Tau Ceti's planets nearest around single, Sun-like star

The nearest single Sun-like star to the Earth hosts five planets - one of which is in the "habitable zone" where liquid water can exist, astronomers say as quoted by BBC.

Tau Ceti's planetary quintet - reported in an online paper that will appear in Astronomy and Astrophysics - was found in existing planet-hunting data.

The study's refined methods of sifting through data should help find even more far-flung worlds.

The star now joins Alpha Centauri as a nearby star known to host planets.

In both those cases, the planets were found not by spying them through a telescope but rather by measuring the subtle effects they have on their host stars' light.

In the gravitational dance of a planet around a star, the planet does most of the moving. But the star too is tugged slightly to and fro as the planet orbits, and these subtle movements of the star show up as subtle shifts in the color of the star's light we see from Earth.

This "radial velocity" measurement is a tricky one; stars' light changes also for a range of other reasons, and requires picking out the specifically planetary component from all this "noise".

Now, Hugh Jones of the University of Hertfordshire and colleagues have refined their "noise modeling" in order to subtract it, and thereby see the smallest signals hiding in the data - starting with Tau Ceti.

"It's a star on which we have a lot of data - an order of magnitude more data than we have for pretty much any other star," Prof Jones told BBC News.

"It's a good test case for how low can we go, what size of signals can we pick up."