Zar'siel I

Zar'siel I is the secondary world of the newly-founded Zar'siel Sept of the T'au Empire. It is a slightly smaller than average terrestrial planet falling within the 'earth-like' classification and found in the Koronus Expanse, more specifically in the Accursed Demesne sub-sector.

History
Zar'siel I, thus named for its position relative to the star within the Zar'siel system, was the second planet explored by the T'au expedition into the far reaches of the Koronus Expanse. As with Zar'siel II, it was discovered in a maiden state where no signs of local civilization or colonization by another space-faring specie existed.

Zar'siel II is an hostile world that, while habitable, is highly hostile to life. Only a small amount of colonists were stationed there by the T'au Sept, which was considered a necessary evil as the planet was abundantly rich in the mineral resources which the Prime world of the Sept sorely lacked. As such, mineral shipments from the planet are the main interest and purpose of the colony.

Stellar Characteristics
Zar'siel I is the nearest planet on a stable orbit around the binary white stars at the center of its system. The peculiar arrangement of the system allowed two orbits to be stable within its habitable band, however, Zar'siel I is situated at 2.79 AU of the barycenter, just barely on the inner edge of the zone. As such, temperatures are extremely hot on the surface and the quantity of radiations bombarding the planet are much higher.

The atmosphere is primarily a viable Oxygen-Nitrogen mix, however its upper strata is obscured by a certain quantity of opaque gases which are regularly expelled from some of the many volcanoes present on the planet. While the presence of such a layer on an earth-like planet would block sunlight and decrease temperatures dramatically, in the case of Zar'siel I, it is actually a saving grace as it helps reduce the searing rays of its twin stars and prevents them from turning the entire planet into a torched desert.

By contrast, Zar'siel I displays a density almost twice that of Terra despite being smaller, which indicates a very large portion of its mass is taken up by a massive iron core, with much of its crust being fertile in ores of various types.

Climate & Topography
Zar'siel I's very small axial tilt results in a very large temperate band with only small tropical and arctic regions. The region along the equator sees enough sunlight that it is little more than a scorched wasteland while the polar region is, ironically, relatively temperate. The large surface area in-between those two is composed of a variety of semi-arid biomes, primarily steppes and savannas, ranging from pure shrubby grasslands to relatively dense forests. Its seasons are mild due to the faint tilt, although the lack of heat retention contributes to make its winters colder, and its extremely slow revolution make these changes very slow, progressive and long-winded.

Zar'siel I has a fairly small hydrosphere, and while bodies of water present, they represent a relatively small portion of the total surface area, resulting in few precipitations planetwide, less convection of the air, and a need to rely on subterranean sources to survive. Tectonic activity is very high, and there is seldom a time where there isn't an eruption somewhere on the planet. As a result of this activity, the vast steppes and grasslands are criss-crossed by countless chains of mountains, which also results in creating a number of isolated micro-climates.

Biosphere
Zar'siel I is an highly arid world with little water, but unlike many hot worlds of similar properties, it is not a giant wasteland. While its equatorial region is scorched and no life grows there, much of its surface is covered by a sub-arid ecosystem which is gradient, with regions closer to the equator being the most sparse and desolate, and those closer to the poles seeing the most vegetation and lifeforms. Ironically, the high content in CO2 of the atmosphere caused by the volcanic activities spurs the growth of plants and helps them grow. At the same time, this same CO2 content makes the air of variable quality, and the air in wastelands is too think in carbon to be breathed, while that in the most forest areas near the poles are more pure.

The fauna reflects the flora. In regions closer to the equator, only small critters thrive such as arachnids, insectoids and very small mammals or reptiles. The further away from the equator one moves, the larger creatures can be sustained and the more diverse the ecosystem becomes. In large parts, most of the surface is dominated by a variety of mammals and insects. Life also exists within the planet's limit sources of water, but it is also small. Finally, some subterranean ecosystems also exist which have yet to be properly explored and which promise to hold many surprises.

Satellite
The atmosphere and tilt of Zar'Siel I is regulated by a fairly small but extra-dense moon of even higher scale than the planet itself. It has a very thin atmosphere that is just barely breathable, but no life has been observed as its surface is completely scorched by the twin white stars. It is theorized that subterranean ecosystems could also exist there if water is also found beneath the surface, but it is the insane density of the satellite which puzzles the T'au scientists, as the makeup of its core is simply unknown, and the crust is teeming with radioactive materials, resulting in quite the complex enigma.