News : Sun-like star and Earth-like planet is found.

Date: 2015-07-25 09:39:05

Sun-like star and Earth-like planet is found.

For the first time a near-Earth-sized planet has been found orbiting a star that is very much like our own sun. NASA on Friday announced the discovery of Kepler-452b, which is 1400 light years from Earth in the constellation Cygnus.

The international team of astronomers working on NASA's Kepler mission that identified the planet includes Daniel Huber of the University of Sydney.

Dr Huber told Fairfax Media that, although more than 1000 exoplanets - those outside our solar system - have been identified, Kepler-452b was special because of the star it orbits and the planet's long orbital period.

An artist's impression of a comparison between the Earth, left, and the planet Kepler-452b. Photo: NASA/Ames/JPL-Caltech/T. Pyle via AP

An artist's impression of one possible appearance of the planet Kepler-452b, the first near-Earth-size world to be found in the habitable zone of a star that is similar to our sun Photo: Reuters

Artist's impression of an earlier discovered exoplanet, Kepler-186f. Unlike Kepler-452b, this planet orbits a cooler red dwarf. Photo: NASA

"Kepler-452b has similar characteristics to our sun, which makes finding a planet with an orbital period similar to Earth in this system very exciting," Dr Huber said. "It is the first time we have found such a planet."

A year on Kepler-452b is 385 days, just 20 days longer than on Earth. The planet is 60 per cent larger than Earth, but its mass is unknown. It may or may not have an atmosphere.

Kepler-452b orbits at 1.05 astronomical units – that means its orbit is only 5 per cent more distant from its star than Earth is from the sun.

"The system is too distant to determine whether it has an atmosphere, so we don't know if it has the right conditions to harbour life," Dr Huber said.

But, based on its radius, the team estimates a better than even chance the planet has a rocky composition rather than being a gaseous planet.

Dr Huber said that most other exoplanets have been found orbiting the more prevalent M-type dwarf red stars. These stars are much cooler than the sun, which is a G2-type star. Kepler-452b is also orbiting a G2-type star.

Because M-type stars are much cooler, their habitable or "Goldilocks" zones are much closer to the stars, meaning that planets in these orbits have much shorter orbital periods. 

G2-type stars such as the sun are much hotter, so the habitable zones are further out. This means that planets in these zones have longer orbital periods, just like Earth ... and now Kepler-452b. Habitable zones are defined as those where planets could have liquid on the surface.

But does it matter? Dr Huber emphatically says yes.

"We have a curiosity to find out whether we are alone. What is our place in the galaxy and the universe?

"Finding out more about exoplanets is Kepler's key mission. We want to find out how abundant Earth-like planets are."

The research that found Kepler-452b was led by Jon Jenkins from NASA's Ames Research Centre. The findings will be published in The Astronomical Journal on Friday.

Dr Huber said that exoplanets are identified using the transit method. The planets themselves are not directly observed but their impact on the brightness of the stars they orbit is closely measured. As the planet passes in front of the star, the brightness dims. The timing and regularity of these transits provides a rigorous method for identifying exoplanets.

Dr Huber, originally from Austria, did his PhD in astrophysics at the University of Sydney. He worked at the Kepler mission in the US from 2011 to 2014 before returning to live and work in Sydney.

"Kepler has shown us that exoplanets are abundant," Dr Huber said. "Now we just need to find if any are supporting life."

This week, Professor Stephen Hawking launched the Breakthrough Initiative, a $US100 million, 10-year mission to find out if we are alone in the universe.

Where the Kepler mission searches for planets in the optical electromagnetic wavelength, Breakthrough will use radio telescopes such as the dish at Parkes to search for tell-tale blips from aliens.