In July 2015, NASA announced Kepler-452 b as the first near-Earth-size planet found in the habitable zone of a Sun-like star. The habitable zone is the range of distances from a star where a planet could, in principle, keep liquid water on its surface. The planet was found with NASA's Kepler space telescope, which watched for the tiny dip in starlight when a planet passes in front of its star, an event called a transit. A team led by Jon Jenkins at NASA's Ames Research Center reported it after searching four years of Kepler data.
On paper, it looks like an older cousin of Earth. Its year lasts about 385 days, and it orbits about 1.05 times as far from its star as Earth is from the Sun. Its star is a G2 star, the same type as the Sun, with a similar temperature, but it is about 6 billion years old, 1.5 billion years older than the Sun. The planet is about 1.6 times Earth's width and receives only about 10 percent more starlight than Earth does. Its mass has never been measured, and the discovery team put the chance that it is rocky at roughly 49 to 62 percent.
The bigger question is whether the planet is there at all. Kepler-452 b was validated statistically: instead of being detected a second way, it was judged real because other explanations for the signal seemed unlikely. In 2018, Fergal Mullally and colleagues argued that this was not enough. Kepler's data contain many false signals produced by the instrument itself, and for weak signals that repeat only once a year or so, those false alarms can outnumber real planets. Kepler caught just four transits of Kepler-452 b. Depending on their assumptions, the team estimated the chance that the signal comes from a real planet at somewhere between 16 and 92 percent, short of the 99 percent normally required. A 2019 study by Christopher Burke and colleagues, using Kepler's final catalogue, agreed that it no longer reaches that bar.
Neither paper says the planet is fake. Both say it should be treated as a candidate until another telescope or technique detects it independently. The NASA Exoplanet Archive still lists Kepler-452 b as confirmed but flags it as controversial, and says it is waiting for stronger evidence either way.
TerraForge's model, working from a mass of 3.29 Earths that is itself estimated from the planet's size, plus its orbit and Sun-like star, simulates a warm water world with a high habitability score. That is one reasonable reading of a planet this size, but the real answer is open twice over: its makeup is unknown, and so, for now, is whether it exists.