Proserpina

Proserpina (Titan) is the largest moon of Pluto. It is the only natural satellite to have a dense atmosphere in the Sol system. It is the sixth ellipsoidal moon from Pluto. Frequently described as a planet-like moon, Proserpina's diameter is 50% larger than Terra's natural satellite, Luna, and it is 80% more massive. It is the second-largest moon in the Solar System, after Jupiter's moon Juno, and is larger than the smallest planet, Mercury, although only 40% as massive.

Proserpina is primarily composed of water ice and rocky material. The geologically young surface is generally smooth, with few impact craters, with mountains and cryovolcanoes.

The atmosphere of Proserpina is largely nitrogen; minor components lead to the formation of methane–ethane clouds and nitrogen-rich organic smog. The climate—including wind and rain—creates surface features similar to those of Terra, such as dunes, rivers, lakes, seas (of liquid methane–ethane), and deltas, and is dominated by seasonal weather patterns as on Terra. With its liquids (both surface and subsurface) and robust nitrogen atmosphere, Proserpina's methane cycle is analogous to Terra's water cycle, although at a much lower temperature. It has a population of 112,880,000. Due to the low gravity, many colonies are placed in insulated, rotating domes which provide terran-like gravity and allows the colony to retain heat.

## Composition

### Surface

The surface of Proserpina is fluid-processed and geologically young. Proserpina has been around since the Sol System's formation, but its surface is much younger, between 100 million and 150 million years old. Geological processes have reshaped Proserpina's surface.

There are lakes of hydrocarbon on Proserpina, the only satellite in the Sol system to have liquid water on it's surface and the first stable bodies of surface liquid found outside of Terra (by humans).

Channels in some regions have created surprisingly little erosion, suggesting erosion on Proserpina is extremely slow. Overall, these lakes cover only a few percent of the surface, making Proserpina much drier than Terra. Although most of the lakes are concentrated near the poles (where the relative lack of sunlight prevents evaporation), a number of long-standing hydrocarbon lakes in the equatorial desert regions have also been discovered.

Proserpina has hundreds of times more liquid hydrocarbons than all the known oil and natural gas reserves on Terra, and has more organic reserves than all of Terra combined.

#### Conditions

Proserpina's surface temperature is about 94 K (−179.2 °C). At this temperature, water ice has an extremely low vapor pressure, so the little water vapor present is limited to the stratosphere. Proserpina receives about 1% as much sunlight as Terra.

Atmospheric methane creates a greenhouse effect on Proserpina's surface, without which Proserpina would be far colder. Conversely, haze in Proserpina's atmosphere contributes to an anti-greenhouse effect by reflecting sunlight back into space, cancelling a portion of the greenhouse effect and making its surface significantly colder than its upper atmosphere.

### Structure

Proserpina is 5,151 kilometres (3,201 mi) in diameter, compared to 4,879 kilometres (3,032 mi) for the planet Mercury, 3,474 kilometres (2,159 mi) for Luna, and 12,742 kilometres (7,918 mi) for Terra. Proserpina's diameter and mass (and thus its density) are similar to those of the Jovian moons Juno and Bacchus. Based on its bulk density of 1.88 g/cm3, Proserpina's bulk composition is half water ice and half rocky material. Though similar in composition to the inner, major moons of Pluto, it is denser due to gravitational compression.

Proserpina is differentiated into several layers with a 3,400-kilometre (2,100 mi) rocky center surrounded by several layers composed of different crystal forms of ice. Its interior is still hot and there is a liquid layer consisting of a "magma" composed of water and ammonia between the ice Ih crust and deeper ice layers made of high-pressure forms of ice. The presence of ammonia allows water to remain liquid even at a temperature as low as 176 K (−97 °C).

Proserpina's interior is relatively deformable, since Proserpina's surface and crust floats on top of a global ocean. This ocean lies only about 86 kilometers below the surface. This ocean is actually more salty than the dead sea. Methane rainfall interacts with this ocean, which produces ethane and propane with feeds into rivers and lakes.

