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Tau Ceti System

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Exoplanetary Scratchpad

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The nearest single G-class yellow dwarf to the sun. It has five super-Earth sized planets in orbit around it, discovered using a new and very powerful but also controversial technique, and an outer debris disk with ten times more material than our solar system's Kuiper belt has.

Two of the planets in the Tau Ceti system are located on opposite edges of a very liberally described habitable zone, analogous to Venus and Mars. No planet has as yet been detected near the middle of the habitable zone, in a situation similar to Earth.

Tau Ceti Webpages

Webpages

EV Threads

Tau Ceti in the News

Detection of Asteroid/Comet Fields (July 2004)

paper http://www.pparc.ac.uk/Nw/Ateroid_alley.asp http://www.astrobiology.com/news/viewpr.html?pid=14513 http://www.universetoday.com/forum/index.php?act=ST&f=2&t=3811 http://www.newscientist.com/article.ns?id=dn6123

Detection of Exozodiacal Dust/Inner Debris Disk (February 2007)

paper

seminar paper (powerpoint style)

Possible Planet Detection (When?)

http://planetquest.jpl.nasa.gov/Navigator/ao_support/marcy.pdf

Planet Detections (December 18, 2012)

Tau Ceti Gallery

Tau Ceti Fun Links

Tau Ceti System Factoids

  • Has five exoplanet candidates, all super-Earths (Tau Ceti b, the smallest, with just twice Earth's mass, is estimated to be just about large enough to be classified as a super-Earth). They were detected using a new powerful but controversial technique for compensating for stellar noise when analysing radial velocity measurement. There is a high probability that there are other planets in this system yet to be discovered. Neptune sized planets or larger, further out from Tau Ceti, are quite possible, beyond the frostline/snowline where there is more material for planets to grow. Radial velocity measurements more-or-less preclude planets much larger than Saturn orbiting at a distance inside 5 AU.
  • Tau Ceti e lies on the inner edge of a liberally defined habitable zone and Tau Ceti f lies on the outer edge of the same habitable zone. No planets have yet been detected in the large space between Tau Ceti e and f, in or near the middle of the habitable zone. This could mean that there are either no planets in the middle of the habitable zone or if planets are there they're too small to detect and/or in too eccentric orbits to detect.
  • Older than the Sun (5-10 billion years)
  • Nearest single star system like the Sun, more sun-like than Epsilon Eridani, but still rather small and cool for a yellow dwarf
  • 19th closest star system to the sun at 11.9 light years.
  • One of the only naked-eye stars less luminous than the Sun.
  • A third magnitude star in the constellation Cetus
  • The Sun would appear as a second magnitude star in the constellation Bootes as seen from Tau Ceti.
  • Travels in the "Thick Disk" of the Milky Way, which is older and generally has less metal content than the "Thin Disk" we reside in. Recently, it has been discovered that low metallicity thick disk stars tend to be slightly more likely to host exoplanets, at 14%, when compared to thin disk stars of low metallicity, at 2%.
  • Has an optical companion not bound to it by gravity, just near its line of site from earth.
  • First target of alien broadcast detection attempts by Frank Drake in "Project Ozma" in 1960
  • Because of its proximity and mature age, it is still one of the most targetted star systems in the search for extrasolar life
  • A planet would need to orbit 0.7 AU from Star to receive as much energy from Tau Ceti as Earth does from the Sun.
  • A chain of small (≤super-Earth) planets extending from the inner part of the system to nearly all the way out to its Kuiper belt is necessary for the exozodiacal dust, that has been observed around Tau Ceti, to be a sustained phenomenon (5-10 billion years). A chain of small planets would also neatly explain the nature of the exozodiacal dust, believed to be in the system, which is thought to be very fine with little variation in size, unlike in our system where the zodiacal dust is of varying grain size. With a chain of small planets the dust from the kuiper belt of Tau Ceit is gently and slowly transported inwards. A bit like a slow flowing and gently meandering river only carrying fine silt in suspension, the dust reaching Tau Ceti is highly ground up and consistently small grained.

