Using Earth as an example, how much less gravity could the planet exert and still retain its atmosphere and oceans? Or is it a matter of size, mass, magnetosphere, place in the solar system, all of the above?

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    $\begingroup$ Venus has only 90% of earth's surface gravity, but a MUCH denser atmosphere, so it is likely that there isn't a simple linear relationship between surface gravity and atmospheric characteristics. $\endgroup$ – David White Apr 30 at 19:22
  • $\begingroup$ @DavidWhite But in Venus case isn't that more because of the tremendous heat creating great pressure? $\endgroup$ – Len May 1 at 1:14
  • $\begingroup$ That heat is no doubt the result of the high atmospheric density preventing IR radiation from escaping to outer space. So it's the pressure that causes the heat, not the other way around. $\endgroup$ – David White May 1 at 3:03

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