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Giant planet 'caught in act of forming'

Paul Sutherland, Feature writer
Mar 5, 2013, 8:00 UTC

Sen—Astronomers believe that they have spotted for the first time a planet in the act of forming from a disc of dust and gas circling a nearby star.

The remarkable observation of a world like Jupiter in the debris around a young star, made with the European Southern Observatory's Very Large Telescope, must still be confirmed.

But if the preliminary results stack up, the image of the young world will be a huge gift to researchers studying theories about how planets form in an embryonic solar system.

The find was made by an international team led by Swiss astronomer Sascha Quanz when he studied the disc of dust and gas surrounding a star labelled HD 100546. This star is relatively close in our galaxy, at a distance of 335 light-years, lying in the southern constellation of Musca, the fly.

The observations intrigued Quanz's team because there appeared to be a blob within the gas and dust that they have identified as a potential gas giant planet.

It revealed itself thanks to an instrument on the VLT called NaCo - Nasmyth Adaptive Optics System/Near-Infrared Imager and Spectrograph - which overcomes the blurring effects of the Earth's atmosphere to produce pin-sharp images. These images, taken at near-infrared wavelengths to picture the heat from the dust, while blotting out the brilliant light from the star itself, were combined with pioneering data analysis techniques.

Dr Quanz, of the Institute for Astronomy in Zurich, said: “So far, planet formation has mostly been a topic tackled by computer simulations. If our discovery is indeed a forming planet, then for the first time scientists will be able to study the planet formation process and the interaction of a forming planet and its natal environment empirically at a very early stage.”

One puzzle if the planet is real is that it orbits the star in the outer regions of its solar system, about 70 times further out than the Earth is from the Sun. This would put it at an equivalent distance to the dwarf planets Eris or Makemake in the Kuiper Belt of our Solar System.

Astronomers will be interested to discover if it has been was born in that outer zone or whether it began to form further in towards its home star before migrating outwards. They will need to rule out the unlikely possibility that it might be a a more distant object that is being viewed through the dust and gas.

ESO VLT image of a candidate protoplanet in the disc of gas and dust around the young star HD100546

This image from ESO’s Very Large Telescope shows the bright candidate protoplanet in the disc of debris around the masked out star HD 100546. Credit: ESO

Previous studies of HD 100546 had suggested that a giant planet orbits it about six times the distance of the Earth from the Sun, though this was not directly imaged.

Another planet has previously been imaged in a dusty disc surrounding an older star much closer to home called Fomalhaut in the southern constellation of Piscis Austrinus. The planet, pictured by the Hubble space telescope in 2008 and known as Fomalhaut b, was confirmed to exist last year after earlier suggestions that it might just be a clump within the dusty debris orbiting the star.

Also last year, the high-altitude ALMA telescope array in Chile provided valuable new information about the nature of the dust disc around Fomalhaut and the planets that help shape it.

Current theory about the formation of planetary systems suggests that giant planets grow by capturing some of the gas and dust left over after a star is born. The astronomers believe that structural features observed in the disc of dust around HD 100546 support their view that its newly imaged planet is real. Furthermore, the protoplanet's surroundings appear to be warmer than elsewhere in the disc as would be expected if it is really a new-forming world.

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An imaginary flight through the disc of gas and dust around HD 100546 towards the possible new planet. Credit: ESO/L. Calçada