Life may have evolved on at least three planets in a newly discovered solar system just 39 light years from Earth, scientists believe.
Astronomers have detected no less than seven Earth-sized worlds orbiting a cool dwarf star known as TRAPPIST-1.
The six inner planets lie in a temperate zone where surface temperatures range from zero to 100C.
Of these, at least three are thought to be capable of having oceans, increasing the likelihood of life.
No other star system known contains such a large number of Earth-sized and probably rocky planets.
British astronomer Dr Chris Copperwheat, from Liverpool John Moores University, who co-led the international team, said: "The discovery of multiple rocky planets with surface temperatures which allow for liquid water make this amazing system an exciting future target in the search for life."
A robotic telescope operated by Liverpool John Moores University played a major role in the discovery reported in the journal Nature.
It was one of a number of ground-based instruments that supported observations made by American space agency Nasa's orbiting Spitzer telescope.
The Liverpool telescope helped detect the planets as they passed in front of their star.
Dr Copperwheat said: "As a robotic telescope and the largest in the world, the Liverpool telescope is very sensitive to the small, less-than-1% dips in brightness through which the planets are discovered. It's all automated, it's flexible and fast, and so is ideal for this sort of time critical work."
The planets were found using the "transit" method that looks for tiny amounts of dimming caused by a world blocking light from its star.
The Liverpool Telescope is located on La Palma in the Canary Islands.
Dr Michael Gillon, from the STAR Institute at the University of Liege in Belgium, said: "This is an amazing planetary system - not only because we have found so many planets, but because they are all surprisingly similar in size to the Earth."
TRAPPIST-1, in the constellation Aquarius, is a small star with 8% the mass of the sun and only slightly bigger than the planet Jupiter.
Astronomers expect such dim red dwarf stars to host many Earth-sized planets in tight orbits, making them promising targets in the search for extraterrestrial life.
Other key observations were made by the TRAPPIST robotic telescope at La Silla in Chile, operated from the University of Liege, which is specifically designed to search for transiting planets.
The team determined that all the planets in the system are similar in size to Earth and Venus, or slightly smaller. Density measurements suggest that at least the innermost six are rocky.
Because the star is so dim, the planets are warmed gently despite having orbits much smaller than that of Mercury, the planet closest to the sun.
Three planets classified as TRAPPIST-1 e, f and g orbit in the "habitable" or "Goldilocks" zone where temperatures are not too hot or cold to permit surface oceans of liquid water
Nasa's Hubble Space Telescope is already being used to search for atmospheres around the planets.
Future telescopes, including the European Extremely Large Telescope and James Webb Space Telescope, may be powerful enough to detect markers of life such as oxygen in the atmospheres of exoplanets.
Dr Emmanuel Jehin, another member of the Liege team, said: "We will soon be able to search for water and perhaps even evidence of life on these worlds."
Since the first confirmed exoplanet was discovered in 1992, astronomers have catalogued more than 3,500 worlds in 2,675 star systems.
Around a fifth of sun-like stars are thought to have an Earth-sized planet in their habitable zones.
Astronomers estimate there could be as many as 40 billion potentially habitable worlds in our galaxy, the Milky Way, including those orbiting red dwarfs.