The Solar System is composed of a single G type star, being orbited by 9 major planets and 11 other dwarf planets. It is on the third planet that complex life began to evolve, and where Humanity as a species was born. The Sol system can only be accessed by Commanders once the Sol Permit has been granted to them.

Sol

Sol, or simply "the Sun", is the star at the center of the Solar System. Its spectral classification is G2 V, meaning it is a hot yellow-white star in the main sequence, currently fusing hydrogen into helium in its core. It is a variable star, its brightness fluctuating by 0.1% over the course of 11 years. Sol isn't as active as other stars in its class, which might have helped life to arise and flourish on Earth over billions of years.

Mercury

Mercury is the innermost of the major planets, and the smallest one. It completes one orbit in just under 88 days, and is tidally locked into a 3:2 spin-orbit resonance with Sol, rotating 3 times during every 2 orbits it completes. Its namesake comes from the Roman god Mercurius, messenger of the gods, for this planet moves the faster in the night sky than any other planet does. Since there is no substantial atmosphere here, Mercury experiences wild temperature shifts between its day and night side, the highest reaching 700 K (427 °C), while the lowest can be around 53 K (-220 °C).

Venus

Venus is the second planet in the Solar System, and the hottest one. Its surface is obscured by a thick layer of sulfuric acid clouds, which are highly reflective, making it the brightest planet seen from Earth. This is why it was named after Venus, the Roman goddess of beauty and love. The planet has undergone a runaway greenhouse effect, trapping heat within its carbon dioxide-dominated atmosphere. As a result, despite being farther from the Sun than Mercury is, temperatures around Venus are even hotter than the first planet's, with the average being a staggering 737 K (464 °C), while the atmosphere is much thicker: it has a surface pressure of 92 atm. Venus rotates backwards compared to the other planets, its rotation period being -243 days. This actually makes its rotation period longer than its sidereal orbital period, which is 224 days.

Earth

Earth is the third planet from Sol, and the largest of the terrestrial planets. Life began here around 4 billion years ago, evolving from simple self-replicating cells to complex intelligent life. Life on Earth changed the composition of Earth's atmosphere over time, producing substantial amounts of Oxygen through photosynthesis once cyanobacteria appeared, as well as Ozone. This, in tandem with the planet's strong magnetic field, protects its surface from harmful radiation from Sol and other cosmic sources. The first modern humans came about on the continent of Africa some 300,000 years ago, becoming the dominant species on the planet not long after. Humans further developed their societies through farms and towns to major cities and countries, eventually accomplishing space travel. Humans first set foot on the surface of another celestial body, the Moon, in 1969.

The Moon

The Moon (or less commonly "Luna") is Earth's sole natural satellite. It is theorised to have formed from a major planetary collision between Earth and a Mars-sized body named Theia. This event gave Earth its current axial tilt. Over time, the debris from the impact coalesced into a sphere and began to cool. While during these early times, the Moon had plenty of volcanic activity, this cooling eventually, stopped its volcanism entirely. The vast lunar basalt plains called "seas" (mare) are evidence of this past volcanic activity.
The Moon is tidally locked to Earth, its rotational period being the same as its orbital period. This movement through the sky, visible as different "phases" from the Earth's surface, inspired what are now the months of the year, a month being about the same length as the Moon's orbital period.

The Moon is thought to be a major factor in the development of life, as its gravitational force caused tides on a rapidly-rotating Earth, pulling its liquid oceans back and forth, and thus slowing its rotation. It also stabilizes the planet's axial tilt, making the lengths of the seasons consistent. Some life forms even evolved to recognize and rely on the light of the Moon at night, such as newly hatched sea turtles, which use moonlight to find their way out to the ocean.

Mars

Mars is the fourth planet from Sol, and is the first ever planet to have been successfully terraformed, in 2291. Early in the third millenium, the capital of the Federation has moved from Earth to Mars.
In ancient times, this planet was particularly fascinating to humans because of its visually distinct red color in the sky. This is why it was named after Mars, the Roman god of war.
The planet has a similar axial tilt to Earth at 25.19°. Humans first set foot here in the 2070s, and later on in the 2100s, ancient fossils were uncovered, providing clear evidence that life once existed there. The iron oxide left over from before the terraforming remains on the surface, still giving the planet a red hue from space.

