Potentially Habitable ‘Another Earth’ Found Orbiting Tau Ceti

Astronomers led by Dr Mikko Tuomi of the University of Hertfordshire have discovered that the nearby star Tau Ceti may host five exoplanets – with one in the habitable zone.

This image shows the nearby star Tau Ceti (Centre de Données astronomiques de Strasbourg / SIMBAD)

Tau Ceti is the closest single star that has the same spectral classification as our Sun. It is located about 12 light-years away in the constellation of Cetus.

The astronomers combined more than six-thousand observations from three different instruments and intensively modeled the data. Using new techniques, they have found a method to detect signals half the size previously thought possible. This greatly improves the sensitivity of searches for small planets and suggests that Tau Ceti is not a lone star but hosts a rich planetary system.

“We pioneered new data modeling techniques by adding artificial signals to the data and testing our recovery of the signals with a variety of different approaches. This significantly improved our noise modeling techniques and increased our ability to find low mass planets,” explained Dr Tuomi, who co-authored a paper to be published in the journal Astronomy & Astrophysics (arXiv.org version).

Tau Ceti’s five planets are estimated to have masses between two and six times the mass of the Earth – making it the lowest-mass planetary system yet detected. One of the planets lies in the habitable zone of the star and has a mass around five times that of Earth, making it the smallest planet found to be orbiting in the habitable zone of any Sun-like star.

This is an artist’s impression of the Tau Ceti system (J. Pinfield / RoPACS Network / University of Hertfordshire)

“We chose Tau Ceti for this noise modeling study because we had thought it contained no signals. And as it is so bright and similar to our Sun it is an ideal benchmark system to test out our methods for the detection of small planets,” said co-author Dr Hugh Jones.

“Tau Ceti is one of our nearest cosmic neighbors and so bright that we may be able to study the atmospheres of these planets in the not too distant future. Planetary systems found around nearby stars close to our Sun indicate that these systems are common in our Milky Way Galaxy,” added Dr James Jenkins of the Universidad de Chile and the University of Hertfordshire.

“This discovery is in keeping with our emerging view that virtually every star has planets, and that the galaxy must have many such potentially habitable Earth-sized planets. They are everywhere, even right next door!” said co-author Dr Steve Vogt of the University of California Santa Cruz.

“We are now beginning to understand that Nature seems to overwhelmingly prefer systems that have a multiple planets with orbits of less than one hundred days. This is quite unlike our own Solar system where there is nothing with an orbit inside that of Mercury. So our Solar system is, in some sense, a bit of a freak and not the most typical kind of system that Nature cooks up.”

“As we stare at the night sky, it is worth contemplating that there may well be more planets out there than there are stars … some fraction of which may well be habitable,” said co-author Dr Chris Tinney of the University of New South Wales.

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Bibliographic information: M. Tuomi et al. 2012. Signals embedded in the radial velocity noise. Accepted for publication in the Astronomy and Astrophysics; arXiv: 1212.4277