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takyon writes:

Hubble finds compelling evidence for a moon outside the Solar System

Using the NASA/ESA Hubble Space Telescope and older data from the Kepler Space Telescope two astronomers have found the first compelling evidence for a moon outside our own Solar System. The data indicate an exomoon the size of Neptune, in a stellar system 8000 light-years from Earth. The new results are presented in the journal Science Advances.

[...] In 2017 NASA's Kepler Space Telescope detected hints of an exomoon orbiting the planet Kepler-1625b. Now, two scientists from Columbia University in New York (USA) have used the incomparable capabilities of the NASA/ESA Hubble Space Telescope to study the star Kepler-1625, 8000 light-years away, and its planet in more detail. The new observations made with Hubble show compelling evidence for a large exomoon orbiting the only known planet of Kepler-1625. If confirmed, this would be the first discovery of a moon outside our Solar System.

The candidate moon, with the designation Kepler-1625b-i, is unusual because of its large size; it is comparable in diameter to the planet Neptune. Such gargantuan moons are unknown in our own Solar System.

Other sources put Kepler-1625 at around 4,000 light years away.

Discoveries like this are why we could use as many identical better-than-Hubble space telescopes as we can build and launch.

Also at Sky & Telescope, Cosmos Magazine, The Verge, Axios, NPR, CNN.

Evidence for a large exomoon orbiting Kepler-1625b (open, DOI: 10.1126/sciadv.aav1784) (DX)

Previously: First Exo-Moon Discovered?
First Known Exomoon May Have Been Detected: Kepler 1625b i

Original Submission

takyon writes:

The first suspected exomoon may remain hidden for another decade

A good exomoon is hard to find. Proving that the first purported moon around an exoplanet actually exists could take up to a decade, its discoverers say.

"We're running into some difficult problems in terms of confirming the presence of this thing," said astronomer Alex Teachey of Columbia University at a meeting of the American Astronomical Society on January 10.

[...] That uncertainty is partly because the purported moon seems to be about the size of Neptune, much larger than moon formation theories predict. And the researchers can't rule out that the evidence of the moon isn't actually evidence of a second planet. "We're trying to be very careful about not calling this a discovery, that we've got this beyond a shadow of a doubt," Teachey said.

[...] Ground-based telescopes are trying to confirm if the object is a moon or a second planet based on the object's gravitational tugs on the known planet. That's a much slower process than looking for dips in light from exoplanets and exomoons passing in front of their stars, which is what the Hubble and Kepler data reveal, and could take five to 10 years, Teachey says.

Headline News: Object Not Found.

Previously: First Exo-Moon Discovered?
First Known Exomoon May Have Been Detected: Kepler 1625b i
New Evidence Supports Existence of Neptune-Sized Exomoon Orbiting Kepler-1625b

Original Submission

takyon writes:

Astronomers may have found a second Neptune-size exomoon hidden in the retired Kepler space telescope's data

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 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. 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.

Journal Reference:
David Kipping, Steve Bryson, Chris Burke, et al. An exomoon survey of 70 cool giant exoplanets and the new candidate Kepler-1708 b-i [open], Nature Astronomy (DOI: 10.1038/s41550-021-01539-1)

Yet another observation to add onto JWST's schedule.

Also at Scientific American.

Previously: First Exo-Moon Discovered?
First Known Exomoon May Have Been Detected: Kepler 1625b i
New Evidence Supports Existence of Neptune-Sized Exomoon Orbiting Kepler-1625b
Exomoon Confirmation Remains Elusive

Original Submission