For quite a while, Mercury was thought to be tidal locked. You'll find lots of old SF with that "fact". Edit: Until 1965, see http://en.wikipedia.org/wiki/Tida

For quite a while, Mercury was thought to be tidal locked. You'll find lots of old SF with that "fact". Edit: Until 1965, see http://en.wikipedia.org/wiki/Tidal_locking#Planets http://en.wikipedia.org/wiki/Tidal_locking#Planets Edit 2: Check Larry Niven's first published short story. http://en.wikipedia.org/wiki/Larry_Niven#Work http://en.wikipedia.org/wiki/Larry_Niven#Work