Jupiter

Jupiter is the fifth planet from Sol and the largest in the system. It is a Class I Gas Giant and has more than twice the mass of all the other planets combined. From Earth, it is the third brightest natural object in the night sky, after the Moon and Venus. Its namesake is derived from the Roman god Jupiter, the king of the gods. Out of all the planets, Jupiter is believed to be the oldest, and is composed of 73.7% Hydrogen and 26.3% Helium. It completes a rotation in 9 hours and 55 minutes, and this high rotational speed is what causes the planet's equatorial bulge. The planet's surface cloud layers have an abundance of stripes and storms, but the most notable of which is known as the "Great Red Spot", an enormous storm that has persisted since at least the year 1665.

The Galilean Moons

These 4 moons are known as the Galilean Moons after the astronomer who discovered them in the early 17th century, Galileo Galilei. These natural satellites were the first objects found to be orbiting a body other than the Earth. Their names come from the lovers of the Greek god Zeus, who is the equivalent to Jupiter. These moons are special in their own right: the third moon from Jupiter, Ganymede, is the largest moon in the Solar System, and its diameter greater than that of Mercury, but it's not nearly as massive as the planet. Europa has a subsurface ocean caused by tidal heating between it and Jupiter. Io, Europa and Ganymede are locked in a 4:2:1 orbital resonance.

Galileo's discovery proved that the belief of his time that everything in the sky revolved around the Earth was false: everything revolved around the Sun instead. He also developed a method to determine a person's longitude on Earth based on the predicted timings of eclipses from the moons onto Jupiter. This was actually a precursor to proving that the speed of light is not infinite, but light does in fact take measurable time to travel to its destination.

Saturn

Saturn is the sixth planet from Sol, and the second largest planet in the Sol system. The Class I Gas Giant is famous for its distinctive ring system that has been discernible through even the earliest telescopes. Its namesake is the Roman god of wealth and agriculture. The progenitor for these rings is unknown, but it is thought that these rings are the remains of a moon that was torn apart by the giant's tidal forces. Based on data from Cassini, Saturn's rings are thought to be relatively young on the astronomical scale, having formed possibly within the last 100 million years. However it could also be that the rings are nearly as old as the planet itself, once holding a higher mass of material. Over time as the rings depleted, they evolved to be at the mass we currently measure. Saturn is eventually going to lose its rings in about 100 million years, so they are a temporary feature of the gas giant.

The Moons of Saturn

The Moons of Saturn are fascinating in appearance, as well as in how they interact with one another along their orbits. The most well-known of these moons are Enceladus and Titan. Titan was the first to be discovered by Christian Huygens in 1655, while Tethys, Rhea, Iapetus and Dione were discovered by Giovanni Domenico Cassini, and Enceladus was discovered in 1789 by William Herschel.

Enceladus was the target of many scientific missions since the spacecraft Cassini studied it in close detail in the early 2000s. It is covered in fresh ice, as well as cratered regions, which distinctly separate younger and older regions. Major water vapor ejecta are shot from the moon's south polar regions, with enough velocity to escape the moon's surface gravity. Eventually these gases begin orbiting Saturn itself, forming Saturn's gaseous E ring.

Titan is significant amongst all the moons in the Sol System, as it is the only moon discovered to have a thick atmosphere, not just tenuous gases. It is mostly composed of Nitrogen, with a small percentage of Methane. Titan is also the second largest natural satellite in the Sol System after Ganymede, and it too has a diameter greater than that of Mercury. However, just like the other moon, it is only 40% as massive as the planet. Titan is also the second body ever discovered after the Earth to have stable liquids on its surface, although it's not water: rather, at these cold temperatures (94 K), it is liquid methane instead.

Iapetus has a visually striking surface, with one hemisphere being much brighter than the other. These two hemispheres make its appearance from Earth change in apparent magnitude depending on what side is facing Earth as the moon orbits Saturn. As the moon is tidally locked, the two hemispheres consistently show up in the same places. This led to them being labeled as the bright hemisphere when the moon was to the West, and the dark hemisphere when the moon was to the East of Saturn. The discoverer, Cassini, correctly identified this in the 1700s.

