Astronomers say they've made the first-ever direct observations of a planet in the course of being born and have photographed the cosmic birth.
Using a large telescope in Arizona, they've captured images of a giant gas exoplanet coming into existence in the disk of dust and gas surrounding a young star known as LkCA 15 around 450 light-years away from Earth, they report.
"It's exciting, because it's the first time that we've been able to image forming planets directly," says Stephanie Sallum at the University of Arizona.
"It gives us a system to follow up in the future, in depth, to really understand the details of how planets form," says Sallum, lead author of a paper on the discovery appearing in the journal Nature.
Previously, planetary formation could only be inferred from gaps in the rings of dust and gas around distant stars, assumed to have been cleared by growing planets.
Just such a gap was detected around LkCA 15, leading to speculation the gravity of an infant planet had cleared the material along its orbit around the star.
New observations have established the existence of an exoplanet, LkCA 15b, and astronomers have imaged it directly by looking for hydrogen-alpha photons, a particular kind of light emitted as superheated hydrogen at 17,500 degrees Fahrenheit is pulled into a newly-forming planet.
"We're seeing sources [of protons] in the clearing," Sallum says. "This is the first time that we've been able to connect a forming planet to a gap in a protoplanetary disk."
Other observations suggest two other planets, LkCA 15c and LkCA 15d, also exist in the gap, she adds.
"You have your star, and then there's this gap as you move out from the star. In the images, you see a few points of light in that gap," she explains. "Those would be the planet candidates."
The exoplanet LkCA 15b is around 16 times farther away from its star than our Earth is from our sun, the researchers say.
There is one thing that's puzzling about the discovery, the astronomers admit; since computer models and current theories suggest it takes at least a few millions years for a planet to form, how has LkCA 15b managed to come into being around a star that is just two million years old?
"The researchers' discovery provides stringent constraints on planet-formation theories," writes Princeton University's Zhaohuan Zhu in an article accompanying the published study in Nature.
The new discovery could point the way to discovering more newly-forming planets, he says.
"Such an understanding of the young planet population will shed light on the decades-old problem of planet formation, and reveal how young planetary systems can evolve into older ones such as our solar system, billions of years after they were born," he suggests.
