The Deseret System includes a hot F5 system primary star, and seven planets. The outer five of these are gas giants, two of which have moons large enough to be of interest for very minor human settlement in the form of research or mining colonies. The inner two are rocky worlds, the inmost of which is a scorched, airless rock similar to Mercury. The second planet is the most populated, a desert world with a few lakes in low-lying depressions, around which irrigation agriculture is a major industry. Mining settlements scattered in the rocky and sandy deserts around these fertile lowlands produce metals and ceramics for export, as well as hosting large solar power facilities. The planet has two moons, both of which are military reservations hosting protected command centers for the orbital defense network.
Deseret was a minor Drakat outpost (and thus with a Drakat name not easily transliterated into English) conquered by the Earth Federation in the late 2160's. Around the same time that the Third Vatican Catholic sect was sending colonists to nearby St. Michael's Star, a group of Mormon Fundamentalists who favored polygamy and theocracy bought out the colonization rights and began human settlement on what was renamed Deseret. Founding their capital of Port Joseph Smith on a fertile lowland area near one of the rare lakes on this driest of human colony worlds, they began to prosper. However, a Bug attack in early 2194 very nearly overran the colony, and the decimated survivors began seeking new settlers who were not necessarily Mormons.
The population today of 30 million people is only about 10 percent Mormon or Mormon Fundamentalist, and is scattered over dozens of settlements, mostly involved with agriculture in the fertile lowlands or mining in the open desert areas. Two million people live in Port Joseph Smith, still the capital and largest settlement. Ongoing efforts to terraform the planet to increase the water content of the ecosphere include a program to crash water-rich comets onto an enormous Impact Zone, a rectangle four thousand miles long and a thousand miles wide along the planet's equator opposite the capital. No settlements or human activity is allowed in the Impact Zone, for obvious reasons.
Behind the Scenes
The planet is of course named for the original Mormon colony in Utah. Not only is this a reference to the Port Joe Smith incident in the Starship Troopers movie, but Marcus is an avid student of Mormon military history and theology in general (mostly to debunk it, but then he's not a complete idiot).