Uranus

Uranus is the seventh planet from Sol, and the largest and least massive of the Ice Giants. Although it is actually visible with the naked eye in sufficiently dark skies, ancient astronomers didn't recognize it as a planet. They thought it was a star, because of its slow orbital velocity meant that the planet didn't travel visibly in the night sky nearly as much as the classical planets did. (After all, the term likely comes from the Greek word planḗtai, which means wanderers, travellers.) The English namesake for this planet and its moons are different than the other planets, as the planet's name Uranus is the Greek god of the sky, whereas the others are named after Roman gods. Uranus was discovered by William Herschel on the 13th of March, 1781. The planet has a significant obliquity, its tilt being 97.7° to its orbit. This means that the planet, as well as the rest of the Uranian moon system, rotate near perpendicularly to its orbital plane. The planet also has a thin ring system, a fact that was discovered on accident when the rings began to occult the star HD 128598, making the star disappear a few times before Uranus did.

Moons of Uranus

The moons of Uranus are named after the queen and king of faeries in medieval and renaissance literature, mostly known from the characters in the works of William Shakespeare and Alexander Pope. Herschel discovered Titania and Oberon six years after the discovery of Uranus, and in 1851, Ariel and Umbriel were discovered by William Lassell. Miranda was found in 1948 by Gerard Kuiper, and the other moons were discovered either by the flyby of Voyager 2, or through other advanced Earth-based telescopes.

Neptune

Neptune is the eighth planet from Sol, and the smallest and most massive of the Ice Giants. The planet's namesake comes from Neptune, the Roman god of the sea. Unlike the planets before it, Neptune is not visible to the naked eye. It was the first planet to be found using mathematical prediction instead of direct observation. The observed orbit of Uranus did not follow its mathematically calculated orbit well enough, which led Alexis Bouvard to hypothesize that there must be another planet beyond Uranus that perturbs it. Urbain Le Verrier calculated where this hypothetical planet might be, and Johann Galle eventually found it within a degree of where Le Verrier predicted it would be. The planet has a very faint ring system, the first of which was discovered in 1968 by Edward Guinan.

Triton

Triton is a peculiar moon in the Sol System, as it orbits Neptune in retrograde, and its orbit is also inclined 129° to the ecliptic - and yet, its eccentricity is only 0.000016. It is thought to be a captured dwarf planet from the nearby Kuiper Belt. It is the seventh largest moon in the Sol System. For reasons unknown, Triton is permit locked by the Pilot's Federation, and no ships are currently allowed to land there.

The Trans-Neptunian Dwarf Planets

The Trans-Neptunian Dwarf Planets are small planetary bodies in the outer reaches of the Solar System, beyond Neptune's orbit. The IAU does not classify these bodies as "regular" planets, as they have not cleared their surrounding neighborhood of matter. They are found mostly in a region beyond the orbit of Neptune, populated by many small icy bodies called the Kuiper Belt.
These bodies might have differentiated interiors. Their masses were originally found by studying the orbital period of the dwarf planet's moon, if one existed. Their diameters were also originally found by studying the occultations of background stars, when the body briefly passes in front of a star.

Pluto and Charon make up a double dwarf planet system in the Kuiper Belt. They were discovered by Clyde W. Tombaugh on February 18, 1930, and Charon was discovered to be a separate body much later, in 1978, by James Christy. At the time of Pluto's discovery, astronomers insisted that Uranus' perturbed orbit could not be explained just by Neptune alone, so they kept searching for the so-called "Planet X". Tombaugh was using a blink comparator to search for small movements in certain night sky pictures when he found Pluto and Charon.

The Pluto-Charon barycentre is in a 2:3 orbital resonance with Neptune. In fact, when viewing the entire solar system from above, Pluto's orbit appears to overtake Neptune's, being closer to the Sun than it. However, Pluto's orbit is inclined as such that its orbital path takes it 8 AU above Neptune's.

Eris is the second largest dwarf planet and the most massive, being heavier than Pluto is. It was discovered in 2005 from images taken two years earlier. Because it is heavier than Pluto, and at first appeared larger than it, after its discovery the IAU at first named it as the tenth planet of the Solar system. However, as more and more such Trans-Neptunian Objects were discovered (their discovered numbers reached into the thousands by the 2020s), after much debate the union adopted a new formal definition of dwarf planets, which meant that Eris was no longer considered the tenth planet.
Eris has an orbital period of 559 days, and is inclined from the ecliptic by 44°. It is the second brightest large body by albedo at 0.96, only being surpassed by Enceladus.

Haumea is the third largest dwarf planet behind Eris and Pluto, and was discovered in 2004. It completes one day in just under four hours, and has transformed into a triaxial ellipsoid as a result. This is expected as the body shows clear color variations as it rotates, a fast rotation period being the only logical explanation.

