Ever since astronomers started to detect planets beyond our solar system, they've been trying to find another world just like Earth. And few years ago, they announced that they'd found a planet that was the closest match yet -- Kepler-452b. Trouble is, some astronomers now say it's not possible to know for sure that this planet actually exists. From a report: "There's new information that we can now quantify which tells us something that we didn't know before," says Fergal Mullally, who used to be an astronomer on the science team for NASA's Kepler Space Telescope. In 2015, NASA declared that Kepler-452b was the first near-Earth-sized planet orbiting in the "habitable" zone around a star very similar to our sun. The space agency called it Earth's "bigger, older cousin," and scientists were so enthusiastic that one began quoting poetry at a news conference. The original science wasn't shoddy, Mullally says. It's just that, since then, researchers have learned more about the telescope's imperfections.