Astro FOTD

Pluto has ice mountains 3500 meters high. On Earth, once our ice reaches a depth of 30 meters or so, it begins deform continuously by plastic flow - that's why glaciers flow and why there are no tall ice mountains here. Pluto has much weaker gravity, only about 1/12 th of that of Earth, but that's not nearly sufficient to explain the ice mountains - only enough to take them to about 1/10 th their actual height.

The big factor is temperature. The tensile strength of ice increases with decreasing temperature, as fewer and fewer of the hydrogen bonds are disrupted by thermal motion, and at Pluto's -230 C, water ice is a pretty hard rock.

Phil Plait has a nice picture at:


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