Orcus is the eighth largest dwarf planet and has one moon, Vanth. Orcus was discovered in 2004, Vanth a year later. The body is in a 2:3 orbit resonance with Neptune, just like Pluto. Orcus has earned the nickname "Anti-Pluto" because of similarities in their orbital periods, inclinations and eccentricities, and it also has a large satellite.

Sedna is a dwarf planet in the outer solar system, one of the most far away we know of. It was discovered in 2003. Its closest approach to Sol only brings it to a distance of 76.2 AU, and its aphelion goes out to around 937 AU, a full orbit taking approximately 11,400 years. Its eccentricity is 0.8496. Sedna's surface is dotted by red regions, tholins caused by the breakdown of carbon compounds by Sol's ultraviolet light.

Salacia was discovered in 2004 and has a single moon, Actaea. The moon orbits Salacia in 5.5 days. The planet has a very low albedo of 0.04, making its surface barely distinguishable from the blackness of space.

Quaoar was discovered in 2002 and takes 288 years to orbit Sol. It completes one full day in 8.8 hours, causing it to form the shape of an oblate spheroid, much like that of Earth.

2002 MS4 is a Kuiper Belt object discovered in 2002. As it is currently passing through a dense star field, multiple stellar occultations were used to determine its diameter, which is 500 miles (800km). It is the largest unnamed object in the system.

2007 OR10 is a Scattered Disc body that completes a full orbit in 554 years, the third longest of all dwarf planets. In 2009 the Minor Planet Center assigned the name Gonggong to this body.

Makemake is a reddish Kuiper Belt object discovered in 2005. It takes 306 years to complete one orbit. Its orbit is inclined to 29°.

Persephone

Persephone is a dark and icy body nearly 10 times the mass of the Earth on a very long orbit around the Sun, taking 20,000 years to complete one orbit. It was first hypothesized to exist from apparent perturbations in the eccentric orbits of very distant Kuiper Belt objects. Throughout its search it was tagged as "Planet Nine". Astronomers correctly predicted that something was shepherding these bodies into peculiar orbits, for example the large perihelion of Sedna. It also explained why objects in near-perpendicular orbits have big semi-major axes. This is the second planet whose existence was discovered by orbital perturbation.

The Solar System is composed of a single G type star, being orbited by eight major planets and numerous other dwarf planets. It is on the third planet that complex life began to evolve, and where Humanity as a species was born. The Sol system can only be accessed by Commanders once the Sol Permit has been granted to them.

Sol

Sol, or simply "the Sun", is the star at the center of the Solar System. Its spectral classification is G2 V, meaning it is a hot yellow-white star in the main sequence, currently fusing hydrogen into helium in its core. It is a variable star, its brightness fluctuating by 0.1% over the course of 11 years. Sol isn't as active as other stars in its class, which might have helped life to arise and flourish on Earth over billions of years.

Mercury

Mercury is the innermost of the major planets, and the smallest one. It completes one orbit in just under 88 days, and is tidally locked into a 3:2 spin-orbit resonance with Sol, rotating 3 times during every 2 orbits it completes. Its namesake comes from the Roman god Mercurius, messenger of the gods, for this planet moves the faster in the night sky than any other planet does. Since there is no substantial atmosphere here, Mercury experiences wild temperature shifts between its day and night side, the highest reaching 700 K (427 °C), while the lowest can be around 53 K (-220 °C).

Venus

Venus is the second planet in the Solar System, and the hottest one. Its surface is obscured by a thick layer of sulfuric acid clouds, which are highly reflective, making it the brightest planet seen from Earth. This is why it was named after Venus, the Roman goddess of beauty and love. The planet has undergone a runaway greenhouse effect, trapping heat within its carbon dioxide-dominated atmosphere. As a result, despite being farther from the Sun than Mercury is, temperatures around Venus are even hotter than the first planet's, with the average being a staggering 737 K (464 °C), while the atmosphere is much thicker: it has a surface pressure of 92 atm. Venus rotates backwards compared to the other planets, its rotation period being -243 days. This actually makes its rotation period longer than its sidereal orbital period, which is 224 days.

