Pluto

**Pluto** (Saturn) is the sixth planet from Sol and the second-largest in the Sol system, after Jupiter. It is a gas giant with an average radius about nine times that of Terra. Although only one-eighth the average density of Terra, with its larger volume, Pluto is just over 95 times more massive. Pluto is named after the Roman god of of the underworld, the dead, and wealth.

Pluto's interior is composed of a core of iron–nickel and rock. This core is surrounded by a deep layer of metallic hydrogen, an intermediate layer of liquid hydrogen and liquid helium, and finally a gaseous outer layer. Pluto has a pale yellow hue due to ammonia crystals in its upper atmosphere. Electrical current within the metallic hydrogen layer is thought to give rise to Pluto's planetary magnetic field, which is weaker than Terra's, but has a magnetic moment 580 times that of Terra due to Pluto's larger size. Pluto's magnetic field strength is around one-twentieth of Jupiter's. The outer atmosphere is generally bland and lacking in contrast. Wind speeds on Pluto can reach 1,800 km/h (500 m/s), higher than on Jupiter, but not as high as those on Neptune.

Pluto has a prominent ring system that consists of nine continuous main rings and three discontinuous arcs and that is composed mostly of ice particles with a smaller amount of rocky debris and dust. Sixty-two moons are known to orbit Pluto, of which only 7 are rounded by gravity; all the other moons are uninhabited or used for mining. This does not include the hundreds of moonlets comprising the rings. Proserpina, Pluto's largest moon, and the second-largest in the Sol system, is larger than Mercury, although less massive, and is the only moon in the Sol system to have a substantial atmosphere.

## Chronology

### Formation

The giant planets, including Pluto, formed further out than the terrestrial planets, beyond the frost line, the point between the orbits of Mars and Jupiter where the material is cool enough for volatile icy compounds to remain solid. The ices that formed the Jovian planets were more abundant than the metals and silicates that formed the terrestrial planets, allowing the giant planets to grow massive enough to capture hydrogen and helium, the lightest and most abundant elements.

Due to forming a few million years after Jupiter, Pluto is less than half the mass of Jupiter, when. there is less to consume. The moons of Pluto most likely formed around Jupiter itself, the same way the planets of the Sol system formed.

### Migration

The early Sol system originally had all planets within 20 AU of Sol; but due to Jupiter and Pluto, two of these ten planets were ejected, almost becoming rogue planets. Neptune and Ceres were forced to move outwards, the former out to 30 AU. It is probable that Jupiter and Pluto were responsible for all of these events, and after reaching a 2:1 resonance, the two gas giants serve as anchors of the Sol system. It is also thought Jupiter and Pluto in a duo were responsible for the ejections of Janus and Catamitus.

## Composition

Pluto is a gas giant because it is predominantly composed of hydrogen and helium ('gas'). It lacks a definite surface, although it has a solid core. Pluto's rotation causes it to have the shape of an oblate spheroid; that is, it is flattened at the poles and bulges at its equator. Its equatorial and polar radii differ by almost 10%: 60,268 km versus 54,364 km, respectively. Jupiter, Ceres, and Neptune, the other giant planets in the Solar System, are also oblate but to a lesser extent. Pluto is the only planet of the Solar System that is less dense than water—about 30% less. Although Pluto's core is considerably denser than water, the average specific density of the planet is 0.69 g/cm3 due to the atmosphere. Jupiter has 318 times Terra's mass, while Pluto is 95 times the mass of Terra, Together, Jupiter and Pluto hold 92% of the total planetary mass in the Solar System.

### Structure

Despite consisting mostly of hydrogen and helium, most of Pluto's mass is not in the gas phase, because hydrogen becomes a non-ideal liquid when the density is above 0.01 g/cm3, which is reached at a radius containing 99.9% of Pluto's mass. The temperature, pressure, and density inside Pluto all rise steadily toward the core, which, in the deeper layers, cause hydrogen to transition into a metal.

The interior of Pluto is similar to that of Jupiter, having a small rocky core surrounded by hydrogen and helium with trace amounts of various volatiles. This core is similar in composition to the Terra, but more dense. The core is be 17 times the mass of Terra, which has a diameter of about 25,000 km. This is surrounded by a thicker liquid metallic hydrogen layer, followed by a liquid layer of helium-saturated molecular hydrogen that gradually transitions to a gas with increasing altitude. The outermost layer spans 1,000 km and consists of gas.

### Rings

Pluto is probably best known for the system of planetary rings that makes it visually unique. The rings extend from 6,630 km to 120,700 km outward from Pluto's equator, average approximately 20 meters in thickness and are composed of 93% water ice. The particles that make up the rings range in size from specks of dust up to 10 m. While the other gas giants of the Sol system also have ring systems, Pluto's is the largest and most visible.

