To date, thousands of exoplanets — planets that orbit other stars — have been discovered, but no one has discovered an exomoon. But that's a frontier that may soon be crossed, if data collected by a team led by David Kipping of Columbia University can be confirmed, reports Phys.org.

The researchers have found evidence for a Neptune-sized moon orbiting around a Jupiter-sized planet in a star system about 4,000 light-years away. The discovery was made with the Kepler Space Telescope using a method similar to how exoplanets are discovered, by looking at the dimming that occurs as a distant planet passes in front of the star it's orbiting. This time, however, Kipping's team detected an extra wobble in the gloomy dim, the subtle effect of a moon's gravitational tug.

Or at least, that's the best theory to explain the data so far. It's still possible that the dimming was just a statistical aberration, or even the cause of some other object or phenomenon. To confirm that it's a moon, the team has requested time on the Hubble telescope, which is more powerful than Kepler.

That would be a mighty large moon

Exomoons are far more difficult to spot than exoplanets because the objects they orbit don't shine. They're also much smaller than the planets that they orbit. The reason this particular exomoon was potentially detected is that it's such a mammoth moon. All of the moons that orbit the large gas giants in our solar system are rocky worlds, but this exomoon, if it exists, would likely be a gas giant itself.

Such a large moon shouldn't be capable of forming in the same way that moons formed in our solar system, according to our current understanding of solar system formation. So it's possible that this exomoon began its life as a planet before being captured within the gravitational influence of its planet at a later time.

Scientists will know more once the data is confirmed as evidence of an exomoon. Either way, though, there's something strange happening in this star system far, far away. Moon or not, the science of discovery is sure to move forward in exciting new ways.