Earth

Earth is the third planet from Sol, and the largest of the terrestrial planets. Life began here around 4 billion years ago, evolving from simple self-replicating cells to complex intelligent life. Life on Earth changed the composition of Earth's atmosphere over time, producing substantial amounts of Oxygen through photosynthesis once cyanobacteria appeared, as well as Ozone. This, in tandem with the planet's strong magnetic field, protects its surface from harmful radiation from Sol and other cosmic sources. The first modern humans came about on the continent of Africa some 300,000 years ago, becoming the dominant species on the planet not long after. Humans further developed their societies through farms and towns to major cities and countries, eventually accomplishing space travel. Humans first set foot on the surface of another celestial body, the Moon, in 1969.

The Moon

The Moon (or less commonly "Luna") is Earth's sole natural satellite. It is theorised to have formed from a major planetary collision between Earth and a Mars-sized body named Theia. This event gave Earth its current axial tilt. Over time, the debris from the impact coalesced into a sphere and began to cool. While during these early times, the Moon had plenty of volcanic activity, this cooling eventually, stopped its volcanism entirely. The vast lunar basalt plains called "seas" (mare) are evidence of this past volcanic activity.
The Moon is tidally locked to Earth, its rotational period being the same as its orbital period. This movement through the sky, visible as different "phases" from the Earth's surface, inspired what are now the months of the year, a month being about the same length as the Moon's orbital period.

The Moon is thought to be a major factor in the development of life, as its gravitational force caused tides on a rapidly-rotating Earth, pulling its liquid oceans back and forth, and thus slowing its rotation. It also stabilizes the planet's axial tilt, making the lengths of the seasons consistent. Some life forms even evolved to recognize and rely on the light of the Moon at night, such as newly hatched sea turtles, which use moonlight to find their way out to the ocean.

Mars

Mars is the fourth planet from Sol, and is the first ever planet to have been successfully terraformed, in 2291. Early in the third millenium, the capital of the Federation has moved from Earth to Mars.
In ancient times, this planet was particularly fascinating to humans because of its visually distinct red color in the sky. This is why it was named after Mars, the Roman god of war.
The planet has a similar axial tilt to Earth at 25.19°. Humans first set foot here in the 2070s, and later on in the 2100s, ancient fossils were uncovered, providing clear evidence that life once existed there. The iron oxide left over from before the terraforming remains on the surface, still giving the planet a red hue from space.

Jupiter

Jupiter is the fifth planet from Sol and the largest in the system. It is a Class I Gas Giant and has more than twice the mass of all the other planets combined. From Earth, it is the third brightest natural object in the night sky, after the Moon and Venus. Its namesake is derived from the Roman god Jupiter, the king of the gods. Out of all the planets, Jupiter is believed to be the oldest, and is composed of 73.7% Hydrogen and 26.3% Helium. It completes a rotation in 9 hours and 55 minutes, and this high rotational speed is what causes the planet's equatorial bulge. The planet's surface cloud layers have an abundance of stripes and storms, but the most notable of which is known as the "Great Red Spot", an enormous storm that has persisted since at least the year 1665.

The Galilean Moons

These 4 moons are known as the Galilean Moons after the astronomer who discovered them in the early 17th century, Galileo Galilei. These natural satellites were the first objects found to be orbiting a body other than the Earth. Their names come from the lovers of the Greek god Zeus, who is the equivalent to Jupiter. These moons are special in their own right: the third moon from Jupiter, Ganymede, is the largest moon in the Solar System, and its diameter greater than that of Mercury, but it's not nearly as massive as the planet. Europa has a subsurface ocean caused by tidal heating between it and Jupiter. Io, Europa and Ganymede are locked in a 4:2:1 orbital resonance.

Galileo's discovery proved that the belief of his time that everything in the sky revolved around the Earth was false: everything revolved around the Sun instead. He also developed a method to determine a person's longitude on Earth based on the predicted timings of eclipses from the moons onto Jupiter. This was actually a precursor to proving that the speed of light is not infinite, but light does in fact take measurable time to travel to its destination.

Saturn

Saturn is the sixth planet from Sol, and the second largest planet in the Sol system. The Class I Gas Giant is famous for its distinctive ring system that has been discernible through even the earliest telescopes. Its namesake is the Roman god of wealth and agriculture. The progenitor for these rings is unknown, but it is thought that these rings are the remains of a moon that was torn apart by the giant's tidal forces. Based on data from Cassini, Saturn's rings are thought to be relatively young on the astronomical scale, having formed possibly within the last 100 million years. However it could also be that the rings are nearly as old as the planet itself, once holding a higher mass of material. Over time as the rings depleted, they evolved to be at the mass we currently measure. Saturn is eventually going to lose its rings in about 100 million years, so they are a temporary feature of the gas giant.

