Using NASA’s Hubble and Kepler space telescopes, astronomers have found evidence for what could be a moon orbiting a planet outside our solar system. This would be the first time this phenomenon has been observed.
The moon ‘candidate’, which is 8,000 light-years from Earth in the Cygnus constellation, orbits a gas-giant planet. In turn, the planet orbits a star named Kepler-1625.
Commenting on the potential discovery, Thomas Zurbuchen, associate administrator of NASA’s Science Mission Directorate at NASA Headquarters, Washington, D.C. said, “If confirmed, this finding could completely shake up our understanding of how moons are formed and what they can be made of.”
Moons outside our solar system — or exomoons — cannot be imaged directly. Their presence can only be deduced when they pass in front of a star, causing its light to fluctuate. This is also called a ‘transit’. They are also far harder to detect than exoplanets as they are dwarfed by their companion planet.
It was Alex Teachy and David Kipping, astronomers at Columbia University who discovered a ‘transit signature’ while observing the planet Kepler-1625b. Commenting on the discovery, Kipping said, “We saw little deviations and wobbles in the light curve that caught our attention.”
It was also found that the planet transit occurs over an hour earlier than predicted, which supports the moon hypothesis. This is consistent with the planet and moon orbiting a common center of gravity that would cause the planet to wobble from its predicted location, much the way the Earth wobbles as our Moon orbits it.
It should be noted however, that the planetary wobble could be caused by the gravitational pull of a hypothetical second planet, rather than a moon. So far a second planet has not been detected, yet it is still possible that a second planet exists but is not detectable using the Hubble and Kepler telescopes.
Regardless, Kipping insists that “a companion moon is the simplest and most natural explanation for the second dip in the light curve and the orbit-timing deviation.”
This moon is estimated to be only 1.5 percent the size of its companion planet, which is estimated to be several times the mass of Jupiter. This is a mass-ratio similar to the one between Earth and the Moon. However, in the Earth-Moon system, it was dust leftover after rocky planetary collisions that went on to form the moon. However, Kepler-1625b and its possible satellite are gaseous and not rocky, so the moon candidate may have formed through a different process.