Astronomers catch first sighting of a planet's birth pangs

Alien world forming 450 light years away

Scientists have long postulated that planets are formed by accretion of matter in giant discs of matter around stars, and now an inventive researcher has found a way to spot a far-away world being born.

"This is the first incontrovertible detection of a planet still in the process of forming – a so-called 'protoplanet'," said Kate Follette, a postdoctoral researcher at Stanford and co-lead author on the study in Nature.

The protoplanet has been called "LkCa 15 b" and is located 450 light years away from Earth, meaning that by now it will probably be well formed. It's forming into a gas giant similar to Jupiter and Follette was able to spot it by designing a new sort of imaging instrument with colleagues.

"I was pretty excited as soon as I processed the data, but I wanted to be cautious," said Follette. "I was pretty sure I had found something interesting, but in this field we're always chasing objects that are just at the edge of what we can detect. The really cool thing is that it survived all of our tests to make sure it was real."

As a planet moves through the disc of matter around the host sun it absorbs the matter to add to its bulk. In the case of LkCa 15 b hydrogen gas is accumulating and, as it falls to the protoplanet's surface, it emits a specific wavelength of visible light called "Hydrogen-alpha," or H-alpha.

To get a clear look at the light created in this process the team build an adaptive optics device that both removed the light from LkCa 15 b's sun, and – more importantly – deals with the distorting effect of the Earth's atmosphere on the telescope's view.

"The difference in brightness between a star and a young exoplanet is usually comparable to the difference between a firefly and a lighthouse," she explained.

"It's very hard to isolate the light from the planet when it is so faint and so close to the star from our point of view. But, because we could focus on a special color of light where the planet is glowing very brightly, the signal was significantly stronger than what we normally look for."

Follette said that she was inspired in her career by Carl Sagan's famous 'pale blue dot' image of Earth taken by Voyager and wants to concentrate further research on finding out how other worlds are created in a similar manner as our own Solar System.

"One of the fundamental human questions is whether we're alone or unique," she said. "It's cool to look at Jupiter-like exoplanets like LkCa 15 b, but ultimately we're trying to push the technology to be able to detect Earth-like exoplanets. We'd really like to do that some day for a planet around another star, and this sort of work is moving us in that direction." ®

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