Other telescopes in Hawaii showed that the planet has similar properties to those of gas giants orbiting around young stars, but PSO J318.5-22 lacks a host star. Photo / File / Thinkstock
Astronomers say they have found a lonely planet outside the solar system floating alone in space and not orbiting a star.
The gaseous exoplanet, dubbed PSO J318.5-22, is just 80 light years from Earth and has a mass only six times that of Jupiter. Having formed 12 million years ago, the planet is considered a newborn among its peers.
"We have never before seen an object free-floating in space that looks like this. It has all the characteristics of young planets found around other stars, but it is drifting out there all alone," said research team leader Michael Liu of the Institute for Astronomy at the University of Hawaii at Manoa.
"I had often wondered if such solitary objects exist, and now we know they do."
The researchers, whose study was published in the Astrophysical Journal Letters, identified the planet from its faint and unique heat signature using the Pan-STARRS 1 wide-field survey telescope on the Haleakala volcano of Hawaii's Maui island.
They suggested the newly found planet may have the lowest mass of all known freely floating objects.
Other telescopes in Hawaii showed that the planet has similar properties to those of gas giants orbiting around young stars, but PSO J318.5-22 lacks a host star.
During the past decade, researchers have found about a thousand extrasolar planets using indirect methods, including planet-induced wobbling or dimming of their host stars.
But only a handful of these planets have been observed directly since most are orbiting around young stars less than 200 million years old and thus very bright.
PSO J318.5-22 "is going to provide a wonderful view into the inner workings of gas-giant planets like Jupiter shortly after their birth," said co-author Niall Deacon of the Max Planck Institute for Astronomy in Germany.
This artist's rendering shows a comparison between the Earth, left, and the planet Kepler-452b. Photo / AP
Astronomers have found a planet they say is "the closest twin to Earth" ever seen.
Named Kepler-452b, it is the smallest planet discovered orbiting in the habitable zone of a star, and has been described as an "older, bigger cousin".
What makes this planet remarkable is that it orbits its star at about the same distance that Earth orbits the sun. What's more, its home star looks to be similar to our sun.
This Earth-like world has a "substantial opportunity" to host life, Nasa says, adding that if plants were transferred there, they would likely survive.
The planet is about 60 per cent bigger than Earth, and is located about 1,400 light years away in the constellation Cygnus.
Its discovery brings the total number of confirmed planets to 1,030.
Nasa has also found 12 new small habitable zone candidate planets, marking another milestone in the journey to finding another "Earth."
It is "the closest twin to Earth, or the Earth 2.0 that we've found so far in the dataset", said John Grunsfeld, associate administrator of Nasa's Science Mission Directorate.
Kepler-452b is larger than Earth, but its 385-day orbit is only 5 per cent longer.
It resides in something known as the habitable zone - or Goldilocks zone - which is an area around a star where liquid water could pool on the surface of an orbiting planet.
It is also 5 per cent farther from its parent star Kepler-452 than Earth is from the sun.
"This is so fascinating because Kepler 452b receives the same kind of spectrum and intensity of light as we do on Earth," said Dr Daniel Brown, an astronomy expert at Nottingham Trent University.
"This means plants from our planet could grow there if it were rocky and had an atmosphere.
"You could even get a healthy tan like here on holiday. Getting to our closest twin planet might take a while though, since it's 1,400 light years away."
Kepler-452 is 6 billion years old, 1.5 billion years older than our sun, has the same temperature, and is 20 per cent brighter and has a diameter 10 per cent larger.
While its mass and composition are not yet known, previous research suggests that planets the size of Kepler-452b have a good chance of being rocky.
"We can think of Kepler-452b as an older, bigger cousin to Earth," said Jon Jenkins, Kepler data analysis lead at Nasa's Ames Research Center.
"It's awe-inspiring to consider that this planet has spent 6 billion years in the habitable zone of its star' longer than Earth.
"That's substantial opportunity for life to arise, should all the necessary ingredients and conditions for life exist on this planet."
To help confirm the finding and better determine the properties of the Kepler-452 system, the team conducted ground-based observations.
These measurements were key for the researchers to confirm the planetary nature of Kepler-452b, to refine the size and brightness of its host star and to better pin down the size of the planet and its orbit.
"Kepler 452b could be experiencing now what the Earth will undergo more than a billion years from now,' said Doug Caldwell, a Seti Institute scientist on the Keplar mission.
"If Kepler 452b is indeed a rocky planet,' he said, its location 'could mean that it is just entering a runaway greenhouse phase of its climate history.
"Its ageing sun might be heating the surface and evaporating any oceans. The water vapour would be lost from the planet forever."
The research paper reporting this finding has been accepted for publication in The Astronomical Journal.
As well as confirming Kepler-452b, the Kepler team has increased the number of new exoplanet candidates by 521 from their analysis of observations conducted from May 2009 to May 2013, raising the number of planet candidates detected by the Kepler mission to 4,696.
Twelve of the new planet candidates have diameters between one to two times that of Earth, and orbit in their star's habitable zone.
Of these, nine orbit stars that are similar to our sun in size and temperature.
"We've been able to fully automate our process of identifying planet candidates, which means we can finally assess every transit signal in the entire Kepler dataset quickly and uniformly,' said Jeff Coughlin, Kepler scientist at the SETI Institute.
"This gives astronomers a statistically sound population of planet candidates to accurately determine the number of small, possibly rocky planets like Earth in our Milky Way galaxy."
These findings, presented in the seventh Kepler Candidate Catalog, will be submitted for publication in the Astrophysical Journal.
Last year astronomers announced the telescope had spotted its first Earth-sized planet in the habitable zone of another star.
Kepler-186f, which is around 500 light years from Earth, was the first planet to be discovered that is reminiscent of our own.
In January Nasa announced another two new planets - Kepler 438b, which is thought to be only 12 per cent bigger than Earth, and Kepler-442b, which is thought to be 33 per cent bigger.
In July, Kepler spotted five planets orbiting around the same star - Kepler-444 - all of which are thought to be close to the size of Earth.
Paul Hertz, director of astrophysics at Nasa, said identifying worlds that could be home to alien life with Kepler would allow future missions to look at them more closely.
He said: "Future Nasa missions, like the Transiting Exoplanet Survey Satellite and the James Webb Space Telescope, will discover the nearest rocky exoplanets and determine their composition and atmospheric conditions, continuing humankind's quest to find truly Earth-like worlds."
