Selen (Celestial Body)

~ 1% water vapor (climate variable)

0.9340% argon

0.0408% carbon dioxide

0.00182% neon

0.00052% helium

0.00017% methane

0.00006% hydrogen

Selen orbits the gas giant Terhune which is the 5th planet from the sun and the second-largest planet in the Solar System after Vandaran.

Selen is a terrestrial planet with a rich, life sustaining Nitrogen-Oxygen atmosphere, having surface features that are diverse, ranging from grasslands, valleys, deserts, and polar ice caps.

Selen orbits Terhune once every ten days, with the whole system completing a revelation of the sun every 330.328 Selenian days.

Due to the nature of this system, full and partial eclipses are very common on Selen. Both Terhune and Selune are clearly visable to the naked eye on most days.

## Physical characteristics

The shape of Selen is nearly spherical. There is a small flattening at the poles and bulging around the equator due to the planet's rotation. To second order, the Selen is approximately an oblate spheroid, whose equatorial diameter is 41 kilometres larger than the pole-to-pole diameter, although the variation is less than 1% of the average radius of the Selen.

Selen's interior, like that of the other terrestrial planets, is divided into layers by their chemical or physical (rheological) properties. The outer layer is a chemically distinct silicate solid crust, which is underlain by a highly viscous solid mantle. The crust is separated from the mantle by the Mohorovičić discontinuity. The thickness of the crust varies from about 6 kilometres (3.7 mi) under the oceans to 30–50 km (19–31 mi) for the continents. The crust and the cold, rigid, top of the upper mantle are collectively known as the lithosphere, and it is of the lithosphere that the tectonic plates are composed. Beneath the lithosphere is the asthenosphere, a relatively low-viscosity layer on which the lithosphere rides. Important changes in crystal structure within the mantle occur at 410 and 660 km (250 and 410 mi) below the surface, spanning a transition zone that separates the upper and lower mantle. Beneath the mantle, an extremely low viscosity liquid outer core lies above a solid inner core. The Earth's inner core might rotate at a slightly higher angular velocity than the remainder of the planet, advancing by 0.1–0.5° per year. The radius of the inner core is about one fifth of that of Selen.

## Techtonic plates

Selen's mechanically rigid outer layer, the lithosphere, is divided into tectonic plates. These plates are rigid segments that move relative to each other at one of three boundaries types: At convergent boundaries, two plates come together; at divergent boundaries, two plates are pulled apart; and at transform boundaries, two plates slide past one another laterally. Along these plate boundaries, earthquakes, volcanic activity, mountain-building, and oceanic trench formation can occur.

One of these techtonic plates resides underneath Izorah, often reffered to as the 'Greater Izoreen Plate'

## Selune

Selune is a medium sized, terrestial, planet-like natural satellite. It is not known whether the this object is named after the godess Selune or vice versa.

The gravitational attraction between Selen and the Selune causes tides on Selen.