It makes sense to think that moons of planets are widespread throughout our galaxy and beyond. But these exomoon – moons beyond our solar system – are difficult to detect. They’re even harder than distant planets. And we know only just over 4,000 exoplanets of the billions of planets that likely orbit stars in our Milky Way galaxy. And yet there’ve been a few possible detections of exomoon.
To find this nugget, the team sorted through a database of more than 4,000 exoplanets detected by NASA’s now-retired Kepler space telescope. Because large planets orbiting far from their parent star are more likely to have moons large enough to be detected, the team focused on a subset of 70 exoplanets.
After further screening, including tossing out exoplanets that don’t have near-circular orbits (which are statistically less likely to host moons), the team identified a strong candidate for an exomoon. It, like its host planet, caused detectable dimming of the parent star’s light when moving across the face of the star.
This month (January 13, 2022), researchers at Columbia University in New York said they’ve tentatively identified another new exomoon candidate. It’s orbiting a distant exoplanet over 5,000 light-years away.
Discovery of the first possible exomoon, dubbed Kepler 1625 b, has faced a lot of skepticism. Both proposed exomoons need to be confirmed by further observations by other instruments, such as the recently launched James Webb Space Telescope.
The researchers published the details of the exomoon candidate, called Kepler-1708 b-i, in a new peer-reviewed paper in the journal Nature Astronomy on January 13, 2022.
But fresh observations will need to wait: The newfound exomoon candidate and its planet won’t pass in front of the parent star again until March 24, 2023, the researchers calculate.
Astronomers have announced the possible detection of an exomoon, or a moon in another stellar system from our own, the second such candidate observation to date.
If the strange signal does turn out to represent an exomoon, the discovery would give scientists a new understanding of not just this stellar system, but of how such systems work across the galaxy more generally.
The new candidate exomoon was found while the researchers were studying 70 cold, gas giant planets. Like Jupiter and Saturn, they orbit far from their stars. At those distances, there is less gravity from the stars to tug at any moons and remove them from their orbits. They only found one signal of a possible exomoon, but it’s a good one. As Kipping noted:
And of course, the next major observatory, NASA’s James Webb Space Telescope, is finally in space with science work scheduled to start this summer.
“I would be convinced if we observed another transit of the planet with JWST and saw an additional dip in the brightness due to the moon,” Kreidberg wrote. “Exomoons push the limits of our detection capability, so it’s worth being really careful.”
Astronomer Michael Hippke in Germany countered that, however, saying: We find an intriguing object, make a prediction, and either confirm the exomoon candidate or rule it out with future observations. I am very excited to see a second exomoon candidate, although it is unfortunate that only two transits have been observed. More data would be very cool.
“Exomoon have great potential to teach us about how planets form in general,” Kreidberg said. “They’re also really cool! There are dozens of moons in our own solar system, so I wouldn’t be surprised if they’re common around other stars too.
At a smaller scale, an exomoon detection would also offer scientists a more detailed portrait of a planetary system.
Both candidate exomoon are larger than any moon in our own solar system, but that’s not surprising, Kipping said. “The first detections in any survey will generally be the weirdos,” he said. “The big ones that are simply easiest to detect with our limited sensitivity.”
In 2020, astronomers discovered what may be no less than six more exomoon orbiting exoplanets ranging from 200 to 3,000 light-years away.
Bottom line: Astronomers announced a new exomoon candidate orbiting an exoplanet about 5,400 light-years from Earth. Detected in data from the Kepler Space Telescope, it is the latest possible exomoon found so far.