Using NASA’s Hubble and Kepler space telescopes, astronomers have uncovered tantalizing evidence of what could be the first discovery of a moon orbiting a planet outside our solar system.
This moon candidate, which is 8,000 light-years from Earth in the Cygnus constellation, orbits a gas-giant planet that, in turn, orbits a star called Kepler-1625. Researchers caution that the moon hypothesis is tentative and must be confirmed by follow-up Hubble observations.
“This intriguing finding shows how NASA’s missions work together to uncover incredible mysteries in our cosmos,” said Thomas Zurbuchen, associate administrator of NASA’s Science Mission Directorate at Headquarters, Washington. “If confirmed, this finding could completely shake up our understanding of how moons are formed and what they can be made of.”
Since moons outside our solar system – known as exomoons – cannot be imaged directly, their presence is inferred when they pass in front of a star, momentarily dimming its light. Such an event is called a transit, and has been used to detect many of the exoplanets cataloged to date.
However, exomoons are harder to detect than exoplanets because they are smaller than their companion planet, and so their transit signal is weaker when plotted on a light curve that measures the duration of the planet crossing and the amount of momentary dimming. Exomoons also shift position with each transit because the moon is orbiting the planet.
In search of exomoons, Alex Teachey and David Kipping, astronomers at Columbia University in New York, analyzed data from 284 Kepler-discovered planets that were in comparatively wide orbits, longer than 30 days, around their host star. The researchers found one instance in planet Kepler-1625b, of a transit signature with intriguing anomalies, suggesting the presence of a moon.
“We saw little deviations and wobbles in the light curve that caught our attention,” Kipping said.