Strong hints have been found of a possible exomoon candidate orbiting a gas giant planet over 4,000 light years away in the constellation of Cygnus the Swan. Should the moon be confirmed later this year by the Hubble Space Telescope, it will be the first moon ever discovered around a planet beyond our Solar System.
The potential discovery has come from the Hunt for Exomoons with Kepler collaboration, which is led by David Kipping of Columbia University in New York. The project uses observations collected by NASA’s Kepler Space Telescope, which watches for dips in starlight as planets cross, or ‘transit’, the face of their host stars and block some of the light.
The idea behind hunting for exomoons is that natural satellites should also cause a dip in the starlight, either just before or just after their parent planets transit. However, given the size of moons compared to their planets, the dip in light caused by an exomoon should be small and hard to discern, even for Kepler.
To even the odds, Kipping’s team stacked together multiple ‘light curves’ (graphs showing how a star’s light output changes over time while a planet is transiting it) for each of the 284 planets they were studying, looking for recurring dips that could be attributed to exomoons. They only found one strong candidate, accompanying the planet Kepler-1625b.
At present Kipping’s team, which includes his Columbia colleague Alex Teachey and citizen scientist Allan Schmidt, are remaining cautious about the potential discovery. The signal of the possible exomoon was seen during three consecutive transits by Kepler, but that’s not sufficient to conclusively confirm the moon exists. The next transit is set to take place in October 2017 and the team have already acquired time on the Hubble Space Telescope to observe the planet and, hopefully, confirm that the moon exists.
If it does exist then it is an exceptionally strange moon quite unlike anything in our Solar System….