The star, known as HR 8799, is at the centre of the first planetary system beyond our solar system to be imaged directly, in 2008. The star has at least four gas giants orbiting it. One of them, HR 8799c, is seven times the size of Jupiter that orbits at roughly the same distance Pluto does the sun in our own solar system. The light from the HR 8799c can be distinguished from its star, partly due to its distant orbit.

Having the light from the planet itself means that astronomers can see the planet’s atmosphere in unprecedented detail.

Quinn Konopacky, of the Dunlap Institute for Astronomy and Astrophysics, Toronto, Canada, and her colleagues used one of the Keck telescopes in Hawaii to get the most detailed look at its light yet. They then analysed that to get the chemical composition of the distant planet’s atmosphere. The data came from 5.5 hours of observations, made up of 33 ten minute exposures.

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“We believe this star is the oldest known in the universe with a well determined age,” says Howard Bond of Pennsylvania State University in University Park, who announced the finding 10 January at a meeting of the American Astronomical Society in Long Beach, California.

The venerable star, dubbed HD 140283, lies at a comparatively short distance of 186 light years from our Solar System and has been studied by astronomers for more than a century. Researchers have long known that the object consists almost entirely of hydrogen and helium, a hallmark of having formed early in the history of the universe, before successive generations of stars had a chance to forge heavier elements. But no one knew exactly how old it was.

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