Many exoplanets are observed or inferred around distant stars, but astronomers report finding the first exomoon, a smaller body orbiting an exoplanet. It is, mind you, an enormous moon.
We present new observations of a candidate exomoon associated with Kepler-1625b using the Hubble Space Telescope to validate or refute the moon's presence. We find evidence in favor of the moon hypothesis, based on timing deviations and a flux decrement from the star consistent with a large transiting exomoon. Self-consistent photodynamical modeling suggests that the planet is likely several Jupiter masses, while the exomoon has a mass and radius similar to Neptune. Since our inference is dominated by a single but highly precise Hubble epoch, we advocate for future monitoring of the system to check model predictions and confirm repetition of the moon-like signal.
The BBC warns that the authors remain tentative about the exomoon's status. This isn't the first exomoon to be reported, only to be exposed as a boring old exoplanet upon closer inspection.
"We've tried our best to rule out other possibilities such as spacecraft anomalies, other planets in the system or stellar activity, but we're unable to find any other single hypothesis which can explain all of the data we have," said Dr Kipping, from Columbia University in New York.
Sadly, it's unlikely that the exomoon would have an exomoonmoon.
Illo: Beschizza / NASA shots of Jupiter and Neptune