Despite an explosion of exoplanet discoveries since the 1990s, astronomers have not confirmed the discovery of a single exomoon. In fact, only around a dozen exomoon candidates have been put forward up to now.
In 2018, David Kipping (Columbia University) and Alex Teachey (now at Academia Sinica, Taiwan) were the first, tentatively reporting [skyandtelescope.org] a possible Neptune-radius moon about 7,800 light-years from Earth: Kepler-1625 b-i. Now, the astronomers and other colleagues have announced the discovery of another exomoon, published January 14th in Nature Astronomy [nature.com]. However, just as before, they urge both caution and the need for further observations.
The putative exomoon, designated Kepler-1708 b-i, was found 5,700 light-years away, orbiting a Jupiter-size planet around a star similar to the Sun. The planet is on a Mars-like orbit, at about 1.6 astronomical units (a.u.). Its moon orbits about 12 planetary radii away, similar to Europa's distance from Jupiter. Unlike Europa, though, Kepler-1708 b-i is huge, about 2.5 times Earth's size. This means the moon would be unlike any satellite in our solar system.
Yet another observation to add onto JWST's schedule.
Also at Scientific American [scientificamerican.com].
Previously: First Exo-Moon Discovered? [soylentnews.org]
First Known Exomoon May Have Been Detected: Kepler 1625b i [soylentnews.org]
New Evidence Supports Existence of Neptune-Sized Exomoon Orbiting Kepler-1625b [soylentnews.org]
Exomoon Confirmation Remains Elusive [soylentnews.org]