Astronomers believe they may have found a second supermoon 5,500 light years away which is orbiting a planet the size of Jupiter.
Researchers spotted the giant exomoon candidate orbiting the planet Kepler 1708b, a world 5,500 light years from Earth, in the direction of the Cygna and Lyra constellations.
The team involved in the research is led by David Kipping and his Cool Worlds Lab at Columbia University, which reported the first exomoon candidate in 2017.
The new exomoon is about a third smaller than the Neptune-sized moon that Mr Kipping and his colleagues previously found orbiting a similar Jupiter-sized planet, Kepler 1625b.
If the sighting is confirmed, it could mean exomoons are as common in the universe as exoplanets, and that the moons are a feature of planetary systems.
But the team’s initial sighting of an exomoon is yet to be confirmed, so it could take years before the second exomoon is established.
Observations from other space telescopes are needed to verify the discovery.
“Astronomers have found more than 10,000 exoplanet candidates so far, but exomoons are far more challenging,” said Mr Kipping, who has spent the last decade hunting for exomoons.
“They are terra incognita.”
In the current study, the researchers looked at the sample of the coldest gas giant planets captured by Nasa’s planet-hunting spacecraft, Kepler.
After scanning 70 planets in depth, they found just one candidate, Kepler 1708b, with a moon-like signal.
Mr Kipping said both of the exomoons are likely to be made of gas that piled up under the gravitational pull caused by their enormous size.
He added that if there are other moons out there, they will be harder to spot as they are likely to be smaller.
“The first detections in any survey will generally be the weirdos,” he said. “The big ones that are simply easiest to detect with our limited sensitivity.”
Should the exomoons be confirmed, they may have the potential to reveal how and where life may have emerged in the universe.
Other astronomers have mixed views about the findings.
Eric Agol, an astronomy professor at the University of Washington, said he is doubtful this latest signal will turn out to be real, stating it could be a “fluctuation in the data, either due to the star or instrumental noise”.
Michael Hippke, an independent astronomer in Germany, said the candidate is “intriguing”.
The study has been published in the peer-reviewed journal Nature Astronomy.
In a separate study, scientists have said a “slushy” ocean of magma could be responsible for the composition of the crust of the Earth’s moon.
Researchers from the University of Cambridge and the Ecole normale superieure de Lyon said the composition could be the result of crystallisation.
It is thought the moon formed when two protoplanets collided and the larger became the Earth while the smaller became the moon.
As a result of the crash, the moon was very hot and crystals, which were inside the liquid magma, solidified over hundreds of millions of years.
Samples collected by Apollo 11 astronauts from the lunar highlands contain light rocks called anorthosites, which formed in the early days of the moon.
They are similar to anorthosites which were formed through the crystallisation of magma on Earth.
Chloe Michaut, from Ecole normale superieure de Lyon, said: “Since the Apollo era, it has been thought that the lunar crust was formed by light anorthite crystals floating at the surface of the liquid magma ocean, with heavier crystals solidifying at the ocean floor.
“This ‘flotation’ model explains how the lunar highlands may have formed.”
The peer-reviewed study has been reported in the Geophysical Review Letters journal.