“ARE we alone in the universe?

“We’re taking one small step in answering that question today.”

And with that, astronomers hunting for another Earth announced they have found what may be the closest match yet, a potentially rocky planet circling its star at the same distance as the Earth orbits the Sun, NASA said overnight.

“Until about 20-years ago, we didn’t know the answer to that. Now we have a definitive answer.

“Today we’re announcing the discovery of an exoplanet that as far as we can tell, is a pretty close cousin to the Earth and our sun.

“This is about the closest twin to Earth 2.0 that we’ve found so far, and I really emphasise so far.”

Not only is this planet squarely in the Goldilocks zone — where life could exist because it is neither too hot nor too cold to support liquid water — its star looks like an older cousin of our Sun, the US space agency said.

— WHAT WE KNOW SO FAR —

Known as Kepler-452b, the planet was detected by the US space agency’s Kepler Space Telescope, which has been hunting for other worlds like ours since 2009.

“Kepler-452b is orbiting a close cousin of our Sun, but one that is 1.5 billion years older,” NASA said in a statement.

Kepler-452b orbits a parent star, belonging to the same class as the sun, it’s just 4 per cent bigger and 10 per cent brighter. It takes 385 days to orbit the star.

Its radius is 60 per cent larger than Earth with a likely mass five times that of our own.

“You and I would weigh twice as much as we do now on the planet”, said John Grunsfeld, associate administrator for NASA’s Science Mission Directorate in Washington.

“We’d also expect the atmosphere to be thicker and with more cloud cover, with very active volcanoes.”

Kepler-452b’s orbit is nearly the same size of Earth, using ten per cent more energy.

According to NASA, Earth will follow in Kepler’s footsteps and will receive the same amount of energy in 1.5 billion years.

The planet, located in the “habitable zone” of the universe, lies 1,400 light years away.

“We know little about the atmosphere about this planet, it certainly has an atmosphere but details of its composition are totally unknown to us,” said Jon Jenkins, Kepler data analysis lead at NASA’s Ames Research Center in Moffett Field, California.

— IS THERE EVIDENCE OF LIFE ON KEPLER-452B? —

Jenkins was wary about confirming or denying this, adding Kepler’s job description was to “count the number of small planets in our near the habitable zones of sun-like stars” instead of touching down on the planet and searching for alien life.

“The exciting thing is we’ve found so many planetary systems that are unlike our solar system. Signs of life require advanced technology and instruments in space, and so what Kepler is doing is telling us there are world’s out there that we can go forward and pursue following them up.”

— COULD HUMANS LIVE ON THE PLANET? -

“This is humankind’s first step,” said Kepler research scientist Jeff Coughlin.

“It’s a long-term goal but a very exciting one.

“You and I probably won’t be travelling to these planets — but our children’s children could be. This gives us something to aim for.”

“One generation from now we might be able to get there. It gives humankind something to shoot for.”

Coughlin went on to say that Mars was the next closest habitable planet in our solar system.

— IS THERE EVIDENCE OF LIFE IN THE UNIVERSE? -

“We’re listening in to see if anyone is broadcasting (from another planet), using radio waves,” said Jeff Coughlin, Kepler research scientist at SETI Institute in Mountain View, California.

“That’s a hard question to answer, we’re taking steps about as aggressively as technology will permit.

“We really don’t know what (a civilisation) would use, if there is something better than radio.

“We’ll stick with what we do know and keep listening. If down the road we find something better we’ll use that.”

The team detailed the difficulties in reaching such universes, and the hurdles in finding extraterrestrial life.

Want to get quickly up to speed on the search for earth-lilke planets? Try this! http://t.co/GhrYLQjAo5 pic.twitter.com/15kKbuOj3b — NASA Kepler (@NASAKepler) July 23, 2015

“Before we get pictures of the sorts we just got from Pluto, where we fly-by a distant exoplanet and beam back to Earth the images, the speed at which the aircraft can get there, the speed of light, is many decades.

“First we have to discover the planets, but we can learn a lot from surveillance.

“If we had a sufficiently large telescope with current technology we could make the first primitive maps of an Earth-like planet.

Whether they have oceans, clouds, perhaps even seasons and start characterising what those planets are like.

“Whether we can discover life is a tricky question, would we recognise those signs of life?

“Those kinds of telescopes might be able to do that as well.”

— GLIMPSE INTO APOCALYPTIC FUTURE —

The planet, which is 1,400 light-years away, could offer a glimpse into the Earth’s apocalyptic future, scientists said.

Its star is four per cent more massive than the Sun and 10 per cent brighter. If the planet is rocky, and scientists believe that it has a better than even chance of being just that, then it could be in the midst of a fearful scenario, as the heat from its dying star evaporates Kepler-452b’s lakes and oceans.

“If Kepler-452b is indeed a rocky planet, its location vis-a-vis its star could mean that it is just entering a runaway greenhouse phase of its climate history,” said Doug Caldwell, a Search for Extraterrestrial Intelligence (SETI) Institute scientist working on the Kepler mission.

“The increasing energy from its ageing sun might be heating the surface and evaporating any oceans. The water vapour would be lost from the planet forever,” he added.

“Kepler-452b could be experiencing now what the Earth will undergo more than a billion years from now, as the Sun ages and grows brighter.”

- PLANETARY CATALOGUE —

The Kepler mission launched in 2009 to search for exoplanets, which are planets outside our solar system, particularly those about the size of Earth or smaller.

“Today, and thousands of discoveries later, astronomers are on the cusp of finding something people have dreamt about for thousands of years — another Earth,” NASA said in a statement.

On Thursday, NASA released the latest catalogue of exoplanet candidates, adding more than 500 new possible planets to the 4,175 already found by the space-based telescope.

“This catalogue contains our first analysis of all Kepler data, as well as an automated assessment of these results,” said SETI Institute scientist Jeffrey Coughlin.

The new catalogue includes 12 candidates that are less than twice the diameter of Earth and which are orbiting in the habitable zones of their stars.

Of those 12 new candidates, Kepler-452b “is the first to be confirmed as a planet,” NASA said.

Kepler identifies possible planets by watching for dips in the brightness of stars, which could be caused by a planet passing between the star and the telescope.

Other scientific tools are needed to judge whether the planet is gassy or rocky. The Kepler mission has cost NASA about $600 million, and the US space agency said in 2013 that two of its orientation wheels had lost function, leaving the space telescope beyond repair.

But scientists have years to pore over the data it has returned in order to narrow the search for Earth-like worlds.

- Additional reporting by AFP