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Tau Ceti system is the planetary system around Tau Ceti, located approximately 11.9 light-years away in the constellation Cetus in the caelregio Hippocampus. There are 13 planets, five were discovered on December 19, 2012.
Tau Ceti, like our Sun, is a G-type main sequence star, but it is fainter, smaller, cooler than our Sun. It is also metal-deficient relative to our Sun as the star contains just 28% as much metals as our Sun based on iron. Tau Ceti is over a billion years older than our Sun, 5.8 Gyr vs. 4.6 Gyr.
Tau Ceti's high proper motion is typical of nearby stars. Tau Ceti would still require 2000 years to transverse about a degree and about 1000 years to transverse the diameter of the full moon.
Planetary system Edit
|Class||Semimajor axis (AU)||Eccentricity||Orbital period (yr)||Radius||Mass||Density (g/cm3)||Gravity (g)||Rotation period (d)||Surface temp (K)|
|Penthus (b)||LEaV||0.15761||2.0966 M⊕||6.347||1.405|
|Zeus (c)||BeaV||0.03412||3.2433 M⊕||5.394||1.459|
|Hades (d)||DEaH||0.07714||3.6557 M⊕||6.876||1.784|
|Aita (e)||SDBEaC||0.05455||4.4839 M⊕||6.946||1.923|
|Poseidon (f)||SiOEaM||0.02673||6.9204 M⊕||6.901||2.213|
Tau Ceti contains one of the biggest family of planets in the solar neighborhood as it is orbited by 13 planets, merely five more than our Sun has. The planets range in orbital periods from about two weeks to seven centuries and distances ranging from 0.1 AU to 73 AU, considerably wider in range than our solar system in both categories. This system has similar average eccentricity amongst the planets (0.0652) as there are in our solar system (0.0603). There are two trojan planets in this system, a pair at 0.86 AU and a pair at 12.13 AU, both orbiting 60° of each other.
This system contains seven terrestrial planets, all within 1.35 AU, and six giant planets, all orbiting at least 6.4 AU. There is a debris disk orbiting 35–50 AU, locked between the orbits of two massive planets, one touching the inner edge while the outer veer through outer two-third of the region.
Detected planets Edit
Penthus (tentatively Tau Ceti b) is the innermost planet of the Tau Ceti system. It is the super-Earth massing 2.1 Earth masses, just above the lower limit of super-Earth. It is also larger and denser than Earth. The planet is tidally-locked to the sun, meaning its rotation period is exactly the same as its orbital period. It takes 13.7 days to rotate once on its axis while it takes 13.7 days to orbit the sun.
As is the case for most innermost planets, Penthus is the hottest planet in this system with the surface temperature of 962°F. Tidal forces of the parent star may melt the interior of Penthus, making the world volcanically active with lava covering much of the surface.
Zeus (tentatively Tau Ceti c) is a barren world about 50% bigger than Earth and over three times the mass of our planet. The density of Zeus is similar to three of four terrestrial planets of our solar system. It takes over a month to revolve around the star and takes 41⁄2 weeks to rotate once on its axis, about the same as rotation of our Moon.
Hades (tentatively Tau Ceti d) is a super-Earth orbiting at Mercury-like distance from the star and is almost seven times the density of water. It is a desert planet with the surface temperature of 165°F, surrounding by the atmosphere about half as thick as Earth's. Its surface temperature of 5°F warmer than its equilibrium suggests that the atmosphere of Hades contains very little greenhouse gases like carbon dioxide. The planet appears tan from space, reflecting about half of all sunlight falling onto the planet.
Aita (tentatively Tau Ceti e) is a 4.5-Earth mass planet orbiting at 55% the distance between Earth and the Sun or roughly halfway between the orbits of Mercury and Venus. The density is a bit more than Earth's and surface gravity approaching twice that of Earth.
Aita is qualified as a sulfur planet because sulfur is abundant on the surface, interior, and atmosphere. The atmosphere is 25 times thicker than Earth's comprising mainly of CO2, SO2, and H2S. The average surface temperature is 142°F.
Poseidon (tentatively Tau Ceti f) is a super-Earth orbiting at 1.35 AU from Tau Ceti, taking 21 months to orbit the star compared to 12 months for Earth. It weighs seven times as much as Earth while it is ¾ bigger than Earth. Poseidon's density 6.9 g/cm3, compared to 5.5 g/cm3 for Earth. The weight of an average person would weigh about 330 pounds on Poseidon, compared to just 150 pounds here on Earth. Poseidon rotates in the opposite direction of its orbit, taking 74 hours 51.8 minutes to complete one backward spin.
Water covers about 54% of the surface of Poseidon, named after the God of the Sea. The surface temperature is 107°F, but the equilibrium temperature is just –133°F. The greenhouse effect must have raised the temperature this much and the atmosphere contains abundant amounts of carbon dioxide, methane, and water vapor. The atmosphere of Poseidon is nine times thicker than Earth's.
