First Exomoon Possibly Glimpsed
By Clara Moskowitz
Exoplanets are almost old hat to astronomers, who by now have found more than 1,000 such worlds beyond the solar system. The next frontier is exomoons—moons orbiting alien planets—which are much smaller, fainter and harder to find. Now astronomers say they may have found an oddball system of a planet and a moon floating free in the galaxy rather than orbiting a star.
The system showed up in a study using micro lensing, which looks for the bending of starlight due to the gravitational pull of an unseen object between a star and Earth. In this case the massive object might well be a planet and a moon. But the signal is not very clear, the researchers acknowledge, and could instead represent a dim star and a lightweight planet. “An alternate star-plus-planet model fits the data almost as well” as the planet-plus-moon explanation, the scientists reported in a paper that was posted this week on the preprint site arXiv. The study has not yet been peer-reviewed.
"I was excited by this paper," says astronomer Jean Schneider of the Paris Observatory, who was not involved in the research. Exomoons have "become fashionable these days," he adds, and are one of his personal "holy grails." Schneider wrote a paper in 1999 on how to detect exomoons using an alternative method, called transiting. (The transit technique looks for the dimming of a star's light caused when a planet or moon passes in front of the star from Earth's perspective).
Now that astronomers know planets are common in the galaxy, exomoons, too, are likely to abound, scientists say. Yet they are exceedingly hard to find, due to their diminutive size and lack of brightness. The authors of the new paper, led by David Bennett of the University of Notre Dame, note that micro lensing is promising because it can detect moons beyond the close-in satellites that transit searches are best equipped to find. Regardless of whether the new system turns out to include a moon, "these results indicate the potential of micro lensing to detect exomoons," the authors wrote.
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http://www.scientificamerican.com/article.cfm?id=exomoon-alien-planet