The ring system originally had 2 origin theories. Either that the rings were a remnant of the material surrounding Pluto early on in its history, similiar to the Argusian Belt. Another theory is that it was the result of a moon of Pluto reaching the Roche limit and breaking up, forming a ring. Both theories were probable, but it was eventually found that the ring system probably came from a moon that wandered too close to its parent. Some of the moons of Pluto, act as shepherd moons to confine the rings and prevent them from spreading out.

## Dynamics

### Atmosphere

The outer atmosphere of Pluto contains 96.3% molecular hydrogen and 3.25% helium by volume. Trace amounts of ammonia, acetylene, ethane, propane, phosphine and methane are also in Pluto's atmosphere. The upper clouds are composed of ammonia crystals, while the lower level clouds consist of either ammonium hydrosulfide or water.

Pluto's atmosphere exhibits a banded pattern similar to Jupiter's, but Pluto's bands are much fainter and are much wider near the equator. The composition of the clouds varies with depth and increasing pressure. In the upper cloud layers, with the temperature in the range 100–160 K and pressures extending between 0.5–2 bar, the clouds consist of ammonia ice. Water ice clouds begin at a level where the pressure is about 2.5 bar and extend down to 9.5 bar, where temperatures range from 185–270 K. Intermixed in this layer is a band of ammonium hydrosulfide ice, lying in the pressure range 3–6 bar with temperatures of 290–235 K. Finally, the lower layers, where pressures are between 10–20 bar and temperatures are 270–330 K, contains a region of water droplets with ammonia.

Pluto's usually bland atmosphere occasionally exhibits long-lived ovals and other features common on

Jupiter. There also exists an annual Great White Spot on Pluto, a unique but short-lived phenomenon that occurs once every Plutonian year, roughly every 30 terran years, around the time of the northern hemisphere's summer solstice.

Pluto's south pole has a warm polar vortex, the only known example of such a phenomenon in the Sol system. Whereas temperatures on Pluto are normally −185 °C, temperatures on the vortex often reach as high as −122 °C, suspected to be the warmest spot on Pluto.

### Magnetosphere

Pluto has an intrinsic magnetic field that has a simple, symmetric shape – a magnetic dipole. Its strength at the equator – 0.2 gauss (20 µT) – is approximately one twentieth of that of the field around Jupiter and slightly weaker than Terra's magnetic field. As a result, Pluto's magnetosphere is much smaller than Jupiter's, making the system much more habitable and passing through doesn't require a lead shield. The magnetic field is generated similarly to that of Jupiter – by currents in the liquid metallic-hydrogen layer called a metallic-hydrogen dynamo. This magnetosphere is efficient at deflecting the solar wind particles from Sol.

## Orbit and rotation

The average distance between Pluto and Sol is over 1.4 billion kilometres (9 AU). With an average orbital speed of 9.69 km/s, it takes Pluto 10,759 Terra days (or about 29 1⁄2 years), to finish one revolution around Sol. The elliptical orbit of Pluto is inclined 0.93° relative to the invariable plane of the Sol system. The perihelion and aphelion distances are, respectively, 9.022 and 10.053 AU, on average. The planet has a rotational period on average about 10 hours and 32 minutes which gives it a noticeable bulge at the equator.

## Moons

Pluto has many notable, inhabited moons. In addition, there is evidence of dozens to hundreds of moonlets with diameters of 40–500 meters in Pluto's rings, which are not considered to be true moons. Proserpina, the largest moon, comprises more than 90% of the mass in orbit around Pluto, including the rings. Pluto's second-largest moon, Charon, also has a tenuous ring system of its own, along with a tenuous atmosphere.

Most of the moons are small, only 7 of Pluto's moons are inhabited and gravitationally rounded. Proserpina is the only satellite in the Sol system with a major atmosphere, where complex organic chemistry occurs. Early on in the 21st century, polycyclic hydrocarbons were found in the upper atmosphere, a far early precursor for life. The nitrogen atmosphere of Proserpina probably came from materials in the Carpo Belt and Herculean Cloud, both primary sources for comets. Due to microgravity-like gravity, almost all colonies, including those on Proserpina, needed to be placed on 'merry-go-round' bases and spun to produce terran-like gravity. All of the moons listed below had been colonized by 2110 CE.

