5 février 2015

Des anneaux gigantesques


Saturne, Uranus et Neptune peuvent aller se rhabiller. Ces anneaux-ci sont sont d'une taille vraiment étonnante:

A young exoplanet called J1407b has a gigantic ring system that’s much heavier and about 200 times larger than the rings of Saturn. Astronomers discovered the giant planet or possibly a brown dwarf (that is, a failed star) when it eclipsed a very young sun-like star called J1407. This ring system—the first of its kind to be discovered outside the solar system—has at least 30 rings, each of which measures tens of millions of kilometers in diameter. 

"You could think of it as kind of a super Saturn," University of Rochester’s Eric Mamajek says in a news release. 

(...) Based on the light curve, the diameter of the ring system is nearly 120 million kilometers and contains roughly an Earth's worth of mass in its light-obscuring dust particles. The rings blocked up to 95 percent of J1407’s starlight for days—which means there are lots of satellite-spawning material. The researchers have already found at least one clean gap in the ring structure, and they think it was carved out by the formation of a satellite (or exomoon) with a mass between that of Earth and Mars and an orbital period of about two years around J1407b.

The rings will probably thin out over the next several million years, eventually disappearing as satellites form. Jupiter and Saturn, when they were very young, may have had disks around them that led to the formation of their moons. "However, until we discovered this object in 2012, no one had seen such a ring system,” Mamajek explains. “This is the first snapshot of satellite formation on million-kilometer scales around a substellar object."

J1407b’s orbital period around its star is roughly a decade long, and its mass could be as much as 40 Jupiters. “If we could replace Saturn's rings with the rings around J1407b,” Kenworthy adds, “they would be easily visible at night and be many times larger than the full moon." We’d be able to see them at dusk with our naked eyes and camera phones. Just for fun, here’s how that would look in the skies of Leiden above the Old Observatory:


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