When I started writing here many years ago, I didn’t think news of an exoplanet in a star’s habitable zone would become so commonplace that we might not even cover it. Yet here we are a few years later, adding yet another potentially habitable planet to the growing tally. A recent estimate puts the chance of finding a planet in the habitable zone of any given star in our galaxy at one in ten. Now we know one of those nearby stars (Tau Ceti) has five orbiting exoplanets, and two of them might sustain life.
Hugh Jones, Mikko Tuomi, and others at the University of Hertfordshire estimate that our twentieth-closest stellar neighbor, Tau Ceti, is orbited by five exoplanets with nearly circular orbits. The outermost two exoplanets (Tau Ceti e and Tau Ceti f) are potentially habitable. Their star, Tau Ceti, is the same less-common type of star (G-class) as our own sun, with a mass and radius about 25% less than our sun. The star is about one billion years older than the sun and is very stable. Oh, and it’s only 11.9 light years from Earth, meaning they’re just now getting the first seasons of Six Feet Under, Smallville, and 24.
Tau Ceti e falls clearly within the Core Habitability Zone, that being the region within which a planet like Earth will have liquid water. The Planetary Habitability Laboratory (U Puerto Rico, Arecibo) notes that both Tau Ceti e and f fall within the Extended Habitability Zone where larger planets with thicker atmospheres might retain sufficient heat for water to be liquid. [Gizmag]
Tau Ceti e has a mass of 4.3 Earths and orbits once every 168 days, while Tau Ceti f has a mass of 6.6 Earths and orbits once every 642 days. Unfortunately, their star has few metals and there is over tenfold the amount of comets and asteroids in the system, meaning the exoplanets are probably not rocky like Earth and may be frequently bombarded, making habitability less likely.
Dr. Toumi stated, “I do not consider this particular planet to be very likely to have a rocky surface. It might be a ‘water world,’ but at the moment it’s anybody’s guess.” A water world you say? That settles it. We need to load Kevin Costner into a rocket and blast him into space immediately. This may or may not be related to scientific research. Perhaps I’m just still angry about the three hours I wasted on The Postman.
[Sources: Gizmag, io9, Neatorama; Original paper published in Astronomy and Astrophysics]