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Tau Ceti System

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Exoplanetary Scratchpad

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Tau Ceti is also known as HD 10700, HR 509, and Gl 71. The nearest single G-class yellow dwarf to the sun, somewhat smaller than the Sun. A popular science fiction subject and one of two targets of SETI-forerunner Project Ozma in the 1960s. Despite being somewhat older than the sun, it has an extensive asteroid and/or comet field 10-50 AU, with the bulk between 35 and 50 AU. It has about ten times as much material as the Sun. This would make life difficult. It is a metal deficient star, so it is thought less likely to host rocky planets. Traditional dopplar spectrometry has ruled out any large Jupiter sized planets at Jupiter like distances or closer in, which was thought to be good for any potentially habitable planets. Five candidate rocky super Earth planets were detected though using a new method of planetary detection. This method made predictions of the stellar "noise" activity that might obscure detection of a planet based on the long history of dopplar measurements done on this system. Deviations from this prediction pointed towards the existence of planets. Confirmation using more established methods is needed. These planets are labeled b through f as you go outward, span 0.1 AU to 1.35 AU, and get larger the further you go out (at least 2 ME to 6.6 ME). The outermost two are near the habitable zone and were originally hailed as possibly being the nearest and smallest known habitable planets. More recent modeling indicates they are not actually habitable though. Planet e is probably too close to the star and only in the HZ if generous assumptions are made. Planet f has probably only been in the habitable zone for about a billion years as a result of its star becoming hotter, which might make biosigns difficult to detect from Earth, considering it took 2 BY for biosigns to become detectable around the Earth. Since the star has a higher magnesium to silicon ratio than the Sun, these planets compositions could be quite different that the Solar System's. The lower mantles could be dominated with ferropericlase, which is not very viscious, which may make the rocks of the mantle flow easier than on Earth, affecting volcanism and tectonics. One of 5 PICTURE-C targets selected for sub-orbital coronograph observation.

My ThoughtsEdit

I wonder if we should be considering the Tau Ceti system, the nearest yellow dwarf star to the sun, to be a representative of the most common type of yellow dwarf systems. Recent studies suggest that the solar system is rather atypical. Most stars seem to have a lot of close in super Earth planets from the habitable zone towards much closer than Mercury. Our Solar System may have once had such planets, which were more massive than the Earth, but likely had dense atmospheres, but the formation of Jupiter and Saturn caused them to spiral into the Sun. This systems seems to lack a Jupiter, so this could be what the solar system might be like if we didn't have Jupiter. I surmise that with an asteroid/comet belt out past Jupiter-like distances, we might simply have no giant planets in the system at all. I'll be interested to see if we do find a large planet, perhaps just inside of the comet belt. I'm now wondering how other nearby yellow dwarf stars compare. 82 G. Eridani System is the nearest single yellow dwarf star with confirmed planets, and it seems to have a similar layout to Tau Ceti - 3 super Earths at similar distances as Tau Ceti's innermost 3 and a dust belt at large distances. I wonder how typical the high magnesium to silicon ratio in this system is also.

I also see that earlier papers thought that such an extensive debris disk would make it tough for life to develop, with too many collisions. But would these asteroids and comets end up in eccentric orbits without a large planet scattering them? Could they be scattered by the super earths? But would you end up with them being at risk any more than the solar system is?

It's debris disk was also thought to be really rare, especially for such an old star. But when I look at other nearby sun-like stars with planets, I see there's also debris disks around them, and a similar lack of Jovians. Maybe it was just the easiest and earliest detected debris disk like that.

Tau Ceti WebpagesEdit

Webpages

EV Threads

Tau Ceti in the NewsEdit

Detection of Asteroid/Comet Fields (July 2004)Edit

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

paper

Possible Planet Detection (Dec 2012)Edit

Selected As PICTURE-C Suborbital Coronograph TargetEdit

See Vega System, Alsafi System, Epsilon Eridani System, Altair System, Tau Ceti System

Modeling Suggests Planetary Candidates Not So Life Friendly (Apr 2015)Edit

Tau Ceti GalleryEdit

Tau Ceti Fun LinksEdit


Tau Ceti System FactoidsEdit

  • Two unconfirmed exoplanet candidates
  • Much older than the Sun (10 BY)
  • 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 has less metal content than the "Thin Disk" we reside in.
  • 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.

Tau Ceti (Star) FactoidsEdit

  • Less enriched in heavy materials, despite large asteroid fields with 70 percent the Magnesium, 50 percent the Silicon and barely 40 percent the Iron in comparison to our Sun.
  • 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 FactoidsEdit

  • 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 very old (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.
  • No evidense of planets has been announced at this time.

Tau Ceti b (Unconfirmed) FactoidsEdit

  • Inner planet suggested by radial velocity data
  • Probably doesn't exist
  • Period of 19.3 Days
  • Semi-Major Axis of 0.15 AU
  • Minimum Mass of 15 Earth Masses

Tau Ceti c (Unconfirmed) FactoidsEdit

  • Outer planet suggested by radial velocity data
  • Probably doesn't exist
  • Period of 61 Days
  • Minimum mass of 19 Earth Masses
  • Semi-Major Axis of 0.33 AU

See AlsoEdit

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