Astronomers believe they have discovered the first known moon beyond our solar system, in orbit around a gigantic planet 8,000 light years away.
The so-called exomoon, which is estimated to be the size of Neptune, would also be the biggest known moon, far exceeding anything known to exist in our own solar system. The team behind the apparent discovery said it needed further confirmation but that they had failed to find any other convincing explanation for their data.
“The first exomoon is obviously an extraordinary claim and it requires extraordinary evidence,” said David Kipping, an astronomer at Columbia University in New York who has spent more than a decade hunting for far-flung moons.
He said the moon’s estimated size was on a scale that had “hardly been anticipated” and “defies easy explanation” based on current theories of moon formation.
Kipping and his colleague Alex Teachey made the discovery after analysing data from nearly 300 distant planets discovered using the Kepler space telescope. The planets are revealed by a momentary dimming of starlight as they pass in front of their host star, in what astronomers call a transit.