The Moons of Saturn

The Moons of Saturn are fascinating in appearance, as well as in how they interact with one another along their orbits. The most well-known of these moons are Enceladus and Titan. Titan was the first to be discovered by Christian Huygens in 1655, while Tethys, Rhea, Iapetus and Dione were discovered by Giovanni Domenico Cassini, and Enceladus was discovered in 1789 by William Herschel.

Enceladus was the target of many scientific missions since the spacecraft Cassini studied it in close detail in the early 2000s. It is covered in fresh ice, as well as cratered regions, which distinctly separate younger and older regions. Major water vapor ejecta are shot from the moon's south polar regions, with enough velocity to escape the moon's surface gravity. Eventually these gases begin orbiting Saturn itself, forming Saturn's gaseous E ring.

Titan is significant amongst all the moons in the Sol System, as it is the only moon discovered to have a thick atmosphere, not just tenuous gases. It is mostly composed of Nitrogen, with a small percentage of Methane. Titan is also the second largest natural satellite in the Sol System after Ganymede, and it too has a diameter greater than that of Mercury. However, just like the other moon, it is only 40% as massive as the planet. Titan is also the second body ever discovered after the Earth to have stable liquids on its surface, although it's not water: rather, at these cold temperatures (94 K), it is liquid methane instead.

Iapetus has a visually striking surface, with one hemisphere being much brighter than the other. These two hemispheres make its appearance from Earth change in apparent magnitude depending on what side is facing Earth as the moon orbits Saturn. As the moon is tidally locked, the two hemispheres consistently show up in the same places. This led to them being labeled as the bright hemisphere when the moon was to the West, and the dark hemisphere when the moon was to the East of Saturn. The discoverer, Cassini, correctly identified this in the 1700s.

Uranus

Uranus is the seventh planet from Sol, and the largest and least massive of the Ice Giants. Although it is actually visible with the naked eye in sufficiently dark skies, ancient astronomers didn't recognize it as a planet. They thought it was a star, because of its slow orbital velocity meant that the planet didn't travel visibly in the night sky nearly as much as the classical planets did. (After all, the term likely comes from the Greek word planḗtai, which means wanderers, travellers.) The English namesake for this planet and its moons are different than the other planets, as the planet's name Uranus is the Greek god of the sky, whereas the others are named after Roman gods. Uranus was discovered by William Herschel on the 13th of March, 1781. The planet has a significant obliquity, its tilt being 97.7° to its orbit. This means that the planet, as well as the rest of the Uranian moon system, rotate near perpendicularly to its orbital plane. The planet also has a thin ring system, a fact that was discovered on accident when the rings began to occult the star HD 128598, making the star disappear a few times before Uranus did.

Moons of Uranus

The moons of Uranus are named after the queen and king of faeries in medieval and renaissance literature, mostly known from the characters in the works of William Shakespeare and Alexander Pope. Herschel discovered Titania and Oberon six years after the discovery of Uranus, and in 1851, Ariel and Umbriel were discovered by William Lassell. Miranda was found in 1948 by Gerard Kuiper, and the other moons were discovered either by the flyby of Voyager 2, or through other advanced Earth-based telescopes.

Neptune

Neptune is the eighth planet from Sol, and the smallest and most massive of the Ice Giants. The planet's namesake comes from Neptune, the Roman god of the sea. Unlike the planets before it, Neptune is not visible to the naked eye. It was the first planet to be found using mathematical prediction instead of direct observation. The observed orbit of Uranus did not follow its mathematically calculated orbit well enough, which led Alexis Bouvard to hypothesize that there must be another planet beyond Uranus that perturbs it. Urbain Le Verrier calculated where this hypothetical planet might be, and Johann Galle eventually found it within a degree of where Le Verrier predicted it would be. The planet has a very faint ring system, the first of which was discovered in 1968 by Edward Guinan.

Triton

Triton is a peculiar moon in the Sol System, as it orbits Neptune in retrograde, and its orbit is also inclined 129° to the ecliptic - and yet, its eccentricity is only 0.000016. It is thought to be a captured dwarf planet from the nearby Kuiper Belt. It is the seventh largest moon in the Sol System. For reasons unknown, Triton is permit locked by the Pilot's Federation, and no ships are currently allowed to land there.

