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Astronomers spot hint of first EXOMOON, possibly

Passing planetary body provides fleeting glimpse of something special

NASA Lunar Reconnaissance Orbiter image of the Moon

Thanks to the work of the Kepler space telescope and Earth-bound observations, we have now caught sight of nearly 2,000 exoplanets: planetary bodies orbiting distant stars. But now astronomers think they've caught the first sighting of an exomoon orbiting one of these distant planets.

Planetary moons are relatively common in our Solar System; Earth has one, Mars has two, and Jupiter has 67 of the things that we know about so far. But while the existence of a moon outside our Solar System is thought highly likely, it has always been a matter of conjecture rather than hard science.

The suspected exomoon sighting comes from telescopes in Australasia run by the Japan-New Zealand-American Microlensing Observations in Astrophysics (MOA) partnership and the Probing Lensing Anomalies NETwork (PLANET) programs, and the finding was published in the Astrophysical Journal.

"We present the first microlensing candidate for a free-floating exoplanet-exomoon system, MOA-2011-BLG-262, with a primary lens mass of 4 Jupiter masses hosting a sub-Earth mass moon," the paper reads.

"The data are well fit by this exomoon model, but an alternate star + planet model fits the data almost as well. Nevertheless, these results indicate the potential of microlensing to detect exomoons, albeit ones that are different from the giant planet moons in our solar system."

The team used a technique known as gravitational lensing to make its discovery, whereby a large body passes in front of a target star and its gravitational force bends and focuses the received light, giving much greater detail of both the observational target and the middleman providing the lensing.

Based on the readings the team has received, the middleman object has a tiny orbiting body, one-2,000th of its mass. This could either be a distant, slow-moving small star circled by a planet about 18 times as big as Earth, or a fast-moving planet relatively closer to Earth that's three or four times larger than Jupiter, with a moon significantly smaller than our planet.

"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," said Wes Traub, the chief scientist for NASA's Exoplanet Exploration Program office at NASA's Jet Propulsion Laboratory.

The problem is that the chance for further checking is now gone. The two objects have passed each other and vanished – insofar as we can view them from Earth's vantage point – but the team hopes that with more number-crunching and sky time the confirmation of exomoons will come. ®

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