It has been a while since I have done any of the "Science of ..." blogs and my apologies for anyone that was enjoying them but I simply ran out of material as DC canceled it science based books or I stopped reading them. One new series which I have picked up is Warlord of Mars: Dejah Thoris, which was surpirsingly good for me despite how little clothing Dejah wears ... but ... the problem which I have with it is that the science which is used is some of the same bad science which was used in the original novels and has never been rectified.
Back to gravity though and the other problem becomes apparent. Mars has less gravity than Earth and thus when John Carter shows up there he is a superhuman. This might have an aspect of truth in comparison, but think about how humans appeared on the moon. They could not really walk like on Earth because gravity didn't pull them back fast enough to do so (the moon has 1/6th of Earth's gravity). Granted Mars would have more gravity than the Moon but essentially based on the way that we walk, gravity would allow us to either run or jump long distances, not both. The other concept related to gravity is super-strength. In the most recent story arc Dejah is captured by some aliens from Titan (the moon of Saturn) and jailed there. She and a fellow prisoner make a plan to break down the gate which will only be strong enough to hold a Titanian (Titanite?). Even if the character did exhibit some added strength because their muscles were used to working in a higher gravity environment they would likely still not be able to break down a steel gate. The reason is that steel is held together by molecular bonds, not by gravity, and the bonds of any compound (including alloys) is going to be the same throughout the universe at the same pressure and temperature (and assuming that Dejah can still breathe and not freeze to death or be too hot that these are relatively the same.) Thus her super strength wouldn't help her in this instance, nor would a lot of John Carter's help him on Mars.