An orange speck that a telescope snapped 500 light-years away in space has been confirmed as the first planet to be directly seen around another star. Astronomers caught their image of the distant world two years ago in a photo of a star like our own Sun in the constellation of Scorpius.
However, they could not be certain that the dot in the same picture was related to it or just in the same line of sight. Adding to the mystery was that it seemed further from the star than they might have expected.
But close observations since have shown that the dot is indeed a planet in the star’s own solar system, it was revealed today. It is only eight times more massive than Jupiter and in an orbit more than 300 times further from the star than we are from the Sun.
What the planet does not have is a name. Astronomers simply use the unromantic label 1RXS J160929.1-210524 – or 1RXS 1609 for short.
The remarkable image of the alien planet was taken by Canadian astronomers with powerful optical equipment attached to the giant Gemini North Telescope on Hawaii. This removes blurs and distortions introduced by currents in the Earth’s atmosphere to produce sharp images of the universe.
Although detective work detecting wobbles and dips in starlight have led to the discovery of hundreds of planets outside the solar system, none had previously ever been imaged directly around a normal star.
Other worlds have subsequently been discovered using direct imaging, however, including a system of three planets around the star HR 8799 also discovered with Gemini. These lie in orbits much closer to their host star. Last year it was even suggested that a natural phenomenon called gravitational lensing had unmasked a planet in the Andromeda galaxy M31.
Discovery team leader David Lafrenière, of the University of Montreal and Center for Research in Astrophysics of Quebec, said: “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. Our new observations rule out this chance alignment possibility, and thus confirms that the planet and the star are related to each other.”
Astronomers now want to find out why the planet is so far from its star. The reason could be a challenge to conventional ideas about planetary formation or the world might have been ejected from a closer orbit by a violent encounter.
When it was discovered, the team also obtained a spectrum of the planet and found it revealed the presence of water vapour, 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 Lafrenière. The result will be published in an upcoming issue of The Astrophysical Journal.
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