Photograph by Peter Michaud, Gemini Observatory
Published June 30, 2010
Two years after making the claim, a team of astronomers says it holds bragging rights to releasing the first ever direct picture of an alien planet orbiting a sunlike star.
Most of the more than 400 known extrasolar planets, or exoplanets, have been found using indirect detection methods, such as looking for changes in starlight as a planet's gravity tugs on its host star, or as the planet passes in front of the star.
Unveiled in September 2008, a picture from the Gemini North telescope in Hawaii shows a direct view of a star system dubbed 1RXS 1609. At the time, astronomers didn't have enough data to say for sure that the bright dot near the star was in fact an orbiting world and not just an object in a chance alignment, as seen from Earth.
Several other teams have made and confirmed direct pictures of exoplanets, including a 2004 picture of the planet Fomalhaut b—also orbiting a sunlike star—which was released a few months after the shot of 1RXS 1609.
Using more observations and new pictures from Gemini, the team studying 1RXS 1609 has now confirmed that their original picture does in fact show a planet circling the young star.
"From the start we suspected that the two were gravitationally bound, but it was just a matter of patiently waiting and watching long enough to see some motion," said team leader David Lafrenière, an exoplanet researcher at the University of Montreal in Canada.
"Now we finally have the data to say that the planet and star are indeed bound and travel together through space at the same direction and speed."
Picture Shows Unusually Far-Out Planet
The new data also helped astronomers refine estimates of the mass and orbital distance of the pictured planet.
After studying the unique properties of light from the system, Lafrenière and colleagues concluded the planet is about eight times more massive than Jupiter, making it a relative lightweight among known exoplanets.
The object orbits roughly 31 billion miles (50 billion kilometers) away from its host star—about 330 times the distance between Earth and the sun. By contrast, the dwarf planet Pluto orbits, on average, about 3.6 billion miles (5.8 billion kilometers) from the sun.
The finding suggests the planet in the 1RXS 1609 system is the smallest known world orbiting at such a vast distance from its stellar host.
It's unclear whether the far-out planet originally formed in its current location or was born much nearer to the star and was later kicked outward by gravitational interactions with a now missing planetary neighbor.
Either way, the extreme separation poses challenges to the current view of solar system formation and evolution, Lafrenière said. (Related: "Planets Found With Crisscross Orbits—A First.")
"This discovery proves that not all systems are similar to our own, with all planets relatively close to their star," Lafrenière said.
"It's exciting to see that there is definitely much more diversity in planets than what we ever thought was out there."
Findings will appear in an upcoming issue of The Astrophysical Journal.
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