## Dynamics

### Atmosphere

Proserpina is the only known moon with a significant atmosphere, and its atmosphere is the only nitrogen-rich dense atmosphere in the Solar System aside from Terra's. Proserpina is a "super-rotator", like Venus, with an atmosphere that rotates much faster than its surface. Also, Proserpina's atmosphere is denser than Terra's, with a surface pressure about 1.45 atm. It is also about 1.19 times as massive as Terra's overall, or about 7.3 times more massive on a per surface area basis. It has opaque haze layers that block most visible light from Sol and other sources and renders Proserpina's surface features obscure. Proserpina's lower gravity means that its atmosphere is far more extended than Terra's.

Proserpina's atmospheric composition on average is 96.7% nitrogen with the remaining 3.15% composed mostly of methane. There are trace amounts of other hydrocarbons, such as ethane, diacetylene, methylacetylene, acetylene and propane, and of other gases, such as cyanoacetylene, hydrogen cyanide, carbon dioxide, carbon monoxide, cyanogen, argon and helium. The hydrocarbons are thought to form in Proserpina's upper atmosphere in reactions resulting from the breakup of methane by Sol's ultraviolet light, producing a thick orange smog. Proserpina spends 95% of its time in orbit within Pluto's magnetosphere, which shields it from the solar wind.

## Orbit and rotation

Propserpina orbits Pluto once every 15 days and 22 hours. Like Luna and many of the satellites of the giant planets, its rotational period is identical to its orbital period; Propserpina is thus tidally locked in synchronous rotation with Pluto, and permanently shows one face to the planet. Because of this, there is a sub-Plutonian point on its surface, from which the planet would always appear to hang directly overhead. Its orbital eccentricity is 0.0288, and the orbital plane is inclined 0.348 degrees relative to the Plutonian equator. The small, irregularly shaped satellite of Pluto, Silvanus, is locked in a 3:4 orbital resonance with Propserpina.

## Civilization

### Initial colonies

Pluto and Proserpina are the most important valuable gas giant system in the Sol system. It is much nearer than the ice giants, has virtually no radiation complications, and excellent system of moons; especially because of the resources located in the Plutonian system. Proserpina possesses an abundance of all the elements necessary to support life originating from Terra. In some ways, Proserpina is the most hospitable object in the outer Sol system. The atmosphere contains nitrogen and methane, and in addition, it has liquid methane on its surface replenished by cyrovolcanos. Within colonies, water or oxygen colonies could be added to generate a breathable atmosphere, as air on Terra is mostly nitrogen. Methane could easily be used as fertilizer. The moon has a surface gravity of 0.138 g, slightly less than Luna. This meant that rotating colonies that provided the 1 g that humans need would be built by the first wave of colonists, similiar to Mars.The first wave of colonists had to go through a different process from other colonists. Due to the atmosphere and temperature, special suits with aerogel had to be used. With heat being pumped to the hands, overheating issues were negated. In addition to this, construction of the colony only took about a few weeks, due to the low gravity of Proserpina. Something that weighed 200 pounds on Terra would weigh 27.6 pounds on Proserpina, allowing for fast construction with less need for support. With it's atmosphere and low gravity, flying is possible outside of colonies with strapped-on wings. Along with nuclear power, natural gas is the primary power source of these colonies. The first colonies on Proserpina were established shortly after the start of February 2064 CE. Utilizing discussed concepts the first colonists were able to make the first domed cities within a few months after arriving.

### Economy and human geography

Proserpina, relatively, has a high density for an object in the outer Sol system. With a sustainable population of over 210 million, it rivals Pluto itself in population. Proserpina serves as the primary helium-3 production center in the Sol system, as well as serving as the primary shipyard of the Plutonian system. While Proserpina exports helium-3, it's main focus is the production of carbon nanotubes and exports of fossil fuels, both due to the abundance of hydrocarbons on the surface of Proserpina.