The Alpha Centauri System (or simply Alpha Centauri) is a trinary star system located in the constellation of Centaurus. This trinary star system consists of a yellow dwarf, Alpha Centauri A, an orange dwarf, Alpha Centauri B, and a red dwarf, Proxima Centauri.
Its distance from Earth is approximately 4.37 light years, making it the closest star system in the galaxy to the Solar System as well as the third brightest star in Earth's night sky.[1]
History[]
In December of 1689, Jean Richaud first discovered Alpha Centauri A along with Alpha Centauri B while observing a comet from his station in Puducherry. He was the first to recognize the two stars’ binary nature. This was not the first binary system discovered, as Acrux was discovered to be a binary system prior to Alpha Centauri.[2]
The three gas giants orbiting Alpha Centauri B were discovered by observatories on Earth. The five terrestrial planets were found two decades later. Since the arrangement of the planets resembled our own Solar System, they were named for their counterparts. The three gas giants in the system orbited far enough from ACB to be perturbed by its companion star, so their orbits were chaotic and varied wildly. Given these perturbations, there was speculation regarding the possibility of a collision between Cronus and Poseidon in the next century. If any satellites had ever formed around these gas giants in the past, they had long ago been ejected or drawn into the planet.
The three gas giants around ACA were not found until after COSTIN went into full operation. Upon their discovery they were named Oceanus, Crius, and Coeus.
Exploration[]
When the first interstellar ship, the ISV Bradbury (5 kilometers long) arrived near Alpha Centauri B, it discovered that the three largest terrestrial planets had environments and atmospheric compositions far removed from their namesakes. There was no sign of any life on these planets:
- Unlike Venus, Aphrodite had almost no atmosphere.
- Gaea had undergone a massive greenhouse effect similar to Earth.
- Ares had an atmosphere of 90% nitrogen and too little carbon dioxide for terraforming.
- Vulcan and Hermes were airless hellscapes, similar to Mercury.
The explorers were deeply disappointed. They had little hope for better results in the Alpha Centauri A system, which they would reach about ten months later.
The two terrestrial planets they had discovered along the way with their onboard telescope had unstable orbits, well outside the habitable zone. However, the Alpha Centauri A system turned out to be full of surprises. As they observed the two terrestrial planets on approach, they found they were mostly ice surrounding a rocky core. Like the gas giants orbiting around Alpha Centauri B, their orbits were chaotic. The crew named them "Odyssey" and "Ulysses".
Next came Coeus, the outermost gas giant. As a gas giant, it was unremarkable with no interesting properties. But its two largest moons; Dionysus and Bacchus, were strange. Dionysus was about 19,000 km (11,806 mi) in diameter, and had a classic orbit around the gas giant. But Bacchus on the other hand, was less than 500 km (311 mi) wide and spun wildly, looping around Coeus and Dionysus in a "flower petal" orbit. The crew named this moon "Bacchus]" because of its "staggering" orbit. The rest of Coeus' moons were just small, atmosphere-less satellites with many of them being asteroids; So, the crew simply ignored them and moved on.
Polyphemus seen in the series
Then came Crius, which sits in ACA's habitable zone. The crew immediately noticed the massive eye-shaped storm, far larger than Jupiter's "Great Red Spot". They renamed the planet "Polyphemus" after the cyclops of the same name from Homer's epic The Odyssey. The new name was officially adopted after the crew returned to Earth eight years later. But the moons were even more astonishing than the giant storm: clouds and oceans were visible on all moons larger than 6,500 km (4,039 mi) in diameter, except three. Remote sensors revealed nitrogen-hydrogen atmospheres, with a few percent carbon dioxide on the fifth and sixth moons. Such an atmosphere could only be produced by a carbon-based life cycle. While some other large satellites also had surface water, their thinner atmospheres were mainly nitrogen and carbon dioxide, preventing life from developing.
More surprises awaited. In fact, the innermost moon, Dante, orbited Polyphemus as close as possible without being torn apart by gravitational pressure. The next moon, Hades, followed an elliptical orbit that regularly brought it close to Dante, causing tidal heating that pushed its temperature above 900 °K (627 °C or 1,161 °F). The heat gave it a faint red glow. Though not experiencing nuclear fusion like Hades, Dante experienced constant moonquakes and had volcanoes in perpetual eruption. The moons orbiting beyond Cassandra were more ordinary, until Chaos, a fractured moon, similar to Miranda, with a rugged surface, and cliffs going as high as 15 to 30 km (9.32 to 18.64 mi).
Location[]
The astronomical coordinates for the Centaurus star system are right ascension 14 h 39.6 m; declination -60 degrees 50'. Alpha Centauri A and B are located approximately 4.37 light years or 277,600 astronomical units (AU) from Earth (1 AU is the average distance of Earth from the Sun, about 93,000,000 miles). Alpha Centauri C (also called "Proxima Centauri" because it is the closest of the three stars to Earth) is about 0.13 light-years closer.
