The atmospheric pressure on VENUS makes it hotter. Although this is something you should learn in school, it is also readily available on the internet. Also, I have a belief that the left time portal in the VOG raid is mercury and not mars. The crucible match on Mercury is in ancient vex architecture which looks identical to that on VENUS. Also the grimoire suggests that the vex previously inhabited Mercury. That then leads to believe that Mercury is past and VENUS is future.