Astronomers have collected compelling evidence for the discovery of what could be an exomoon, a moon outside our solar system.

If the discovery turns out to be true, this would be the first time astronomers find a moon orbiting a planet outside our Solar System.

Data shows that the moon orbits a gas-giant planet 8,000 light-years away.


The latest finding is definitely intriguing. This natural satellite is incredibly large, comparable to the size of the gas giant Neptune in our solar system, which is highly unusual. There’s no sign of such a large moon in our solar system. Astronomers have cataloged around 200 natural satellites orbiting the Sun.

Astronomers call the parent of this exomoon Kepler-1625b which orbits around a star similar to our Sun.

During 40 hours of intensive investigation, using Hubble telescope, researchers obtained data four times more precise than that of Kepler.

However, the parent planet of this exomoon, Kepler-1625b, is several times the mass of Jupiter. This means their mass-ratio is similar to that of Earth and its moon.

The Discovery

The astronomy team from Columbia University made the discovery using two of NASA’s space telescopes. First, by investigating data collected by the Kepler Space Telescope, astronomers noticed a signal from an object. Then, they continued their investigation with the Hubble Space Telescope.

“This would be the first case of detecting a moon outside our solar system,” said Kipping, an assistant professor of astronomy at Columbia. “If confirmed by follow-up Hubble observations, the finding could provide vital clues about the development of planetary systems and may cause experts to revisit theories of how moons form around planets.”

Astronomers used the transit method where they measured the momentary dimming of starlight as a planet passed in front of its star. But this time they saw something intriguing.

“We saw little deviations and wobbles in the light curve that caught our attention,” Kipping said.

Perhaps that wobble could be due to the presence of a second planet, the researchers thought. But Kepler didn’t find any other planets around this star.

“A companion moon is the simplest and most natural explanation for the second dip in the light curve and the orbit-timing deviation,” Teachey said. “It was a shocking moment to see that light curve. My heart started beating a little faster, and I just kept looking at that signature. But we knew our job was to keep a level head, testing every conceivable way in which the data could be tricking us until we were left with no other explanation.”

The reason exomoons are so difficult to find is that they are so small and so their transit signal is weak. But they also shift position with each transit because the moon is orbiting the planet.

However, Kipping also mentioned that the upcoming James Webb Telescope could help us find really tiny moons.

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Thumbnail image: Artist’s impression of the exoplanet Kepler-1625b transiting the star with the candidate exomoon in tow. Credit: Dan Durda