Orbital Elements[]
Alpha Centauri A and B have a highly elliptical orbit (e = 0.52) about their common center of mass, with their separation ranging from 11.2 to 35.6 AU; it takes slightly less than eighty years for them to complete one revolution. Recent periastrons (point of closest approach) were in 1955, 2035, 2115, and the next one will occur in 2195. Alpha Centauri C, located more than 10,000 AU away from ACA and ACB, is very weakly bound to them by gravity and takes approximately a million years to orbit the two larger stars. It is possible that perturbations by the next closer stars may eventually disrupt ACC's orbit, and free it to wander by itself.
Stars[]
Alpha Centauri A is orbited by 5 planets.
Alpha Centauri is a trinary star system, meaning that it has three stars. It is Earth's closest stellar neighbor outside the Solar System.
- Alpha Centauri A (ACA) (Na'vi name: Tsawke meaning "sun") is the largest member of the system and about 20% larger than Earth's sun, but otherwise very similar. ACA would be otherwise unremarkable were it not for the fact that it serves as the sun for Pandora, a large moon that orbits the gas giant Polyphemus. It was on Pandora that explorers encountered the Na'vi, the only intelligent species yet discovered in outer space. Pandora is also the only known source for unobtanium, a high temperature superconductor essential for many of Earth's technologies.
- Alpha Centauri B (ACB) (Na'vi name: Tsawkenay meaning "lesser sun") is about 15% smaller than Earth's sun, and noticeably orange because it is 500 Kelvin cooler than its neighboring star.
- Alpha Centauri C (ACC) (Na'vi name: Tawsnrrtsyìp meaning "Little light source in the sky"), also known as Proxima Centauri, is a red dwarf, being only 20% of the size of the Sun and less than half its temperature. ACC gives off only a dim red glow instead of the bright yellow glare of the Sun and ACA. ACC is also about 0.13 light-years closer to Earth.
Planetary Bodies[]
ACA (Rigil Kentaurus)[]
Pandora orbits the gas giant Polyphemus.
Two terrestrial planets and three gas giants orbited around ACA.[3] The rocky planets were the closest to ACA. The three gas giants were named Oceanus, Polyphemus, and Coeus. Here are some further details about these planets:
- Odyssey is the closest planet to the star and is said to be mostly ice surrounding a rocky core, with a chaotic orbit.
- Ulysses, also known as Themis, is the second-closest planet and is mostly ice surrounding a rocky core, with a chaotic orbit.
- Oceanus is the third planet and the closest gas giant to ACA, it is completely covered in water and has a swarm of dozens of moons orbiting it.
- Polyphemus, formerly known as Crius, is the fourth planet and the second closest gas giant to ACA. It is the largest planetary body around ACA and has fourteen moons orbiting it, including Dante, Hades, Pandora, Cassandra, Chaos, Poly-L4, and Poly-L5.
- Coeus is the smallest and outermost gas giant. The planet has two strange moons named Dionysus (19,000 km in diameter) and Bacchus (less than 500 km in diameter). Bacchus spins around Coeus and Dionysus in an unusual "flower petal" orbit.
ACB (Toliman)[]
Alpha Centauri B as seen from Pandora
Five terrestrial planets and three gas giants orbited around ACB. The gas giants were discovered by terrestrial observatories while the rocky planets were discovered two decades later. Since the arrangement of the planets resembled the Solar System, they were named for their counterparts (mentioned in braces):
- Vulcan (Mercury's orbit) is the closest planet to the star and was described as an airless hellscape.
- Hermes (Mercury) is the second closest planet to the star and was described as an airless hellscape.
- Aphrodite (Venus) is the third closest planet to the star and had almost no atmosphere.
- Gaea (Earth) is the fourth closest planet to the star and was said to had undergone a massive greenhouse effect.
- Ares (Mars) is the fifth closest planet and was said to have an atmosphere of 90% nitrogen with too little carbon dioxide for terraforming.
- Zeus (Jupiter) is the sixth closest planet and was the largest planetary body in the entire system.
- Cronus (Saturn) is a gas giant that has a possibility of colliding with Poseidon and had a chaotic orbit.
- Poseidon (chosen instead of another name for Uranus, because it occupies the equivalent of Neptune's orbit) is a gas giant that has a possibility of colliding with Cronus and had a chaotic orbit.
ACC (Proxima Centauri)[]
One close-in gas giant and two terrestrial planets orbited around ACC:[4]
- Unidentified Gas Giant
- Unidentified Rocky Planet 1
- Unidentified Rocky Planet 2
Source[]
- James Cameron's Avatar: The Game - In game Pandorapedia (including French "Planetary Bodies" article from Pandorapedia)
| Planets and Moons | |
|---|---|
| Planets and planetoids | Solar System: Earth ACA: Polyphemus (Poly-L4 and Poly-L5) · Odyssey · Ulysses · Oceanus · Coeus ACB: Vulcan · Aphrodite · Hermes · Gaea · Zeus · Ares · Cronus · Poseidon |
| Moons | Orbiting Polyphemus: Pandora · Cassandra · Hades · Dante · Chaos Orbiting Coeus: Dionysus · Bacchus |