Link: Large Exomoon Likely Orbits a Faraway World

[steorra]

It seems like we've found a moon orbiting an extrasolar planet. The moon is approximately Neptune-sized and the planet is approximately Jupiter-sized (which could cover a large range of masses, because once things get about as massive as Saturn they mostly get denser rather than bigger when you add more mass, until they hit star size.)

Large Exomoon Likely Orbits a Faraway World

Teachey and Kipping found that two aspects of the transit data from Hubble were consistent with their exomoon hypothesis. First, the planet transited the star 1.25 hours earlier than expected on the basis of the orbital period measured by Kepler. “That is indicative of something gravitationally tugging on the planet” during this particular transit, Kipping explained.
[...]
Second, the Hubble observations of the host star’s brightness showed two dips in brightness instead of just the one from the planet. “The location, shape, and depth of this event appear consistent with a Neptune-sized moon [also] transiting in front of the star,” Kipping said. The team also saw this secondary dip in the star’s light in some of the Kepler transits.

I wonder if they'll be able to infer enough information about the exomoon's orbit to work out anything about the masses of the planet and moon. I'm guessing likely not, but it is impressive how much information astronomers are able to squeeze out of seemingly tiny amounts of data, so maybe.