noon
As far as its size went , it could be classified as `` Earth type , '' but size was almost the only resemblance to Earth . It orbited in space some five hundred and fifty million miles from its Sol-like parent -- a little farther away from the primary than Jupiter is from Sol itself . It was cold there -- terribly cold . At high noon on the equator , the temperature reached a sweltering 180 ° absolute ; it became somewhat chillier toward the poles . H _ -LCB- 2 -RCB- O was , anywhere on the planet , a whitish , crystalline mineral suitable for building material . The atmosphere was similar to that of Jupiter , although the proportions of methane , ammonia , and hydrogen were different because of the lower gravitational potential of the planet . It had managed to retain a great deal more hydrogen in its atmosphere than Earth had because of the fact that the average thermal velocity of the molecules was much lower .