This artist’s impression depicts the exomoon candidate Kepler-1625b-i.

For the first time, astronomers think they’ve found solid evidence of a moon orbiting a planet outside of our solar system.


The object was spotted in data from Nasa’s Kepler spacecraft and later observed using the Hubble telescope. This “exomoon” is not like any in our cosmic neighborhood: it’s the size of Neptune and orbits a planet the size of Jupiter – but with 10 times the mass.

“We’ve tried our best to rule out other possibilities such as spacecraft anomalies, other planets in the system or stellar activity, but we are unable to find any other single hypothesis which can explain all of the data we have,”

– Co-author David Kipping, an astronomer at Columbia University in New York, told reporters earlier this week.

However, he and lead author Alex Teachey, also a Columbia astronomer, stressed that the observations don’t constitute a definitive detection.

“We hope to re-observe the star again in the future to verify or reject the exomoon hypothesis,”

“And if validated, the planet-moon system — a Jupiter with a Neptune-sized moon — would be a remarkable system with unanticipated properties, in many ways echoing the unexpected discovery of hot Jupiters in the early days of planet hunting.”

– Kipping said.

The team of researchers led by Columbia University astronomer Alex Teachey think they discovered a moon orbiting the planet Kepler-1625b, which is located 2.4 kiloparsecs (roughly 8,000 light-years) from our planet and surrounded by the constellation Cygnus.

The researchers monitored a planet Kepler 1625b as it passed in front of its parent star. And during its 19-hour event, known as a transit, it blocked out some of the light coming from the star, which lies at a distance of 8,000 light-years from Earth. The researchers saw the dip in light caused by the planet passing across the face of the star, but not long afterward, they saw a second, smaller dip, likely caused by the moon transiting across the star.



Teachey and co-author David Kipping published their findings in the journal Science Advances on Oct. 3. They say the first exomoon is rather strange because of its larger size, comparable to the diameter of our solar system’s Neptune – it is big – scientists have not discovered any moon that large among the 200 natural satellites observed in our solar system.

To date, astronomers have discovered more than 3,500 exoplanets. The hunt for exomoons – bodies that orbit these distant planets – has proceeded in parallel. But so far, these natural satellites have lingered at the limits of detection with current techniques.