Although there were a number of aberrant planetary designations over the years, most of the gates visited in SG-1 seem to fall into three categories;
- P names (for Planets)
- M names (for Moons).
- X names (for uneXplored)
Assuming KS7-535 follows the same pattern, it's possible that it was a Kuiper-belt object (e.g. like Pluto). This would also explain the extremely cold temperature given its extreme distance from its local star.
As @BESW has pointed out in his comment, this naming scheme was frequently ignored/forgotten about by the writers, then utterly subverted in Stargate Atlantis when the writers gave all of the destinations in the Pegasus Galaxy "M" designations regardless of whether they were moons or planets.
Unfortunately, this appears to be one of those cases where Bellisario's Maxim applies. Close examination reveals a lack of consistency on the part of those making the show.