Astronomers have found what they say are the first signs of an exomoon, or a moon that orbits a planet outside our solar system.
The researchers, funded by NASA, came across the possible exomoon after an unexpected sighting of an interaction between two objects in our galaxy, the Milky Way. But the interaction will never be seen again, according to a Thursday statement from NASA's Jet Propulsion Laboratory, based at the California Institute of Technology.
"We won't have a chance to observe the exomoon candidate again," David Bennett, lead author of a paper on the findings, said according to the statement.
"But we can expect more unexpected finds like this," Bennett added.
The discovery can open doors to finding other exomoons.
Signs of the exomoon were found during a study conducted by the joint Japan-New Zealand-American Microlensing Observations in Astrophysics and the Probing Lensing Anomalies NETwork programs.
Using telescopes based in New Zealand and Tasmania, astronomers used a technique where stars are studied as one star passes in front of another distant star, called gravitational microlensing.
When this happens, the star closer to Earth, or the foreground star, acts like a "magnifying glass" and makes the distant star brighter, according to the statement.
The researchers were able to detect two objects that were close together, passing in front of a distant star at the same time.
"The ratio of the larger body to its smaller companion is 2,000 to 1," the statement said. "That means the pair could be either a small, faint star circled by a planet about 18 times the mass of Earth- or a planet more massive than Jupiter coupled with a moon weighing less than Earth."
Researchers are unable to definitively say if the objects are a star and planet or a planet and its moon.
"One possibility is for the lensing system to be a planet and its moon, which if true, would be a spectacular discovery of a totally new type of system," Wes Traub, NASA's Exoplanet Exploration Program chief scientist, said in the statement.
