For the first time, astronomers think they've found solid evidence of a moon orbiting a planet outside of our solar system.
And it's a doozy.
The exoplanet, named Kepler-1625b, is 8,000 light-years away and thought to be many times more massive than Jupiter, much larger than any world in our own solar system. The moon orbiting it is about the size of Neptune.
If confirmed, this will be the first time a moon has been found outside of the solar system, according to a new study detailing the finding in the journal Science Advances.
“It is an exciting reminder of how little we really know about distant planetary systems and the great spirit of discovery exoplanetary science embodies," study co-author Alex Teachey said of the discovery in a statement.
Teachey and his co-author David Kipping found the moon — named Kepler-1625b-i — by using the intrepid Hubble Space Telescope.
The research team used the telescope to find small dips in the light of the star orbited by Kepler-1625b and its moon.
At first, 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.
“We saw little deviations and wobbles in the light curve that caught our attention,” Kipping said in the statement.
“It was definitely a shocking moment to see that light curve — my heart started beating a little faster and I just kept looking at that signature."
While it definitely looks likely that the newfound moon is there, researchers will still need to do a bit more work to confirm it.
Image: NASA, ESA
According to the authors of the study, it's possible that the second dip in light could be caused by another planet orbiting the star, but the Kepler Space Telescope didn't find any evidence of a second planet in the system during its observations of the star.
It's also just generally very difficult to find these kinds of objects.
"With exomoons we are stretching the limits of our instrument detection thresholds and precision," astronomer Laura Mayorga, who wasn't involved in the new study, said via email. "The authors are very careful to explain their reasoning behind their conclusions."
In the future, gathering more data about this possible moon and any others could help us put our own solar system in better context as well.
"We need a larger sample of exomoons to place this one and our moons in context," Mayorga said. "Who is the unusual one here?"
Finding moons outside of our solar system could also lead to new discoveries in the hunt for habitable places out in the galaxy.
In our solar system, moons like Europa and Enceladus are thought to be some of the most likely places to find life outside of Earth in our cosmic neighborhood.
"The search for life as we know it starts with water," Mayorga said.
"We still know so little about life in the deep oceans and even in the oceans below the Antarctic ice that Europa and Io are only the beginning of our search for life on moons."