Ooooo, cool caveats, Hawksguard. Porklet, if you need things to be AS THOUGH the circumference were half that of Earth, how about if you leave it earth-sized, and make your people (and critters, and plants) twice the size? :-) I mean, that has its own problems, but at ~6ft tall humans aren't at the theoretical limit of bio structures, right? Time could be local, with twenty-four (or whatever desired) parts of whatever the rotation period needs to be.

Or hmmmm..... core has more lead than iron (pick magnetically inert heavy-ish metal), atmosphere is denser than earth's, yadda, yadda. Or it outgases nitrogen and oxy at a rate that makes up for increased loss from somewhat lower grav..... there's AlWaYs rationalizations, even if they may not be proven rational, ifyaknowwhattImean.

What have you done? Created parameters for a delightfully complex puzzle. If it gets to be a harder puzzle than you wanted, cheat. Or redefine success. :-)