From BBC News:
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 team started with data from three planet-hunting missions: Harps, AAPS, and HiRes, all of which had data on Tau Ceti.
The trick to honing the technique was to put in "fake planets" - to add signals into the messy data that planets should add - and find ways to reduce the noise until the fake planets became more and more visible in the data.
"Putting all that together, we optimised a noise-modelling strategy which allows us to recover our fake signals - but in the process of doing that, we actually saw that we were finding signals as well," Prof Jones said - actual planets.
The quintet includes planets between two and six times the Earth's mass, with periods ranging from 14 to 640 days.
One of them, dubbed HD 10700e, lies about half as far from Tau Ceti as the Earth is from the Sun - and because Tau Ceti is slightly smaller and dimmer than our Sun, that puts the planet in the so-called habitable zone.