An "older cousin" of Earth has been discovered orbiting a distant sun-like star more than 1,000 light years away.
The world is 60pc larger than Earth and lies in the star's "habitable zone" - the orbital region where temperatures are mild enough to be suitable for life.
No one knows if life has evolved on the planet, Kepler-452b. But since the parent star is 1.5 billion years older than the sun, any creatures living there could be far more advanced than they are on Earth.
That makes Kepler-452b a good candidate for scientists involved in the Search for Extra Terrestrial Intelligence (Seti).
On Tuesday, renowned physicist Professor Stephen Hawking helped launch a new €90m project to hunt for radio signals from alien civilisations.
Breakthrough Listen will use two of the world's most powerful radio telescopes to scour thousands of stars for transmissions over 10 years.
News of Kepler-452b's discovery was released by astronomers operating the American space agency Nasa's Kepler space telescope.
Dr Jon Kenkins, from Nasa's Ames Research Centre in Moffett Field, California, said: "We can think of Kepler-452b as an older, bigger cousin to Earth, providing an opportunity to understand and reflect upon Earth's evolving environment.
"It's awe-inspiring to consider that this planet has spent six billion years in the habitable zone of its star; longer than Earth. That's substantial opportunity for life to arise."