A new study by an international team of scientists has discovered that the star Tau Ceti may have five planets orbiting it. Tau Ceti is the 20th closest star to the sun, and the nearest star to have sun-like properties. The star has the same spectral classification as the sun, with a mass 78% that of the sun's. It lies only about 12 light-years from Earth.
The study, published in the journal Astronomy & Astrophysics, estimates that the five planets have masses between two and six times that of Earth. This makes it the lowest-mass planetary system yet discovered. One of the planets, with a mass of about five times that of Earth, lies in the habitable zone of the Tau Ceti system, the smallest planet yet found in the habitable zone of a sun-like star.
The habitable zone of a star is defined as the area around a star where a planet could have liquid water on its surface. Just because a planet lies in the habitable zone of a system doesn't mean it is Earth-like, however. Both Mars and Venus are within the habitable zone of our solar system, though their atmospheres don't allow for liquid water.
“We are now glimpsing for the first time the secrets of our nearest companion stars and their previously hidden reservoirs of potentially habitable planets,” said Paul Butler, an astronomer at the Carnegie Institution for Science. “This work presages the time when we will be able to directly see these planets, and search them for water, carbon dioxide, methane, and other signposts of life.”
Astronomers used a new technique to detect the planets, applying "intensive" modeling to data collected from over 6,000 observations of Tau Ceti. The research team was able to find signals half the size of what was previously possible, increasing the sensitivity of small planet searches and discovering Tau Ceti's satellites.
“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,” said Mikko Tuomi, who led the team from the University of Hertfordshire. “This significantly improved our noise modeling techniques and increased our sensitivity to find low mass planets."
Tau Ceti was chosen, say the astronomers, because it was though Tau Ceti had no planets and would be a good benchmark for the new technique. The researchers suggest that due to Tau Ceti's close proximity, the atmospheres of the newly discovered planets could be analyzed in the near future.