The first moon outside our solar system may have been discovered

Astronomers have discovered what could be the first convincing evidence of an exomoon. The possible exomoon revolves around a giant gas planet located 8,000 light-years from Earth. The massive planet itself gravitates around a star called Kepler-1625.

An exomoon is a moon orbiting an exoplanet or planet outside our solar system. Many exoplanets have been discovered over the years, but to date, no one has found solid evidence of a moon orbiting one of these planets. With the help of NASA's Hubble and Kepler telescopes, researchers have gathered enough evidence to prove the existence of the first exoonoon. The exomoon candidate is incredibly tall, comparable to the size of one of the largest planets in our solar system, Neptune.

"This would be the first case of detection of a moon outside our solar system," said David Kipping, an assistant professor of astronomy at Columbia University. "If confirmed by Hubble's subsequent observations, the results could provide essential clues to the development of planetary systems and lead experts to revisit theories of moon formation around planets."

Unlike the moons of our solar system, the exomoons can not be imaged directly. As they are too far away and vanished, their presence is deduced with a method called transit. When an exomoon passes in front of a planet, it plunges momentarily in the light reflected by this one. These diving events suggest the presence of an object around a planet. Many exoplanets have also been detected using the same technique.

"I think about 75% of people think it's a moon," said Sarah Ballard, an astronomer at the Massachusetts Institute of Technology in Cambridge. "It sums up my skepticism, my confusion and my hope."

The researchers first noticed the existence of this exomoon last year while studying data from the Kepler Space Telescope. When they analyzed data from 284 planets discovered by Kepler, they found a case, in Kepler 1625b, that had intriguing anomalies. Thanks to the new and better observations of the Hubble Space Telescope, researchers are now much more certain that the object is an exomoon.

"A companion moon is the simplest and most natural explanation for the second trough of the light curve and the synchronization deviation between orbit," Kipping said. "It was certainly a shocking moment to see this Hubble light curve. My heart started beating a little faster as I continued to look at this signature. But we knew that our job was to keep a cool head and to assume that it was wrong, by testing every imaginable means by which the data could deceive us. "