The first exomoon ever found may have been detected by an international team of researchers.
Astronomers are uncertain exactly what they have found. One possibility is a planet about the size of Jupiter, orbited by a moon slightly smaller than the Earth. A star/planet system could also be consistent with the findings.
Microlensing was used to help detect the planetary pairing. This involves waiting until a star or planet seems to pass in front of another star, as seen from the Earth. When occultation occurs, a body passing in front of a background star will cause a magnification of the light seen from the distant stellar body. These events usually last about a month and do not repeat. It is impossible using this method to distinguish between effects created by a star/planet combination and a planet/moon pair.
"If the passing object has a companion - either a planet or moon - it will alter the brightening effect. Once the event is over, it is possible to study the passing object on its own. But the results would still not be able to distinguish between a planet/moon duo and a faint star/planet. Both pairings would be too dim to be seen," Jet Propulsion Laboratory reported on its Photojournal webpage.
Microlensing Observations in Astrophysics (MOA) and the Probing Lensing Anomalies NETwork (PLANET) programs looked for the microlensing effect. The international team that led the study was made up from astronomers representing the United States, Japan and New Zealand. The researchers carried out the study using telescopes located in New Zealand and Tasmania.
"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," Wes Traub, exoplanet chief scientist at the Jet Propulsion Laboratory, said.
Exoplanets, or worlds orbiting stars other than our own Sun, have been the subject of debate for centuries. In ancient Greece, Democritus of Abdera postulated about their existence. In 1600, Giordano Bruno was burned at the stake for suggesting other planets circled around distant stars.
The first exoplanet, 51 Pegasi b, was not discovered until 1995, about 50 light years away from the Earth. This large world orbits close to its home star, which heats the planet. It became the first of a new class of bodies known as hot Jupiters.
This could become the first moon ever detected outside the solar system if the system is found to contain a planet and satellite.
"We won't have a chance to observe the exomoon candidate again. But we can expect more unexpected finds like this," David Bennett of the University of Notre Dame, lead author of the paper announcing the results, told the press.
Observations of a possible exomoon were published in the Astrophysical Journal.