An artist's impression of the gas giant Kepler 1625b with its large moon, Kepler 1625b-i; the pair has a similar mass and radius ratio to the Earth-Moon system but scaled up by a factor of 11.
That's what makes this work so fun, he continued - even if this moon's existence is not confirmed. However, if the Solar system is not something exceptional in the Galaxy, the number of actlon has to exceed the number of exoplanets - and sooner or later we learn to observe them. Such an event is called a transit, and has been used to detect numerous exoplanets cataloged to date.
To spot exoplanets, astronomers look at their host stars, and wait for a planet to pass between the starlight and observers on Earth. Exomoons also shift position with each transit because the moon is orbiting the planet.
In 2017 NASA's Kepler Space Telescope detected hints of an exomoon orbiting the planet Kepler-1625b.
Scientists called it "absolunet" by analogy with the name of earth-like planets orbiting other stars. With his help, they found a second, much smaller hole in the brightness of the star through 3.5 hours after the transit of the planet.
Dr Kipping said this was consistent with "a moon trailing the planet like a dog following its owner on a leash". However, the observation period ended before aktolun has completed its turnover. It's though this occurred as a moon passed across the face of the star blocking its light.
They also noticed that Kepler-1625B was early in starting is transit which is consistent with the wobble of a planet that has an orbiting moon.
Only two planets in our solar system - Mercury and Venus - don't have moons, Kipping said.
In principle this anomaly could be caused by the gravitational pull of a hypothetical second planet in the system.
"If this finding stands up to further observational scrutiny, it represents a major milestone in the field of astronomy", Hodges said. "But we knew our job was to keep a level head and essentially assume it was bogus, testing every conceivable way in which the data could be tricking us". And this is the size that the candidate moon, called Kepler-1625b-i, is. Moons in the solar system are either rocky or icy. Despite its size, the mass of Kepler-1625b-i is estimated to be only 1.5 percent of the mass of its companion planet (Kepler-1625b).
Various attempts have been made previously to confirm or deny that there is a moon outside our solar system.
The host planet and its moon lie within the habitable zone of the star Kepler 1625 where moderate temperatures allow for the existence of liquid water on solid surfaces. But, according to Kipping, neither gaseous object is suitable for life as we know it.
Since researchers first began detecting exoplanets, or worlds orbiting stars other than our Sun, in the early 1990s, we've gone on to catalogue nearly 3,800 alien planets, with thousands more sightings waiting for confirmation.