Neptune-sized moon may be orbiting giant exoplanet

Observations with the Hubble Space Telescope may confirm moon's existence.
By Laurel Kornfeld | Jul 31, 2017
Scientists reviewing exoplanet data taken by NASA's Kepler Space Telescope have found evidence of a Neptune-sized moon orbiting a Jupiter-sized planet about 4,000 light years away.

The moon's existence is not yet confirmed, but the Columbia University-based group of astronomers hope to use the Hubble Space Telescope, which is more powerful than Kepler, to look for it.

Defined as moons orbiting planets that circle stars other than our Sun, exomoons are more difficult to find than exoplanets, and none has yet been confirmed.

Kepler uses the transit method to search for dips in the brightness of stars caused by orbiting planets passing in front of the stars. Moons can be found in a similar manner, by searches for dimming in the reflected light of an exoplanet caused by the transit of an orbiting moon.

David Kipping of Columbia University, who led the research team, reported his team saw three dimmings of the planet as it completed three orbits of its parent star, Kepler-1625.

"After our largest survey to date, we recently detected a strong candidate moon signal in the light curve of Kepler-1625b. The planet exhibits three transits in the Kepler data, in which we detect out-of-transit flux dips consistent with the presence of a large moon," the scientists wrote in a request for time on Hubble on October 29.

Moons are likely to be as common in exoplanet systems as they are in our solar system, said Edward Guinan of Villanova University. Like Europa and Enceladus, exomoons could potentially be habitable for life.

If Hubble observations confirm this moon's existence, it will be the largest moon ever detected. Scientists are already considering several theories as to its formation and history.

The scientists published their findings in the journal Earth and Planetary Astrophysics.

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