Milky Way 'teeming with billions of Earth-like planets capable of supporting life'

'Nearest Sun-like star with Earth-size planet in its habitable zone is probably only 12 light years away' says scientist

Science Editor

The Milky Way galaxy is teeming with Earth-like planets that are not too hot and not too cold for liquid water to exist at their surface - and so be capable of supporting life, a study has found.

Astronomers have calculated that about one in every five of the billions of Sun-like stars in our galaxy has at least one rocky planet orbiting them at a distance where water is neither frozen solid nor boiled dry.

Knowing how many rocky planets are in the so-called Goldilocks zone - neither too hot, nor too cold - was one of the central goals of the Kepler satellite mission to estimate the total number of "exoplanets" existing beyond the Solar System.

The latest estimate, based on Kepler data, is the most accurate assessment so far of the number of potentially habitable planets in our own galaxy of between 100bn and 400bn stars.

"What this means is, when you look up at the thousands of stars in the night sky, the nearest Sun-like star with an Earth-size planet in its habitable zone is probably only 12 light years away and can be seen with the naked eye. That is amazing," said Erik Petigura of the University of California, Berkeley, who led the research.

The now-defunct Kepler space telescope, launched in 2009, was designed to detect the tiniest changes in a star's brightness as an orbiting planet crosses in front of it. The signal had to be highly repeatable to confirm the existence of an orbiting planet.

The Kepler scientists reported about 3,000 planetary "candidates", estimated by taking photographs every 30 minutes of about 150,000 stars. Many of these planets are much larger than Earth and unsuitable for water and life, such as gaseous giants like Jupiter or those with thick atmospheres like Neptune, or hot planets that orbit much too close to their star.

"This number - that every fifth star has a planet somewhat like Earth - is really important, because successor missions to Kepler will try to take an actual picture of a planet, and the size of the telescope they have to build depends on how close the nearest Earth-size planets are," said Andrew Howard of the University of Hawaii.

The scientists focussed on 42,000 stars that are similar in size and temperature to our own Sun. They found 603 planets orbiting these stars, but only 10 of them were the in the same size-range as Earth and with an orbit suitable for liquid water

The scientists scaled up their analysis to provide a total estimate for the entire galaxy and tested their computer algorithms with fake planets, which were designed to see how many planets were being missed in their analysis.

"What we're doing is taking a census of extrasolar planets, but we can't knock on every door. Only after injecting these fake planets and measuring how many we actually found, could we really pin down the number of real planets that we missed," Dr Petigura said.

It is likely that many of the Earth-size planets in the analysis are still not suitable for life even though they fall in to the habitable zone. Mars and Venus, for instance, are not presently habitable, although liquid water may have existed on them in the past.

"Some may have thick atmospheres, making it so hot at the surface that DNA-like molecules would not survive. Others may have rocky surfaces that could harbour liquid water suitable for living organisms," Professor Geoffrey Marcy at Berkeley.

"The primary goal of the Kepler mission was to answer the question: when you look up in the night sky, what fraction of the stars that you see have Earth-size planets at lukewarm temperatures so that water would not be frozen into ice or vaporised into steam?" Professor Marcy said.

The focus on liquid water is critical because it is widely thought that it is a prerequisite for life, said Professor Marcy, who collaborated on the study published in the journal Proceedings of the National Academy of Sciences.

"Until now, no one knew exactly how common potentially habitable planets were around Sun-like stars in the galaxy," he said.

Start your day with The Independent, sign up for daily news emails
PROMOTED VIDEO
ebooks
ebooksA year of political gossip, levity and intrigue from the sharpest pen in Westminster
Latest stories from i100
Have you tried new the Independent Digital Edition apps?
Independent Dating
and  

By clicking 'Search' you
are agreeing to our
Terms of Use.

iJobs Job Widget
iJobs General

Recruitment Genius: Account Manager

£20000 - £35000 per annum: Recruitment Genius: This full service social media ...

Recruitment Genius: Data Analyst - Online Marketing

£24000 - £35000 per annum: Recruitment Genius: We are 'Changemakers in retail'...

Austen Lloyd: Senior Residential Conveyancer

Very Competitive: Austen Lloyd: Senior Conveyancer - South West We are see...

Austen Lloyd: Residential / Commercial Property Solicitor

Excellent Salary: Austen Lloyd: DORSET MARKET TOWN - SENIOR PROPERTY SOLICITOR...

Day In a Page

Isis in Iraq: Yazidi girls killing themselves to escape rape and imprisonment by militants

'Jilan killed herself in the bathroom. She cut her wrists and hanged herself'

Yazidi girls killing themselves to escape rape and imprisonment
Ed Balls interview: 'If I think about the deficit when I'm playing the piano, it all goes wrong'

Ed Balls interview

'If I think about the deficit when I'm playing the piano, it all goes wrong'
He's behind you, dude!

US stars in UK panto

From David Hasselhoff to Jerry Hall
Grace Dent's Christmas Quiz: What are you – a festive curmudgeon or top of the tree?

Grace Dent's Christmas Quiz

What are you – a festive curmudgeon or top of the tree?
Nasa planning to build cloud cities in airships above Venus

Nasa planning to build cloud cities in airships above Venus

Planet’s surface is inhospitable to humans but 30 miles above it is almost perfect
Surrounded by high-rise flats is a little house filled with Lebanon’s history - clocks, rifles, frogmen’s uniforms and colonial helmets

Clocks, rifles, swords, frogmen’s uniforms

Surrounded by high-rise flats is a little house filled with Lebanon’s history
Return to Gaza: Four months on, the wounds left by Israel's bombardment have not yet healed

Four months after the bombardment, Gaza’s wounds are yet to heal

Kim Sengupta is reunited with a man whose plight mirrors the suffering of the Palestinian people
Gastric surgery: Is it really the answer to the UK's obesity epidemic?

Is gastric surgery really the answer to the UK's obesity epidemic?

Critics argue that it’s crazy to operate on healthy people just to stop them eating
Homeless Veterans appeal: Christmas charity auction Part 2 - now LIVE

Homeless Veterans appeal: Christmas charity auction

Bid on original art, or trips of a lifetime to Africa or the 'Corrie' set, and help Homeless Veterans
Pantomime rings the changes to welcome autistic theatre-goers

Autism-friendly theatre

Pantomime leads the pack in quest to welcome all
The week Hollywood got scared and had to grow up a bit

The week Hollywood got scared and had to grow up a bit

Sony suffered a chorus of disapproval after it withdrew 'The Interview', but it's not too late for it to take a stand, says Joan Smith
From Widow Twankey to Mother Goose, how do the men who play panto dames get themselves ready for the performance of a lifetime?

Panto dames: before and after

From Widow Twankey to Mother Goose, how do the men who play panto dames get themselves ready for the performance of a lifetime?
Thirties murder mystery novel is surprise runaway Christmas hit

Thirties murder mystery novel is surprise runaway Christmas hit

Booksellers say readers are turning away from dark modern thrillers and back to the golden age of crime writing
Anne-Marie Huby: 'Charities deserve the best,' says founder of JustGiving

Anne-Marie Huby: 'Charities deserve the best'

Ten million of us have used the JustGiving website to donate to good causes. Its co-founder says that being dynamic is as important as being kind
The botanist who hunts for giant trees at Kew Gardens

The man who hunts giants

A Kew Gardens botanist has found 25 new large tree species - and he's sure there are more out there