A rare cosmic opportunity allowed astronomers to detect what may be the first signs of an exomoon - a satellite orbiting an as-of-now unknown planet beyond our solar system.

The specific observation, however, were a once-in-a-lifetime opportunity - a chance encounter of objects in our galaxy. But astronomers do expect to come upon similar events in the future.

"We won't have a chance to observe the exomoon candidate again," David Bennett of the University of Notre Dame, said in a statement issued by NASA. "But we can expect more unexpected finds like this."

Bennett is the lead author of a new paper on the findings published in The Astrophysical Journal.

The observation was the result of an astronomy technique known as gravitational microlensing, which takes advantage of chance alignments between stars. When this happens, the foreground star acts as a magnifying glass, intensifying the light emitted from the more distant one. Events like these usually are observable from Earth for about one month.

If the foreground star is orbited by a planet, the lensing effect is altered. But it is not always possible for astronomers to tell exactly what they are looking at. 

Bennett and his colleagues say it is unclear weather the foreground object is a star or a planet, but they do know it the ratio of the object to what appears to be a smaller body orbiting it - about 2,000 to 1. This ratio could mean that the pair could either be a fair star orbited by a planet about 18 times the mass of Earth, or a planet more massive than Jupiter with a moon weighing less than Earth.

But astronomers have no way of telling which of the two scenarios is correct.

"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," said Wes Traub, the chief scientist for NASA's Exoplanet Exploration Program office at NASA's Jet Propulsion Laboratory, Pasadena, Calif. "The researchers' models point to the moon solution, but if you simply look at what scenario is more likely in nature, the star solution wins."

Because the lensing event of the distant bodies is over, it will be nearly impossible for researchers to tell. But they will be able to take what they've learned from this scenario and apply it to any future occurrences of the cosmic phenomenon, which are likely to be observed in the future.