According to NASA, the Kepler and Hubble space telescopes have found evidence of a satellite that is orbiting exoplanet Kepler-1625b. Exoplanets are one of the most exciting discoveries in astronomy – they are worlds outside our solar system, some of which are suspected to be able to support life.
The satellite in question, roughly the size of Neptune, lies around 8,000 light-years away from earth and it might mark the very first time astronomers have found a moon orbiting around an exoplanet.
The new moon is bigger than any of the almost 200 natural satellites that have been found in our own solar system and it has been discovered when the researchers monitored exoplanet Kepler-1625b as it was passing in front of its parent star. The transit blocked some of the light coming in from the star and this dip in brightness was registered as the Kepler-1625b.
But a second one followed, almost like an afterthought. It clearly indicated a moon that was trailing behind the planet.
Even with all this information, the scientists do not yet want to make an exomoon claim officially, not until they will be receiving more data to base their claim on. So, for now, it is just a candidate for the title.
These reservations exist because this would be a first-of-its-kind detection—the first exomoon. Historically, the first exoplanet claims faced great skepticism because there was simply no precedence for them. If many more exomoons are detected in the coming years with similar properties to Kepler-1625b-i, it would hardly be a controversial claim to add one more. Ultimately, Kepler-1625b-i cannot be considered confirmed until it has survived the long scrutiny of many years, observations and community skepticism, and perhaps the detection of similar such objects.
Exomoons are difficult to find because they are very small, so the dip they cause in light is obviously weaker than a planet that is, by comparison, much larger. In addition, because they orbit the planet, their own orbit is also constantly shifting.
One of the main questions to be asked about the exomoon is where it came from. While our own Moon is mostly thought to have formed when a collision shot off some material that has become the rock we see today, that would not be possible with this exomoon because both the moon and the planet it orbits are made up of gas.
Even if it might be strange that a Neptune-sized moon could exist out there, at the same time, nothing in physics says that it can’t. Mysteries, mysteries.