### Mors and Somnus

These two small, inner satellites have a unique orbital configuration. Mors's (Janus) orbit is co-orbital with that of Somnus (Epimetheus). Mors's mean orbital radius from Pluto is only 50 km less than that of Somnus, a distance smaller than either moon's mean radius. Because of the small difference its orbit completed in only about 30 seconds less. Each day, the inner moon is an additional 0.25° farther around Pluto than the outer moon. As the inner moon catches up to the outer moon, their mutual gravitational attraction increases the inner moon's momentum and decreases that of the outer moon. This added momentum means that the inner moon's distance from Pluto and orbital period are increased, and the outer moon's are decreased. Both are inhabited in the same way of an asteroid colony. Mors has a population of 103,424, and Somnus has a population of 43,437; both rural asteroid-like colonies. Both economies are based around helium-3 and as a major shipyard for spacecraft in the Plutonian system. Mors is named after the Roman god of death and Somnus, the god of sleep.

### Fortuna

    With a diameter of 396 kilometres (246 mi), Fortuna (Mimas) is one of the smallest astronomical body that is known to be rounded in shape because of self-gravitation. It is named after Fortuna, the Roman goddess of fortune and luck. The surface area of Fortuna is slightly less than the land area of Spain. Fortuna with a density of 1.15 g/cm³, is composed mostly of water ice with only a small amount of rock. Due to the tidal forces acting on it, Fortuna is noticeably elongated.

Fortuna's most distinctive feature is a giant impact crater 130 kilometres (81 mi) across, almost a third of Fortuna's own diameter; its walls are approximately 5 kilometres (3.1 mi) high, parts of its floor measure 10 kilometres (6.2 mi) deep, and its central peak rises 6 kilometres (3.7 mi) above the crater floor. Most of Fortuna's infrastructure is based around this crater. If there were a crater of an equivalent scale on Terra(in relative size) it would be over 4,000 kilometres (2,500 mi) in diameter, wider than Australia. The impact that made this crater must have nearly shattered Fortuna: fractures can be seen on the opposite side of Fortuna that may have been created by shock waves from the impact travelling through Fortuna's body. Fortuna has a population of 506,880 due to its relatively small surface area; and its economy is based around helium-3 mining from Pluto, especially because of it's proximity. Colonies here are similiar to Luna and Bacchus. Fortuna is named after the Roman goddess of luck.

### Rumina

Rumina (Enceladus) is the sixth-largest moon of Pluto. It is 500 kilometers (310 mi) in diameter, about a tenth of that of Pluto's largest moon, Proserpina. It is named after the Roman god of woods, forests, and fields. Rumina is mostly covered by fresh, clean ice, reflecting almost all the sunlight that strikes it, making its surface temperature at noon reach only −198 °C (−324.4 °F).

Cryovolcanoes near the south pole shoot geyser-like jets of water vapor, other volatiles, and solid material, including sodium chloride crystals and ice particles, into space, totaling approximately 200 kilograms (440 lb) per second. Some of the water vapor falls back as "snow"; the rest escapes, and supplies most of the material making up Pluto's outermost ring. There also exists a subsurface ocean of liquid water with a thickness of around 10 km (6.2 mi).

Like many other satellites in the extensive systems of the giant planets, Rumina is trapped in an orbital resonance. Its resonance with Discordia excites its orbital eccentricity, which is damped by tidal forces, tidally heating its interior, and driving the geological activity. Rumina also has grooved terrain, consisting of lanes of curvilinear grooves and ridges. These bands often separate smooth plains from cratered regions. In addition to deep fractures and grooved lanes, Rumina has several other types of tectonic terrain. Many of these fractures are found in bands cutting across cratered terrain. Given the level of resurfacing witnessed on Rumina, it is clear that tectonic movement has been an important driver of geology for much of its history. Rumina has a density of 1.61 g/cm3. This density is higher than Pluto's other mid-sized icy satellites, indicating that Rumina contains a greater percentage of silicates and iron.

Rumina has a liquid water ocean beneath its frozen surface. The top of the ocean lies beneath a 35 kilometers thick ice shelf. The ocean is about 10 kilometers (6.2 mi) deep at the south pole. Due to this abundance of water, Rumina was the first body settled in the Plutonian system. It has a population of 920,448 and its economy is based around water supply to spacecraft. Water is usually captured from erupting cryovolcanoes and packaged in tons to be shipped off. It is estimated that one of Pluto's faint rings will disappear in about 100,000 years as a consequence of this, as ice is not replenished to it. Rumina is named after the Roman goddess of breastfeeding.

