Not much is known about the geology of this world. It's not certain if it even had an atmosphere, as the Spacemen seemed to live in domed cities, implying the atmosphere was either too harsh for them to live in, or that there wasn't one at all. It's also possible that the domes are for protection from meteorological conditions that could endanger the cities, but this is unknown.
The exact location of this asteroid is impossible to determine, but it's not far from Earth, only a few thousand miles away, which means it can't be in the asteroid belt. Chances are, considering the mission to this world happened before the first moon landing, one would assume it can't be much farther than Luna. (keep in mind the mission to the Spacemen Homeworld wasn't actually a landing, it was put in orbit, which is far less complicated, so distance might not have been as big of an issue)
However it should also be noted that there is a strong possibility that the Spacemen Homeworld's orbit can change from time to time, bringing it much closer to Earth at certain points in time. Considering the great distance between Earth and the belt, and the fact that at that time the first manned missions to the Moon, Venus and Mars are still years away, this is a more likely explanation.