The first suspected exomoon is coming into focus. Hubble Space Telescope data bolster the case for a Neptune-sized moon orbiting an exoplanet 8,000 light-years from Earth, astronomers report October 3 in Science Advances. If confirmed, the moon would challenge theories of how satellites are born. David Kipping (SN: 10/14/17, p. 22) and Alex Teachey of Columbia University focused Hubble on Kepler 1625 for some 40 hours on October 28 and 29, 2017. The star was known to have a Jupiter-sized planet orbiting every 287 days, thanks to data from the Kepler space telescope, which detects dips in starlight that indicate a planet is transiting in front of a star. Teachey and Kipping had seen signs in the Kepler data of a second dimming, either before or after the planet passed - what would be expected if an exomoon were orbiting the planet (SN: 8/19/17, p. 15). The pair named the possible moon Kepler 1625b i, or "Neptmoon." But more observations were needed to be sure it was really a moon, not another planet or activity on the star.
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