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First directly imaged
planet confirmed

Posted: 30 June 2010

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First reported in 2008, an exoplanet system discovered orbiting a Sun-like star via direct imaging has been confirmed to host an eight Jupiter-mass planet orbiting its star over 300 times farther than Earth is from our Sun.

The first direct image of 1RXS J160929.1-210524 and its 8 Jupiter-mass companion was presented in September 2008. Follow up observations have now confirmed the discovery. Image: Gemini Observatory.

“Back in 2008 what we knew for sure was that there was this young planetary mass object sitting right next to a young Sun-like star on the sky,” says David Lafreniere, who first reported the observation of the 1RXS J160929.1-210524 system (1RXS 1609 for short) some two years ago. But due to the relative proximity of the planet and star, further observations were required to dismiss the chance that the two objects were just aligned in the sky by chance. “Our new observations rule out this chance alignment possibility, and thus confirms that the planet and the star are related to each other.”

The discovery came thanks to the high resolution adaptive optics set-up at the Gemini Observatory, which enabled Lafreniere's team to take direct images and collect spectra of the system that displayed absorption features due to water vapor, carbon monoxide and molecular hydrogen in the planet’s atmosphere. “In retrospect, this makes our initial data the first spectrum of a confirmed exoplanet ever!” says Lafreniere.

New images of the IRXS 1609 system using the Gemini Near Infrared Imager (NIRI) with the Altair adaptive optics system, at 3.05 microns (left) and 3.8 microns (right). Image: Gemini Observatory/AURA/David Lafrenière (University of Montreal),Ray Jayawardhana (University of Toronto), and Marten van Kerkwijk (University of Toronto).

The confirmation also verified that no other planets with masses between one and eight Jupiter masses orbit closer than 1RXS 1609 does to the sun. Further observations spanning the next few years will help astronomers learn more about the planet's orbit, and the interaction of the planet with the sun. Co-author Marten van Kerkwijk adds that even though the fastest possible orbital period of the planet is over one thousand years, using the instruments at Gemini should yield a precise velocity of the planet relative to its host. In turn, this will let astronomers determine if the planet is on a circular orbit, which would suggest the planet formed far from its star, or if it has a very eccentric orbit, which might suggest it formed closer to its sun but has since been booted out via a close encounter with another planet.

“The unlikely locale of this alien world could be telling us that nature has more than one way of making planets,” says team member Ray Jayawardhana. “Or, it could be hinting at a violent youth when close encounters between newborn planets hurl some siblings out to the hinterlands.”

Despite its distal location the planet boasts temperatures of 1,500 degrees Celsius, yet the host star is around 85 percent the mass of our Sun. The scientists say that the high temperature of the planet can be explained by the young age of the system – just five million years old. A recently formed planet has contracted under self-gravity and will radiate away its heat; in billions of years time it will likely cool to Jupiter-like temperatures of just -110 Celsius.

The full results will be published in an upcoming issue of The Astrophysical Journal.