A haul of planets from Nasa’s Kepler telescope includes a world sharing many characteristics with Earth.
Kepler-452b orbits at a very similar distance from its star, although its radius is 60% larger.
Its sun is of similar size and brightness to our own, but much older.
Such worlds are of interest to astronomers because they might be small and cool enough to host liquid water on their surface – and might therefore be hospitable to life.
Scientists looking at data from the Kepler observatory have announced the discovery of 500 new possible planets around distant stars.
These join the 4,175 planet candidates already identified by the telescope, excepting the new haul. Historically, most of Kepler’s discoveries have later been confirmed as actual exoplanets.
Twelve of the new candidates are less than twice Earth’s diameter, orbiting in the so-called habitable zone around their star.
This zone refers to a range of distances at which the energy radiated by the star would permit water to exist as a liquid on the planet’s surface.
Of these candidates, Kepler 452b is the first to be confirmed as a planet.
Dr Suzanne Aigrain, from the University of Oxford, who was not involved with the study, told BBC News: “I do believe the properties described for Kepler 452b are the most Earth-like I’ve come across for a confirmed planet to date.”
“What seems even more significant to me is the number of planets in the habitable zone of their host stars with radii below two Earth radii; 12 is quite a few compared to the pre-existing Kepler planet catalogue.
“It bodes well for their attempts to provide a more robust measure of the incidence of Earth-like planets, which is the top-level goal of the Kepler mission.”
While similar in size and brightness to the Sun, Kepler 452b’s host star is 1.5 billion years older than ours. Scientists working on the mission therefore believe it could point to a possible future for the Earth.
“If Kepler 452b is indeed a rocky planet, its location vis-a-vis its star could mean that it is just entering a runaway greenhouse phase of its climate history,” explained Dr Doug Caldwell, a Seti Institute scientist working on the Kepler mission.
“The increasing energy from its aging sun might be heating the surface and evaporating any oceans. The water vapour would be lost from the planet forever.”
“Kepler 452b could be experiencing now what the Earth will undergo more than a billion years from now, as the Sun ages and grows brighter.”
Dr Don Pollacco, from Warwick University, who was not involved with the latest work, told the BBC: “Kepler data allows you to estimate the relative size of a planet to its host star, so if you know the size of the host, hey presto, you know the size of the planet.
“However, to go further – i.e. is it rocky? – involves measuring the mass of the planets and this is much more difficult to do as the stars are too far away for these measurements (which are incredibly difficult) to make.
“So in reality they have no idea what this planet is made of: It could be rock but it could be a small gassy ball or something more exotic maybe.”
Source: BBC