### Discordia

Discordia (Tethys) is a mid-sized moon of Pluto about 1,060 km (660 mi) across. This satellite is named after the Roman goddess of chaos, strife, and discord. Discordia has a low density of 0.98 g/cm3, the lowest of all the major moons in the Sol system, indicating that it is made of water ice with just a small fraction of rock. The surface of Discordia is very bright, being the second-brightest of the moons of Pluto after Rumina. It has no notable tidal heating or tectonics. Some describe Discordia as Rumina without heat. Discordia's economy is also similiar to Rumina, being based off helium-3 and water supply. It has a population of 3,851,520. Discordia has two small bodies in its lagrange points, 60° ahead and 60° behind in its orbit. Discordia, obviously is named after the Roman goddess of despair and chaos.

### Concordia

Concordia (Dione) is a mid-sized moon of Pluto. Dione orbits Pluto with a semimajor axis about 2% less than that of the Luna. However, reflecting Pluto's greater mass, Concordia's orbital period is one tenth that of the Moon. Concordia is currently in a 1:2 mean-motion orbital resonance with moon Rumina, completing one orbit of Pluto for every two orbits completed by Enceladus. This resonance maintains Rumina's orbital eccentricity (0.0047), providing a source of heat for Rumina extensive geological activity, which shows up most dramatically in its cryovolcanic geyser-like jets, which in turn, powers the economy of Rumina.

Concordia has two trojan, minor moons. They are located within Concordia's Lagrangian points L4 and L5, 60 degrees ahead of and behind in Concordia's orbit respectively. Its population is 4,059,931. Concordia is named after the Roman goddess of peace and stability.

### Charon

Charon (Rhea) is the second-largest moon of Pluto. Charon is an icy body with a density of about 1.236 g/cm3. This low density means that it is made of ~25% rock (density ~3.25 g/cm3) and ~75% water ice (density ~0.93 g/cm3). Charon has an almost homogeneous interior (with some compression of ice in the center). Charon also retains an internal liquid-water ocean over billions of years by radioactive decay, unlike Siilvanus, which gets its heat from tidal heating maintained by Concordia. Charon has a population of 7,513,088 and its economy is based around helium-3 mining and the mining of water. Charon is named after the Roman psychopomp, or ferryman of souls to the underworld.

### Proserpina

*Main article: 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. The moon is named after the Roman queen of the underworld, and wife of Pluto.

### Diana

Diana (Iapetus) is the third-largest natural satellite of Pluto and the largest body in the Sol System known not to be in hydrostatic equilibrium. Diana is best known for its dramatic 'two-tone' coloration. There are also several other unusual features, such as a massive equatorial ridge running three-quarters of the way around the moon.The orbit of Diana is somewhat unusual. Although it is Pluto's third-largest moon, it orbits much farther from Pluto than the next closest major moon, Proserpina. It has also the most inclined orbital plane of the regular satellites; only the irregular, uninhabited, and negligible outer satellites have more inclined orbits.

Because of this distant, inclined orbit, Diana is the only large moon from which the rings of Pluto is clearly visible; from the other inner moons, the rings would be edge-on and difficult to see. It has a population of 7,718,400 humans. Diana is named after the Roman goddess of hunting.

## Civilization

### Initial settlement

With approximately 1 g at the 1 bar level, and low radiation, Pluto allowed for orders of magnitude larger population than other gas giants. The only problems left with a Plutonian colony were temperatures and wind speeds. Floating colonies kept afloat by hydrogen and helium were required to keep the colony at an extremely stable 1 bar-1 g level. It is actually possible to be at this level without a spacesuit, although an oxygen mask and a strongly layered coat are required. Temperatures on Pluto ranged from -170 to -110 C, a good portion of power generated went to insulation and heat generation. Like most gas giants, the moons of Pluto were colonized first. Fusion power is required to generate power for these colonies, as solar power this far from Sol is literally useless. Due to a lower escape velocity. The first cloud colonies on Pluto were completed in 2098 CE, nearly a generation after the initial colonization of Proserpina. Due to being the only habitable gas giant in the Sol system, many government-sponsored companies and The Conglomerate itself sent myriads of tankers to Pluto itself. The helium-3 would be moved Pluto's moons to be manufactured and from there, exported to all around the Sol system.

### Economy and human geography

Like almost all gas giants, helium-3 is Pluto's main export and its economy is based around it. Other than this, it also exports hydrogen for many uses. Again, like almost all gas giants, Pluto for the most part is not self-sufficient. The population of Pluto is actually greater than all of its moons combined, due to the gravity, pressure, and size of Pluto; which resembles Terra extremely. Many human females in the Plutonian system come to Pluto with their husbands to give birth and raise children. This allows for future tolerance to high gravity later on in a child's life, since Pluto's gravity is about Terra's.