By analyzing the silhouette of an exoplanet passing in front of its parent star 420 light-years away, astronomers have discovered what may be a large gas giant world sporting a ring system. Could it be Saturn's twin?
The star in question is called 1SWASP J140747.93-394542.6 and astronomers spent 54 days in 2007 watching its brightness change in a rather curious way.
Exoplanet observatories have a few methods they can apply to observe worlds orbiting distant stars, but in the case of 1SWASP J140747.93-394542.6 the orbiting exoplanet was spotted as it drifted in front, blocking a portion of the star's light from view.
This in itself isn't unheard of - after all, NASA's Kepler space telescope has spotted hundreds of candidate exoplanets using this "transit method" - but the way in which the starlight dimmed was peculiar.
The as the star's brightness changed over time, its "light curve" exhibited a strange pattern. Rather than smoothly dimming and then brightening as a spherical exoplanet drifted past the star's disk (as would normally be expected), its brightness dramatically fluctuated.
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Using data from the SuperWASP (Wide Angle Search for Planets) project and All Sky Automated Survey (ASAS), University of Rochester astronomer Eric Mamajek and graduate student Mark Pecaut spotted another unusual dimming event in December 2010.
"When I first saw the light curve, I knew we had found a very weird and unique object," said Mamajek. "After we ruled out the eclipse being due to a spherical star or a circumstellar disk 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.'"
As this particular exoplanet passed in front of its parent star, it would appear Mamajek and Pecaut were observing the Saturn-like rings pass in front of the star as well as the world itself. The discrete structures within the exoplanets ring system caused dramatic fluctuations in star brightness as the transit progressed - starlight flickering as it passed through the ring structures. At some points of the ring transit, 95 percent of starlight was blocked by the dust.
"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," said Mamajek, "But many questions remain about what exactly has been discovered."
It's possible that the object in the center of the ring system is either a very low-mass star, brown dwarf, or gas giant planet. To arrive at this answer, they hope to follow up with radial velocity measurements of the star's motion.
As the exoplanet (or, indeed, stellar body) orbits 1SWASP J140747.93-394542.6, it will exert a gravitational "tug" on the star. The amount of wobbling can reveal the mass of the object, thereby giving astronomers an idea as to what the object might be.
So this fascinating ringed object could be an exoplanet or something a little more star-like, but I really do hope it's a "Saturn on steroids."
Source: Univ. of Rochester
Illustration Credit: Michael Osadciw/University of Rochester