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Saturn-like rings
circle alien world

Posted: 11 January 2012

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A Saturn-like ring system has been discovered 420 light years away in the constellation of Centaurus by astronomers using the ground-based SuperWASP (Wide Angle Search for Planets) and All Sky Automated Survey (ASAS), but do the rings encompass a planet or a companion star?

A Saturn-like ring system and its host orbit a young star in this artist's illustration. Image: Michael Osadciw/University of Rochester.

The system's four defined rings stretch out tens of millions of kilometres from the central object, and have been dubbed Rochester, Sutherland, Campanas and Tololo after the sites where the eclipsed star was first detected and analysed. The star, known as a rather lengthy 1SWASP J140747.93-394542.6, is similar in mass to our own Sun, but a fraction of its age at just 16 million years.

Usually a star’s light is temporarily and periodically dimmed as a planet passes in front of it, but in this case the team observed an unusually long and deep eclipse with up to 95 percent of the star’s light being dimmed by what the team conclude is a dusty ring system.

“After we ruled out the eclipse being due to a spherical star or a circumstellar disc passing in front of the star, I realized that the only plausible explanation was some sort of dust ring system orbiting a smaller companion – basically a ‘Saturn on steroids,’” says lead scientist Eric Mamajek of Rochester and the Cerro Tololo Inter-American Observatory. “This marks the first time astronomers have detected an extrasolar ring system transiting a Sun-like star, and the first system of discrete, thin, dust rings detected around a very low-mass object outside of our Solar System. But many questions remain about what exactly has been discovered.”

Without yet knowing the mass of the central body, the astronomers are unable to conclude what the ring system is orbiting; it could be a very low-mass star, a brown dwarf, or a gas planet, but they hope to find the answer through follow-up observations over the next two years.

Meanwhile another mystery lies in the rings themselves, in particular, in two pronounced gaps located between rings. In the Saturnian system in our own Solar System, gaps are carved by moons that have enough mass to gravitationally clear a path along their orbits. Mamajek speculates that if the object is a brown dwarf or star then we could be seeing the late stages of planet formation in action. If instead it is a giant planet, then perhaps there is a moon in the making.

The findings were presented today at the 219th meeting of the American Astronomical Society in Austin, Texas, and will be published in an upcoming issue of the Astronomical Journal.