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2018-10-03. First moon outside the solar system could be as big as Neptune.

posted Oct 6, 2018, 5:32 AM by Alan D. GOULD
By Joshua Sokol, Science Magazine. [https://www.sciencemag.org/news/2018/10/first-moon-outside-solar-system-could-be-big-neptune] For GSS A Changing Cosmos chapter 8. Excerpt: With help from the Hubble Space Telescope, astronomers say they have found compelling evidence for the first known moon outside the solar system. ...this first reported “exomoon” is also strange: a Neptune-size megamoon, some 8000 light-years away, that looms over a giant planet, twice as large in the sky as Earth’s moon. ...Most theoretical models of planet formation struggle to produce such a hefty satellite. However, searches are biased toward the largest moons that might be out there, because bigger things are easier to detect. ...The first hints for the exomoon came from archival data from the Kepler probe, a NASA planet-hunting spacecraft, which looks for dips in brightness caused by unseen planets transiting in front of their suns. Alex Teachey and David Kipping, both of Columbia University, found that three dips, attributed to the planet Kepler-1625b, might actually be caused by a planet and a moon. ...They hoped Hubble, trained on another transit in October 2017, would clinch the case. ...the team stands by its decision to publish its qualified probably-maybe discovery. “Science can’t operate by teams such as ourselves refusing to publish our results and hiding behind closed doors,” Kipping says in an online outreach video posted concurrently with the paper. “If refuted, then we have lost nothing, and the search goes on.”... See also NASA Release, Scientific American article Astronomers Tiptoe Closer to Confirming First Exomoon, and AGU/Eos article (with artist renderings by Dan Durda), Large Exomoon Likely Orbits a Faraway World.