exo moon exoplanet Kepler-1625b
© Reuters
An artist's impression of the exoplanet Kepler-1625b with the newly discovered exomoon in tow.
Scientists have reported the first ever discovery of a moon orbiting around an 'exoplanet' - a planet that exists outside of the Earth's solar system.

Thousands of exoplanets have previously been found by astronomers, with some suggesting they could possibly support life, but this is the first time scientists have ever found what they believe is a moon orbiting one of them, the newly-released study shows.

"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," said David Kipping, an assistant professor of astronomy at Columbia University, one of the two astronomers who made the discovery.

To make the discovery, the scientists looked at data from 284 exoplanets found by the Kepler Space Telescope and tried to identify anything unusual about their orbits. One of the planets, Kepler 1625b, caught their attention because of "little deviations and wobbles in the light curve," said Kipping.

After watching the planet, the researchers noticed that shortly after it passed in front of its star, there was a second dip of light, indicating that there was "a moon trailing the planet like a dog following its owner on a leash."

Supporting the evidence that this was a moon was the fact that the planet seemed to be passing in front of its star sooner than expected, which could happen due to a moon's gravity, the scientists said.

"An extraterrestrial civilization watching the Earth and Moon transit the Sun would note similar anomalies in the timing of Earth's transit," Kipping explained.

The discovery was first announced reluctantly by the scientists in July 2017 after details were leaked on Twitter. Further observations were then carried out with the Hubble Telescope and are detailed in the study, published in Science Advances.

The astronomers are still waiting for more data to confirm the finding and said that the behavior of the planet could, theoretically, also be caused by another planet in that system - but the prevailing belief is that a moon orbiting the planet is the most convincing explanation.

The planet and the moon are also in the "habitable" zone, which means they are close enough to their star to be given heat but not close enough to kill life instantly. Unfortunately for those excited by the prospect of finding aliens, both are gaseous and are not expected to be harboring any life.