Astronomers from Columbia University have discovered a moon orbiting a gas-giant planet just 8,000 light-years away.
Using NASA's Hubble Space Telescope and Kepler Space Telescope, the scientists - Alex Teachey and David Kipping - reported in apaper published in the journal Science Advances the detection of a candidate exomoon.
A candidate exomoon refers to a moon orbiting planets in other star systems.
This would be the first case of detecting a moon outside our solar system
However, this moon is unusual because of its large size, which is more comparable to the diameter of Neptune. Such large moons do not exist in our own solar system.
"This would be the first case of detecting a moon outside our solar system," said Kipping, assistant professor of astronomy at Columbia.
"If confirmed by follow-up Hubble observations, the finding could provide vital clues about the development of planetary systems and may cause experts to revisit theories of how moons form around planets."
In looking for exomoons, the researchers analysed data from 284 Kepler-discovered planets that were in comparatively wide orbits, with periods greater than 30 days, around their host star. The observations measured the momentary dimming of starlight as a planet passed in front of its star, called a transit. The researchers found one instance, in Kepler 1625b, that had intriguing anomalies.
"We saw little deviations and wobbles in the light curve that caught our attention," Kipping said.
Both bodies, however, are considered to be gaseous and therefore unsuitable for life as we know it
The Kepler results were enough for the team to get 40 hours of time with Hubble to intensively study the planet, obtaining data four times more precise than that of Kepler.
The researchers monitored the planet before and during its 19-hour-long transit across the face of the star. After it ended, Hubble detected a second and much smaller decrease in the star's brightness 3.5 hours later, consistent with "a moon trailing the planet like a dog following its owner on a leash".
"Unfortunately, the scheduled Hubble observations ended before the complete transit of the moon could be measured," Kipping said.
The host planet and its moon lie within the solar mass star's (Kepler 1625) habitable zone, where moderate temperatures should allow for the existence of liquid water on any solid planetary surface. "Both bodies, however, are considered to be gaseous and therefore unsuitable for life as we know it," Kipping added.
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