Scientists have discovered a possible exomoon orbiting and extrasolar planet. While the discovery is a potential game changer, astronomers are still unsure of the real identity of the mysterious find.

Astronomers the world over have been working hard trying to find new planets outside the solar system. To date, over 1,700 exoplanets have already been discovered and catalogued. While finding an extraplanet in the vast expanse of the universe is more difficult than finding the proverbial "needle in a haystack, astronomers say that finding an exomoon is even harder.

The astronomers that made the discovery say that what they found may be a starless gas giant flying through space. Moreover, the Jupiter-like planet could have an exomoon orbiting around it. The other possibility is that the gas giant they found was orbiting a very dim and very small star. The team published its findings in the Astrophysical Journal.

"We won't have a chance to observe the exomoon candidate again," said University of Notre Dame's research professor of Astrophysics and Cosmology David Bennett of the University of Notre Dame. "But we can expect more unexpected finds like this." Bennet is also the paper's lead author.

To find the possible exomoon, scientists from the Probing Lensing Anomalies NETwork (PLANET) and the Microlensing Observations in Astrophysics (MOA) used gravitational lensing. This type of lensing occurs when a massive celestial object passes in front of another object, typically a star. Due to the powerful gravitational fields of the foreground object, light from the background object gets magnified and its trajectory bends around the foreground object in a manner similar to an optical lens.

In the case of the mysterious planet with the possible exomoon, which served as the foreground object in the team's gravitational lensing analysis, there was a small anomaly in the team's calculations. They found that the foreground object should have a smaller companion with a mass of approximately 0.005 percent relative to the larger object.

The lensing system is now referred to as MOA-2011-BLG-262. If the main object is a planet and the distance of the system from Earth is relatively short, it would probably be classified as a "rogue planet," which does not orbit a star. If the object is faraway however, the lensing effect would imply that the system would include a massive star. 

"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 NAA Exoplanet Exploration Office's chief scientist Wes Traub. "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." Traub was not involved in the study.

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