Edited. It's caused by stress from Jupiter's gravity. I typed too fast without checking... my bad.
Also, regarding titan, there are liquid lakes of methane which could hold life, as crazy as that may be.
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Why is that crazy? Also, they're planets not "moon"
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Europa and titan are moons... of Jupiter and Saturn respectively. And methane based life is a little bit of a leap considering we only know of water based life.