The only world currently settled in Tychus, Yellow Sky (G2/R2/ A2-3/P3-4/H3) presents a very strange dichotomy of environments. Eons ago, a series of massive impacts raised a belt of vast highlands across the planet’s major continent. Averaging 6 to B kilometers above sea level, these highlands are generally tolerable to humans. However, the lower altitudes rapidly become uninhabitable due to heavy concentrations of chlorine and carbon dioxide, and the atmosphere soon becomes uncomfortably thick. This divides Yellow Sky into two distinct biospheres: an oxygen-breathing, Series I biosphere on the high plateaus, and a chlorine-breathing, Series III biosphere in the hot, swampy lowlands.
The old Orlamu settlement of Mount Illumination is still the center of the colony, and therefore the Tychus system. It’s a town of about 5,000 people. Hundreds of contractors and local laborers are busy changing the landscape, extensively improving the town’s spaceport, industrial base, and government buildings. The remainder of Yellow Sky’s 20,000 colonists live all over the highlands-some in isolated farms dozens of kilometers from their nearest neighbor. Almost 1,000 of Yellow Sky’s colonists are weren who accompanied their Orlamu patrons to this world. They easily adjusted to the lack of technology imposed by the Long Silence, and they flourished in the interregnum.
Deep in the chlorine-choked swamps of Yellow Sky’s lowlands lies a world full of alien ruins. Black monoliths of stone and forgotten cities mired in mud rise from the green mists, hinting at a Precursor race long vanished. It seems that this forgotten species possessed an advanced technology that replaced metallurgy with complex enzyme and biochemical reactions. Since open flame can’t burn in the chlorine-thick atmosphere of Yellow Sky’s lower altitudes, the locals call this ancient species the Stoneburners.
The original Orlamu settlers had every intention of surveying these ruins as soon as Mount Illumination was on its feet, but a lack of breathing gear and e-suits prevented them from venturing into the lowlands during the Long Silence. Consequently, scientists and xenoarcheologists are only now beginning serious explorations of the Stonebuner sites.
The lowlands of Yellow Sky are a dangerous place. The environment is potentially deadly to a human expedition, and very little is known of the plants and animals that inhabit these regions (again, the Orlamu settlers intended to explore the lowlands generations ago but simply lacked the hardware). Of the dozen expeditions mounted to Stonebuner sites so far, three have failed to return. The others report mixed success: While four expeditions brought back both plant and animal samples, only one recorded the details of a Stonebuner site. Five expeditions had to turn hack due to equipment failure; the atmosphere and the swamp waters are both more corrosive than was initially thought.