By John Wenz
Some astronomers are questioning the existence of what might be the most Earth-like planet yet found outside the solar system, based on a reexamination of archival data.
Kepler 452 b was discovered by NASA’s Kepler space telescope and announced in 2015. At the time it seemed like everything astronomers had hoped for in an Earth analogue: slightly larger and more massive than our planet, and in a habitable 385-day orbit around a star remarkably similar to our sun.
But at about 1,000 light-years away, Kepler 452 b is far too faint for easy follow-up studies. Its apparent existence is based solely on data gathered during Kepler’s primary mission, which ran from 2009 to 2013 before being cut short by equipment malfunctions. During this period the spacecraft stared continuously at a single patch of sky, waiting for any of the stars there to almost imperceptibly dim from the shadows of planets passing across their faces. Such “transits” are how Kepler found the vast majority of its planets; but many things besides planets can cause stars to slightly dim, leading to far more false alarms than discoveries of new worlds. For any candidate planet to be confirmed as genuine, it would have to be observed transiting at least three times. Due to its long orbital period, Kepler 452 b barely met that minimal criterion before the telescope’s primary mission ended—but a host of other, more technical tests convinced the Kepler team the planet had a 99 percent chance of being real.
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