam rocks in a film studio fantasy landscape than to real, hard, massive rocks. At another location, a six-metre wide rock, captured in several images, even moved uphill due to the gas pressure of evaporating comet ice.
