About 8,000 light-years away, a giant planet circles an aging star, marching once around its sun in a single Earth-year. But that planet, called Kepler 1625b, might not be traveling completely alone. From a report: Scientists now suspect the planet’s skies are filled by an orbiting mega-moon, a stunningly large world the size of Neptune that may be the first moon spotted outside our solar system. Early hints of its existence surfaced in July 2017, when scientists tentatively announced that they’d found some evidence of an orbital companion for Kepler 1625b. But it wasn’t until the Hubble Space Telescope aimed its eye at the faraway star a year ago that scientists were able to gather enough data to build the case for the so-called exomoon’s presence. Now, the two scientists behind the discovery are hoping for independent confirmation of their finding to really shore up the extraordinary claim. “I’m confident that we’ve done a thorough job vetting this thing, but I also anticipate there will be things other folks come up with that we might not have considered,” says Columbia University’s Alex Teachey, who reports the purported alien moon this week in the journal Science Advances. “Whether those other ideas are fatal to the moon hypothesis or not, that remains to be seen.” For now, MIT’s Sara Seager says she’s reserving judgment. “Exomoons are one of the key items remaining on exoplanet researchers’ wish list,” Seager says. “It’s exciting to see the hunt for the first exomoon continue … and with what would be a shockingly large moon, about the size and mass of Neptune.”
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