Have scientists found a massive ‘exomoon’?
Astronomers say they have spotted the first known moon outside our solar system, about 8,000 light-years from Earth. To date, scientists have found more than 3,500 exoplanets—worlds that orbit stars other than the sun—but not a single exomoon. In a bid to rectify that, researchers at Columbia University examined 284 known exoplanets and identified one that might be likely to host a moon. They then directed the Hubble Space Telescope at the planet’s star and watched for two dips in its brightness: one caused by the exoplanet crossing the face of the star, the other by a moon doing the same. Sure enough, 3½ hours after the planet—known as Kepler 1625b—transited across its parent star, the starlight dipped again. The astronomers calculated that the moon is roughly the size of Neptune or Uranus, far larger than any satellite in our own system, and that its host planet is as big as Jupiter. While they acknowledge that further research is needed to confirm their findings, the scientists remain convinced that they’ve discovered an exomoon. “We’ve tried our best to rule out other possibilities such as spacecraft anomalies, other planets in the system, or stellar activity,” co-author David Kipping tells BBC.com. “But we’re unable to find any other single hypothesis which can explain all of the data we have.” ■