On October 3rd, researches from Columbia University published results from the planet-hunting satellite Kepler that alluded to the possibility of a moon orbiting a planet around a distant star, which, if confirmed, would be the first discovery of a so-called “exomoon” in history. The Kepler spacecraft observes light from distant stars over long periods of time, all while watching for dips in light that would be indicative of a planet passing in front of the star. As of this writing, Kepler has made over two thousand planet discoveries, all while surveying about 0.25% of the sky. These researchers, in analyzing the data from star Kepler-1625, discovered a dip in brightness
during the transit of the planet Kepler-1625b across the face of the star. This dip in brightness could be associated with a moon, although it would be incredibly massive, about the size of the gas giant Neptune. By analyzing this dip, they confirmed that, if real, puts the moon at a close enough distance to the planet to be gravitationally bound to the planet. Unfortunately, this dip in light is within experimental error, so it’s very possible that this is a random anomaly. The data set to the right shows this dip, as observed by Kepler and processed by the researchers. More research is needed to pin this down, but, if confirmed, it would be the only moon discovered outside of our solar system, as well as the largest moon ever discovered.
Sources:
http://advances.sciencemag.org/content/4/10/eaav1784/tab-figures-data