Tau Ceti (Star) Factoids

  • Less enriched in heavy materials, despite large asteroid fields with 70 percent the Magnesium and Titanium, 60 percent the Aluminium, 50 percent the Silicon and Calcium and barely 40 percent the Iron content in comparison to our Sun. It has been recently discovered that low metallicity stars with higher Silicon, Titanium and particularly Magnesium content, relative to Iron content, tend to be more likely to host exoplanets. However, some scientists theorise that our Sun's unusually low abundance in Aluminium, Silicon and Calcium, relative to Iron, is due to these specific elements having been taken up in the formation of rocky planets, like the Earth, and so they theorise that the relative lack of abundance of these elements relative to Iron, when found in any other sun like stars, would indicate that rocky planets have formed around those stars too. Whether this theory would still hold for sun like stars with very low metallicities, like Tau Ceti, has yet to be proved. Tau Ceti has a lower proportion of Lithium than 82 G. Eridani, another G8V star which has three super-Earths in orbit around it, but higher levels of Lithium than Epsilon Eridani, a K2V star which has a possible gas giant companion in orbit. However, Lithium deficiency is usually associated with stars that have large Gas Giants in orbit and there is no relationship between Lithium deficiency and stars that just have rocky planets or smaller gas giants, like Neptune, in orbit around them. Also, on average, Lithium abundances decline relative to stars' temperatures and 82 G Eridani is slightly warmer than Tau Ceti whereas Epsilon Eridani is colder than Tau Ceti so perhaps the intermediate abundance of Lithium found in Tau Ceti is not that significant.
  • Spectral Type is G8 V. Temperature = 5,344 K
  • Mass is 81% Sun's, Radius is 83% Sun's, Luminosity is 59% Sun's
  • Near twin to Alpha Centauri B in terms of temperature and luminosity.

Tau Ceti Kuiper Belt Factoids

  • Contains at least ten times as much material (1.2 Earth Mass) than the asteroid and kuiper belts in the solar system (0.1 Earth Mass).
  • Extends to about 55 AU, which is similar to the Solar System's Kuiper Belt. First dust disk discovered with a similar extent as most have been much larger.
  • Its extent is similar to the solar systems Kuiper belt, but its mass it ten times as great.
  • Any earth-like planet in the system could not support life due to the frequent massive impacts. However, within a few AU of Tau Ceti initial indications suggest dust levels being slightly lower and therefore possibly fewer cometary collisions are likely taking place within Tau Ceti's habitable zone where the debris dust concentration has been estimated to be about at the same level as in our solar system.
  • As the system is old (possibly 5-10 billion years), it is perhaps surprising that it has such a large protoplanetary disk. Something interesting must have made this debris field so large so late in its history. Or else maybe the solar system is the oddball for having less material. A star may have passed near the sun, stripping away many of its asteroids and comets. Though there is some disagreement about the exact age of Tau Ceti with some recent estimates giving the age as much younger, around 5 billion years old.
  • Star systems with super-Earth or Neptune mass planets are more than 4 times more likely to have a debris disk, like the Kuiper belt around Tau Ceti, than the average for all stars, possibly because debris planetary systems are dynamically stable and include regions that are populated with planetesimals in the formation process where the planetesimals can remain unperturbed over billions of years.

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Tau Ceti b (Unconfirmed) Factoids

  • Inner planet suggested by radial velocity using new technique, adding noise.
  • Period of 13.965 ± 0.02 Days
  • Semi-Major Axis of 0.105 ± 0.006 AU, eccentricity of 0.16 ± 0.22
  • Minimum Mass of 2.00 ± 0.79 Earth Masses

Tau Ceti f (Unconfirmed) Factoids

  • Outer planet suggested by radial velocity data using a new technique, adding noise
  • Period of 642 ± 30 Days
  • Semi-Major Axis of 1.35 ± 0.1 AU with an eccentricity of 0.03 ± 0.3
  • Minimum Mass of 6.67 ± 3.50 Earth Masses

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