In our search for alien life, the most likely planets in the universe that potentially host life are, more than likely, those that exist within their star's habitable zones, as well as those that are most like Earth.

Now, scientists believe they've found what could be an "Earth 2.0," a planet slightly older and larger than Earth that has been in its star's habitable zone for nearly 6 billion years. As that's plenty of time for life to have formed and evolved, that makes this newly discovered planet a likely candidate for potentially hosting life.

By studying data collected by Kepler during its planet-finding mission, scientists discovered this new planet, Kepler-452b, along with its star Kepler 452 in the Cygnus constellation. Further research using ground-based telescopes confirmed the existence of the planet and its star, placing Kepler-452b in the habitable zone. The habitable zone is that sweet spot where planets reside that allows them to have the right temperatures for liquid water to exist on their surface, meaning that the potential for life exists there.

Thanks to this new discovery, now Kepler has helped us discover a total of 1,030 planets, but Kepler-452b, which is about 1,400 light-years from Earth, stands out because it's the smallest we've found so far, putting it closer to Earth's size than other previously discovered planets.

"On the 20th anniversary year of the discovery that proved other suns host planets, the Kepler exoplanet explorer has discovered a planet and star which most closely resemble the Earth and our sun," says NASA's John Grunsfeld, associate administrator of the agency's science mission directorate.

Although Kepler's diameter is about 60 percent larger than Earth's, it still has other things in common with our home planet. For one thing, it's likely that Kepler's surface is rocky, much like Earth. Kepler's's orbit around its star is also similar to Earth's orbit around the sun: it's only about 5 percent longer, taking 385 as compared with 365 days. Finally, Kepler is only about 5 percent farther away from its star than the Earth is from the sun.

The similarities don't stop there, though. Even Kepler's's star is similar to our sun: it's only about 1.5 billion years older, and its temperature is about the same. However, star Kepler 452 is 20 percent brighter and about 10 percent bigger than our sun.

"We can think of Kepler's as an older, bigger cousin to Earth, providing an opportunity to understand and reflect upon Earth's evolving environment," says Jon Jenkins, NASA's Kepler data analysis lead. "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."

Photo: NASA | JPL-Caltech | T. Pyle