Doppel

(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

The second large moon from Behemoth, Doppel is a roughly Ganymede sized moon, made of about 2/5 ice, the rest rock, with rock, water, and metal separated into different layers.  The moon is named for its surprising similarity to Earth like planets, but with different materials.  Energy from tidal heating powers tectonics and volcanoes, a thick atmosphere generates similar types of weather, and surface rivers and lakes forms a similar surface.

Interior

Tidal heating, and radioactive heating, within Doppel create a water layer within the upper ice layer of the moon.   Movement and heating within this water layer drives tectonics at the surface, and occasionally independent water volcanoes.  The surface ice itself varies in thickness, but all crust is roughly tens of miles thick.  At the surface, tectonic motions are visible in large valleys and rift areas, usually filled by organic oceans, as well as mountain belts.  Rifting areas allow water to reach the surface, where lower pressures release gas, driving the water outward.  Isolated volcanoes form in a similar way, as water seeps through weaknesses in ice, and as the lower pressures release gas, the water is further carried upward to the surface.

Surface

Erosion by wind and organics, as well as organic rain, turns much of the surface of Doppel into a paste of mixed organics and ice particles.   A few drier areas contain looser particles, and dunes or desert like features can form in these regions.  This paste becomes harder in colder areas, much like a permafrost, allowing similar features.  The organic material within the paste never form a fixed composition, and temperature changes or leeching can sometimes change the properties of the paste by removing or adding components, sometimes causing mudslides.

Most low altitude areas of the moon are filled with organic liquids, either in small lakes, or in long "oceans", formed over rifts.  The floors of these oceans usually contain "cliffs", dropping from the level of dry terrain to a much lower level on the ocean floor, but slumping ice, and deposits of eroded ice from land usually smooth out these features somewhat.

Mountains,  although not nearly as tall as on Earth, are still rugged and difficult to traverse.  They interact with the atmosphere in a similar way, creating organic rains, and deflecting winds somewhat.  Fewer rivers have their origin in mountains than on Earth like planets, but enough do to give a similar appearance, and erode the mountains.

Isolated  volcanoes are usually visible as small hills or mountains surrounded by a flat landscape.  These structures are usually inactive, only releasing small amounts of gas over time, but occasionally release large amounts of gaseous water. 

Rivers, Seas, lakes, and Rain

Possibly the most unusual feature of Doppel are the large organic lakes, oceans, and rivers found throughout the moon.  The liquid in these features is a mixture of materials, mostly methane and formaldehyde, but with other simple organics such as methanol, ethane, methylamine, carbon dioxide, and such in small amounts as well.  Methane, formaldehyde, and carbon dioxide largely come from ice volcanoes or rifts, while other organic materials are largely formed in the atmosphere from photochemical reactions.

Depending on temperature, liquid areas may have different compositions, and slightly different erosion and flow properties as a result.  Rivers, in particular, may leech material from surrounding paste as their temperature changes, sometimes leading to mudslides, and eroding shores faster than would otherwise occur.  The composition of rain may also change from regions to region, effecting the physical properties of the resulting paste.

Where rivers meet lakes or seas, large deltas form.  Mostly, these are formed of ice particles, but may also contain solid organics or paste if conditions are right.  This material will eventually fill lakes, and in rifts, the structure will often stretch close to the central volcanic zone.  Currents carry this material throughout the sea, coating the floor with a padding of loose particles/

Within lakes and seas, sluggish currents form, supported by winds and, in oceans, by heat from below.  Ocean currents largely flow linearly, along the rifts, as the small width of these features allows less side to side movement.  Deltas also obstruct movement, and the constricted currents often shave off the tip of the delta somewhat.

Atmosphere

The atmosphere or Doppel is formed by gases released from volcanoes, and from reactions of those gases.   It is mostly made of nitrogen, methane, and carbon dioxide, with small amounts of formaldehyde, ammonia, and other trace gases.   It has a density about the same as Earth's atmosphere.

Ice Volcanoes and Rifts on Doppel largely release carbon dioxide, ammonia, formaldehyde, and methane, though other material emerge as well.  Released ammonia either freezes to ice, or escapes to the atmosphere, where it is largely broken down to nitrogen.  Formaldehyde, methane, and carbon dioxide released in seas or lakes usually liquify and join the lake or sea.  When released onto a land surface, they either join the atmosphere or contribute to organic paste on the surface.  in the atmosphere, gas may either condense into clouds, or react photochemically, producing further organics.

Winds in the atmosphere follow a simple pattern, surface winds largely flow to the a warmer pole, upper level winds to a colder pole.  These winds are disrupted by mountains, or by unusually cold or warm areas.

Clouds and Rain on Doppel are largely formed by organic material, whether formed high in the atmosphere, or from evaporated surface material.  Clouds, and the rain formed from them, have different compositions depending on temperature and the source of the air feeding them, resulting sometimes in unusual colors.  Rain as well may change composition as it falls through the air, also sometimes changing color as it falls if the right materials are mixed.  Even without large clouds, organic haze is common in the upper atmosphere, and material slowly falling from this haze feeds some lower level clouds, or creates dust that eventually joins the paste at the surface.

In the upper atmosphere, material is swept into the larger magnetic field of Behemoth, and auroras occur, though these are hard to spot.

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 mostly based on Titan, although a titan with much more volcanic activity than it currently has.  The composition of materials is also different, to stay consistent with Fumarole loosing carbon dioxide, Doppel should likely also release oxygen contain materials in addition to methane.  Otherwise, tectonic features were based somewhat on Europa.

In the atmosphere, I assume that the extra gas release from volcanoes compensates for gas lost to the magnetosphere, although (like most ideas I have for these moons) I'm not sure if the numbers would actually work out.