Eight new planets where life could exist found

Eight new planets have been discovered by NASA that exist in the "Goldilocks zone," where the temperature is believed to be at a level water can exists.

Eight new planets have been discovered in the 'Goldilocks' zone of their stars, orbiting at a distance where oceans and life could exist.

The discovery doubles the number of small planets less than twice the diameter of Earth that are believed to be in the habitable zone of their parent stars.

Among these eight, astronomers said there were two that were the most similar to Earth of any known exoplanets to date.

'Most of these planets have a good chance of being rocky, like Earth,' said lead scientist Dr Guillermo Torres, from the Harvard-Smithsonian Centre for Astrophysics in Cambridge, US.

The two most Earth-like planets, known as Kepler-438b and Kepler-442b, both orbit red dwarf stars that are smaller and cooler than the sun.

With a diameter just 12 per cent bigger than Earth, Kepler-438b has a 70 per cent chance of being rocky, the scientists have calculated.

Kepler-442b is about one-third larger than Earth, and the likelihood of it being rocky is around 60 per cent.

To be in the habitable zone, also known as the 'Goldilocks zone', a planet must be not too hot or too cold and receive roughly as much sunlight as Earth.

Too much heat from its star, and any water would boil away as steam. Too little, and the water would freeze solid.

'For our calculations we chose to adopt the broadest possible limits that can plausibly lead to suitable conditions for life,' Dr Torres added.

'For our calculations we chose to adopt the broadest possible limits that can plausibly lead to suitable conditions for life,' Dr Torres added.

Kepler-438b receives about 40 per cent more light than the Earth giving it a 70 per cent probability of having a habitable zone orbit. In comparison, baking hot Venus has twice as much.

The other star gets about two-thirds as much light as Earth and is 97 per cent likely to be in the habitable zone.

Co-author Dr David Kipping, also from the Centre for Astrophysics, said: 'We don't know for sure whether any of the planets in our sample are truly habitable. All we can say is that they're promising candidates.'

Neither of the planets are our close neighbours. Kepler-438b is located 470 light-years from Earth while the more distant Kepler-442b is 1,100 light-years away.

The team, whose findings were presented at the American Astronomical Society's annual meeting in Washington DC, studied planetary candidates first identified by Nasa's Kepler space telescope.

All the planets were too small to confirm by measuring their masses. Instead, they were validated using a computer program that determined they were statistically likely to be planets.

After the analysis, follow-up observations showed that four of the planets were in multiple star systems.

The research is also published in the Astrophysical Journal.

WHAT IS THE GOLDILOCKS ZONE?

The Goldilocks zone is the belt around a star where temperatures are ideal for liquid water to pool on a planet's surface.

To determine the location of a star's habitable zone, scientists have to first learn how much total radiation it emits.

Knowing precisely how far away a habitable zone needs to be from a star also depends on chemistry.

For example, molecules in a planet's atmosphere will absorb a certain amount of energy from starlight and radiate the rest back out.

How much of this energy is trapped can mean the difference between a turquoise sea and erupting volcanoes.

Researchers in Scotland now claim that Earth-sized planets could support life at least 10 times further away from stars than first thought.