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Astronomers might have spotted one of the first exomoons

We have now confirmed the existence of over 4,000 exoplanets, or planets outside our solar system, which are teaching us about how planets and systems form and could even help us locate other habitable worlds. However, one object that’s harder to spot is an exomoon. Astronomers think it’s very likely that moons exist outside our solar system, but because they are generally so small they are exceedingly hard to identify. However, astronomers from Columbia University believe they may have located evidence of an exomoon.

The potential exomoon, which is very large and is orbiting a Jupiter-sized planet called Kepler 1708b, is located 5,500 light-years away. It is the second candidate exomoon discovered by the same team, headed up by David Kipping. “Astronomers have found more than 10,000 exoplanet candidates so far, but exomoons are far more challenging,” said Kipping in a statement. “They are terra incognita.”

Artist's impression of an exomoon.
The discovery of a second exomoon candidate hints at the possibility that exomoons may be as common as exoplanets. Helena Valenzuela Widerström

Kipping and his team looked at archival data from NASA’s Kepler telescope and honed in on the coldest gas giant planets. They chose to focus on these exoplanets because the equivalent planets in our solar system, Jupiter and Saturn, both have many moons orbiting them.

They searched through data on 70 planets before finding the signal of the one exomoon candidate. Being super-sized meant that this signal stood out, and if further candidates are discovered in the future, they likely won’t be so large. “The first detections in any survey will generally be the weirdos,” Kipping explained. “The big ones that are simply easiest to detect with our limited sensitivity.”

Astronomers will need to collect more data before they can confirm whether the candidate is in fact an exomoon, or whether it’s just an oddity in the data. It’s possible that the signal could be caused by the planet interacting with its star, or noise from the Kepler instrument. So for now, Kippling and his colleagues will continue to search for more evidence about whether this is in fact a moon beyond our solar system.

The research is published in the journal Nature Astronomy.

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