LONG BEACH, California – Astronomers have confirmed that a controversial exoplanet called Fomalhaut b actually does exist and have calculated its potential orbit. The results show that the object is even stranger than scientists could have imagined, dubbing it a “rogue planet.”
The uncertainty about this object started in 2008, when scientists released an image taken with NASA’s Hubble space telescope of a tiny dot of light in the debris disk of a young, bright star called Fomalhaut, which is about 25 light-years away in the constellation Piscis Austrinus. At the time, they presented only two data points, showing the exoplanet as it existed in 2004 and 2006. It was a sensational image — the enormous debris disk made the star resemble the “Eye of Sauron” from the Lord of the Rings movies — and was one of the first directly imaged extrasolar planets ever seen.
But follow-up from other researchers failed to find the purported world. The original instrument on Hubble that saw Fomalhaut b broke in 2007 and was never replaced, meaning the team that discovered the exoplanet couldn’t reproduce their results either. When they spotted it in 2010 with another instrument, the object seemed to have drifted too far to the right to be in orbit around the star. This led some astronomers to discount the discovery of Fomalhaut b.
But late in 2012, a few other telescopes managed to snap images of the exoplanet. And now, the original team has presented their own new data. “We have three times as many orbits and there you see it very clearly in 2012,” said astronomer Paul Kalas of the University of California at Berkeley and the SETI Institute, pointing to a new image released today during a press conference here at the American Astronomical Society 2013 meeting.
With their four data points, the original team has been able to calculate several potential orbits for the object. They show the exoplanet moving on a highly eccentric orbit around its parent star, coming in as close at 40 astronomical units (AU) and then swinging out to 350 AU. (An AU is the distance between the Earth and the sun). There is some indication that the planet’s orbit is very inclined relative to the debris disk around Fomalhaut, meaning that the exoplanet doesn’t pass through it, instead moving above and then underneath the dust.
This movement suggests to Kalas and his team that Fomalhaut b is a rogue planet, acting much more like a comet or icy body in our solar system’s Kuiper belt, which generally orbits far from the sun but may sometimes come in closer. The astronomers think the mass of the exoplanet is at least as much as an icy dwarf world, like Sedna in our solar system, but it could be as big as Jupiter. In either case, it’s unlike anything seen in our own system and shows that the architecture of other planetary systems could greatly differ from our own.
Image: NASA, ESA, and Paul Kalas (University of California, Berkeley and SETI Institute). Video: NASA/STSCI