The Trans-Neptunian Dwarf Planets

The Trans-Neptunian Dwarf Planets are small planetary bodies in the outer reaches of the Solar System, beyond Neptune's orbit. The IAU does not classify these bodies as "regular" planets, as they have not cleared their surrounding neighborhood of matter. They are found mostly in a region beyond the orbit of Neptune, populated by many small icy bodies called the Kuiper Belt.
These bodies might have differentiated interiors. Their masses were originally found by studying the orbital period of the dwarf planet's moon, if one existed. Their diameters were also originally found by studying the occultations of background stars, when the body briefly passes in front of a star.

Pluto and Charon make up a double dwarf planet system in the Kuiper Belt. They were discovered by Clyde W. Tombaugh on February 18, 1930, and Charon was discovered to be a separate body much later, in 1978, by James Christy. At the time of Pluto's discovery, astronomers insisted that Uranus' perturbed orbit could not be explained just by Neptune alone, so they kept searching for the so-called "Planet X". Tombaugh was using a blink comparator to search for small movements in certain night sky pictures when he found Pluto and Charon.

The Pluto-Charon barycentre is in a 2:3 orbital resonance with Neptune. In fact, when viewing the entire solar system from above, Pluto's orbit appears to overtake Neptune's, being closer to the Sun than it. However, Pluto's orbit is inclined as such that its orbital path takes it 8 AU above Neptune's.

Eris is the second largest dwarf planet and the most massive, being heavier than Pluto is. It was discovered in 2005 from images taken two years earlier. Because it is heavier than Pluto, and at first appeared larger than it, after its discovery the IAU at first named it as the tenth planet of the Solar system. However, as more and more such Trans-Neptunian Objects were discovered (their discovered numbers reached into the thousands by the 2020s), after much debate the union adopted a new formal definition of dwarf planets, which meant that Eris was no longer considered the tenth planet.
Eris has an orbital period of 559 days, and is inclined from the ecliptic by 44°. It is the second brightest large body by albedo at 0.96, only being surpassed by Enceladus.

Haumea is the third largest dwarf planet behind Eris and Pluto, and was discovered in 2004. It completes one day in just under four hours, and has transformed into a triaxial ellipsoid as a result. This is expected as the body shows clear color variations as it rotates, a fast rotation period being the only logical explanation.

Orcus is the eighth largest dwarf planet and has one moon, Vanth. Orcus was discovered in 2004, Vanth a year later. The body is in a 2:3 orbit resonance with Neptune, just like Pluto. Orcus has earned the nickname "Anti-Pluto" because of similarities in their orbital periods, inclinations and eccentricities, and it also has a large satellite.

Sedna is a dwarf planet in the outer solar system, one of the most far away we know of. It was discovered in 2003. Its closest approach to Sol only brings it to a distance of 76.2 AU, and its aphelion goes out to around 937 AU, a full orbit taking approximately 11,400 years. Its eccentricity is 0.8496. Sedna's surface is dotted by red regions, tholins caused by the breakdown of carbon compounds by Sol's ultraviolet light.

Salacia was discovered in 2004 and has a single moon, Actaea. The moon orbits Salacia in 5.5 days. The planet has a very low albedo of 0.04, making its surface barely distinguishable from the blackness of space.

Quaoar was discovered in 2002 and takes 288 years to orbit Sol. It completes one full day in 8.8 hours, causing it to form the shape of an oblate spheroid, much like that of Earth.

2002 MS4 is a Kuiper Belt object discovered in 2002. As it is currently passing through a dense star field, multiple stellar occultations were used to determine its diameter, which is 500 miles (800km). It is the largest unnamed object in the system.

2007 OR10 is a Scattered Disc body that completes a full orbit in 554 years, the third longest of all dwarf planets. In 2009 the Minor Planet Center assigned the name Gonggong to this body.

Makemake is a reddish Kuiper Belt object discovered in 2005. It takes 306 years to complete one orbit. Its orbit is inclined to 29°.

Persephone

Persephone is a dark and icy body nearly 10 times the mass of the Earth on a very long orbit around the Sun, taking 20,000 years to complete one orbit. It was first hypothesized to exist from apparent perturbations in the eccentric orbits of very distant Kuiper Belt objects. Throughout its search it was tagged as "Planet Nine". Astronomers correctly predicted that something was shepherding these bodies into peculiar orbits, for example the large perihelion of Sedna. It also explained why objects in near-perpendicular orbits have big semi-major axes. This is the second planet whose existence was discovered by orbital perturbation.