Frigis

(This moon is in the same universe as Cauldron, Cryolith, Phobis Terra, and Behemoth, but is not something I'd plan to make a main part of the actual mod, if it ever gets made.  This description is more for my own enjoyment, and hopefully yours.)

General Description

Frigis is the largest moon of Behemoth, made of about half ice, half rock, and is the farthest out of its three large moons.  It is inactive, although in the past had more activity.  The remnants of this activity includes a weak atmosphere, that is gradually getting worn away by Behemoth's magnetic field plasma.

Surface

The surface of Frigis is covered by a mixture of terrain types, mostly craters, ridges, plains, and small hill regions.  The craters form by impacts, while other other types are eroded remains of past internal activity.  The moon also has great color variation on different regions, going from icy white, to various reddish browns in parts, to large dark areas, formed by different surface ices and organics.

Crater plains, a mixture of flat terrain and large craters, are the most common type of terrain on the moon.  Most areas are partly enclosed by boundary regions of hill and ridge terrain, suggesting interior areas of an old tectonic system.  The craters themselves are in various states of erosion due to the thin atmosphere, and evaporation of ice deposits, with these processes supplying dust to be blown around by the atmosphere.  Smaller craters have either been eroded completely, or filled in by dust.

Ridge regions were previously either contracting or expanding areas in the ancient tectonic system.  Most surviving ridges are highly eroded, with some transitioning into hill belts.  The ridges themselves often appear striped from above, with alternating white and dark areas depending on slope.  Rock slides occur occasionally as well, due to various types of erosion.

Hills come in two general formations, some in belts that often blend into ridge belts, others in clumps within plains.  Both types of hills come from eroded remains of previous formations, the clumps from craters, and the belts from ridges or other tectonic features.  Hills may be colored a number of different ways, but darker areas iun general are more eroded than lighter areas.

Erosion on Frigis takes place largely in two ways: wind, and ice evaporation.  Though the atmosphere is thin, it generates strong winds the move dust, and sometimes etches the surface.  Ice evaporation occurs due to light absorption.  When exposed to light, water and carbon dioxide ice at the surface evaporates, leaving behind organic and dust deposits.

A combination of these two processes often leaves stripe like features on hills and ridges.  Where wind deposits dust, more light is absorbed, evaporating ice.  This evaporation leaves the surface darker, causing more evaporation.  Areas with less wind stay lighter and cooler, and more ice deposits, further lightening the area continuing the cycle.  This process results in light and dark zebra stripes on ridges, and hill clusters that are all white facing one direction, and dark facing another.   On plains, similar processes may occur, but the difference is much less pronounced, due to a much smaller difference in dust erosion and deposition, and to the ease that wind can move ice or dust from one region to another, canceling out the color differences.

Atmosphere

The atmosphere of Frigis is extremely thin, about 1,000 times less dense than Earth's, on average.  It is mostly made of nitrogen and carbon compounds, and is a remnant of gases released during a more active period.

Though thin, the atmosphere transports dust around the surface of Frigis, smoothing plains regions and contributing to color differences between light and dark areas.  Winds also assist in evaporating ice and erosion, but blown dust and evaporated material away.

Clouds, though rare, do occur occasionally on this moon.  When they do firm, clouds resemble a thin ice fog near the surface, composed of water ice or carbon dioxide ice particles.  Dust clouds also occasionally appear, usually when unusually strong winds or vortexes form that can concentrate the dust.

The outer atmosphere is being swept away by Behemoth's magnetospheric plasma.  contributing a small amount of material to Behemoth's magnetic field.  This process will eventually remove all of Frigis's atmosphere.


Explanation

(Disclaimer:  I am not a geologist, planetary scientist, or any other similar sort of scientist, just someone who finds planetary science interesting.  As a result, a lot of these ideas may be impossible, or at least unrealistic.  This probably applies more to these moons than it does to the previous four planets I've written about.  Any mental anguish, property damage, or other negative consequences from reading this blog post are the responsibility of the reader.)

This moon is meant to combine features of Ganymede, Callisto, some other inactive icy moons, and features of Mars's atmosphere.  The old tectonics are based off of ganymede, while the ice evaporation process is largely based off Callisto.  The Atmosphere is mostly Mars based, and added again to make the moon more interesting.