NASA scientists discover 'Earth's older cousin'

More than a thousand light years away, the Earth's "bigger, older, cousin," is orbiting a star very similar to the sun, scientists said Thursday.

Kepler-452b is the first Earth-like planet to be found orbiting in the habitable zone of a sun-like star.

NASA scientists announced the discovery at a teleconference on Thursday morning.

"Today the Earth is a little less lonely, because there's a new kid on the block," said Jon Jenkins, the Kepler data analysis lead at NASA's Ames Research Center.

Though Kepler-452b is about 60 per cent larger than Earth, its relationship to a sun-like star makes it the most Earth-like planet that's ever been discovered, Jenkins and his colleagues said.

"Today we're announcing the closest twin to Earth, or the closest Earth 2.0 that we have found up to this point," said John Grunsfeld, the associate administrator for NASA's Science Mission Directorate in Washington.

This artist's concept depicts one possible appearance of the planet Kepler-452b, the first near-Earth-size world to be found in the habitable zone of star that is similar to our sun. (NASA / JPL-Caltech / T. Pyle)

The Kepler mission

The discovery is the latest find from the Kepler Space Telescope. Launched in 2009, the Kepler mission is dedicated to finding habitable planets in other solar systems.

Habitable planets are able to host water as a liquid because they orbit far enough from stars that it won't evaporate, but close enough it won't freeze.

In addition to looking for planets orbiting in habitable zones, scientists are looking for terrestrial planets, which are similar in size to earth, and for planets with rocky surfaces.

These conditions all make a planet more capable of supporting life.

This artist rendition provided by NASA shows the Kepler space telescope. (AP / NASA)

Earth's 'bigger' cousin:

Scientists say the recently-found Kepler-452b measures about 1.6 earth radii, and they believe it has a mass about five times greater than Earth.

While NASA can't confirm what the surface area looks like, it says the planet's large size makes it likely to be rocky. If that's the case, then scientists say the planet likely has many volcanoes, and an atmosphere that is thicker and cloudier than the Earth's.

"If you travelled to this star with an ark full of plants and animals, we'd hope that it'd be rocky," Jenkins said.

If it was, he said, plants would be able to grow, as the starlight on Kepler-452b is similar to the sun's light on Earth.

"The sunshine from the star is very similar to the sunshine from our own star, and so the plants would photosynthesize just fine," he said. "It would feel a lot like home."

A sun-like star

Like the sun, Kepler-452b's closest star is considered a G-2 type star, though at 6 billion years old, it's been around 1.5 billion years longer than the sun.

Another similarity to Earth is that Kepler-452b takes 385 days to circle its star, not much longer than the Earth's 365-day cycle.

A long way from home

Despite the similarities, Kepler-452b is still a long way from home.

Scientists said Thursday that it is highly unlikely anybody alive today would be able to visit the distant planet.

"The furthest we've travelled is our own moon, which is incredibly close, relatively speaking," said Jeff Coughlin, a Kepler research scientist at the Search For Extraterrestrial Intelligence Institute.

While the moon is only a few light seconds from Earth, Coughlin explained, Kepler-452b orbits in a solar system 1,400 light years away, a distance humans aren't likely to cross for generations.

"You and I won't be travelling to this planet," Coughlin said "But our children's, children's, children's might be."

"This is really the first step."