Scientists have discovered at least three new planets in our galaxy that could have allowed life to evolve.

The Earth-sized worlds lie in the "Goldilocks zone" of their sun, where temperatures are not too hot or cold, and are thought to be capable of having oceans of water.

They are in a group of at least seven planets orbiting a dwarf star called Trappist-1, in a newly discovered solar system 39 light years from us. A light year is the distance light travels in a year.

Image: An artist's impression of the surface of Trappist-1f. Pic: NASA/JPL-Caltech

Researchers believe no other known star system contains such a large number of Earth-sized and probably rocky planets.

Trappist-1 lies in the Aquarius constellation and has just under a tenth of the mass of our Sun.


Image: Trappist-1 is an ultra cool dwarf with seven Earth-like planets orbiting it. Pic: NASA/JPL-Caltech

The research, led by NASA and its orbiting Spitzer telescope, was supported by, among others, a robotic telescope operated by Liverpool John Moores University (JMU).

The telescope, which is located in the Canary Islands off the west coast of Africa, helped detect the planets as they passed in front of their star.

Image: Three of the planets - named e, f and g - orbit the 'Goldilocks zone'. Pic: NASA

Dr Chris Copperwheat, part of the JMU 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."

The quest to discover definitively whether life could have been sustained elsewhere in the universe has been intensifying since the first planet outside our solar system was found in 1992.

Image: The automatic telescope. Pic: Astrophysics Research Institute/John Moores University

Since then, astronomers have recorded more than 3,500 worlds in 2,675 star systems.

Just last week, NASA announced it had discovered carbon-based organic material, similar to what may have been the building blocks for life on Earth, on Ceres, a dwarf planet located between Mars and Jupiter.

Image: Scientists are hopeful of finding more planets that could give way to life

In November, the US space agency's New Horizons spacecraft found evidence that Pluto may have a huge ocean hidden under its frozen surface.

The vast site, containing as much water as all of Earth's seas, could also potentially be a habitat for life.