Conjectured planets Edit
Tau Ceti g Edit
Tau Ceti g is a planet contain half as much matter as Earth orbiting at 0.86 AU from the star. The density is about 60% that of Earth and its surface gravity half the strength of Earth's. The planet takes 329 days to revolve around the star, 36 days short of an Earth year. The planet rotates on its side with an axial tilt of 79.4° and complete its rotation in 3.66 days (87.8 hours).
Tau Cet g is an ice planet with the surface temp of –51°F and its atmosphere is only 1⁄5 the thickness of Earth's. Almost all ice planets appear white, as is the case for this planet.
Tau Ceti h Edit
Tau Ceti h is a planet sharing the same orbit as g, orbiting at 60° behind that planet. The surface of h is quite different than g as the surface of h is rocky while g is icy. The h's surface temp of 596°F is much higher than g due to much thicker atmosphere and high amounts of greenhouse gases.
Tau Ceti h is a little bit bigger than Earth and the mass classification still places this at the same category as Earth, mid-Earth, as the planet's mass of 1.67 Earth masses is short of upper limit at 2 Earth masses.
Tau Ceti i Edit
Tau Ceti i is a gas giant orbiting at 6.42 AU, taking more than 181⁄3 years to revolve once around the star. The planet takes 171⁄4 hours to rotate once on its axis and the upper clouds are made predominantly of ammonia with water clouds and ammonium hydrosulfide clouds underneath it. The planet's surface temperature (at 1-bar layer) is about the same as Jupiter's. Tau Cet i is bigger and more massive than Jupiter, though still placed in the same mass category as Jupiter.
Radial velocity monitoring of the parent star loosely rule out any giant planets with orbital periods less than 15 years, corresponding to the semimajor axis of under 5.6 AU. This planet's orbital period is just beyond that limit, so hopefully this planet shall be detected in the near future when the limit extends to more than 18 years.
Tau Ceti j Edit
Tau Ceti j is a Saturn-mass planet orbiting more than 12 AU from the star and takes 47¾ years to revolve once around the star in an eccentricity just half the value of Earth's. There are few wisps of visible rings surrounding the planet. The planet appears green due to mixed amounts of methane and ammonia clouds. It takes 18 hours to complete its rotation.
Tau Ceti k Edit
Tau Ceti k is a planet the same size as Jupiter orbiting 60° ahead of Tau Cet j. Its rotation period is twice as short as j, at just over nine hours, slightly shorter than Jupiter's rotation period. Due to its greater mass which correspondingly have more intense internal heating caused by gravitational contraction, this planet's surface temp is raised to –264°F.
Tau Ceti l Edit
Tau Ceti l is a super-Jupiter orbiting at 31 AU from the star, about the same distance as the orbit of Neptune. The orbital period is 1961⁄2 years and eccentricity is moderate (0.127). Despite it is this far from the sun, intense internal heating raise the planet's temperature to as high as 216°F. The planet appears deep blue from space and is over 61⁄3 times more massive than Jupiter and density approaching 5 g/cm3. The planet takes over 9 hours to rotate once on its axis and surface gravity is 111⁄4 times greater than Earth's and 41⁄4 times greater than Jupiter's. A 150-pound person on Earth would weigh about 1760 pounds on Tau Ceti l.
Due to its high mass and gravity, the planet sculpts the inner region of the debris disk, thus its elliptical path would touch the innermost regions.
Tau Ceti m Edit
Tau Ceti m is a super-Jupiter orbiting at 50 AU from Tau Ceti. It masses 3.2 Jupiters and is smaller than Jupiter despite its lot greater mass, producing this gas giant's density about the same as that of Earth, but its surface gravity is nearly 10 times that. This small size relative to mass is due to gravitational contraction, which produces heat that in turn warms up the planet. The produced heat raises the planet's temperature by more than 450°F to 47°F.
Tau Ceti m, due to its high mass, is effeciently sculpting the outer rim of debris disk. It sometimes capture objects to become moons. The presence of the massive planet is preventing objects in the debris disk from forming dwarf planets like Pluto. In addition, Tau Cet m has an eccentric orbit, which would veer through debris disk as distance from the star ranges from 40–60 AU.
Tau Ceti n Edit
Tau Ceti n is the outermost planet of the Tau Ceti system. This sub-Jupiter takes 700 years to revolve around the star at an average distance of 72.7 AU (10.9 gigameters or 6.76 billion miles). The planet takes 161⁄3 hours and its year is about 375500 planetary days. This planet is similar in mass, size, density, and surface gravity to Saturn, but it is much colder. Unlike Saturn, which is tannish yellow, Tau Cet n is blue, due to methane presence.