Scientists are watching the birth of a planet orbiting a star 450 light years away and say what they learn could answer some of the biggest questions concerning how planets form around other stars.
The alien planet, called LkCa 15 b, appears to be on its way to growing into a world similar to Jupiter.
“This is the first incontrovertible detection of a planet still in the process of forming—a so-called ‘protoplanet’,” says Kate Follette, a postdoctoral researcher at Stanford University and co-lead author on the study that is published in the journal Nature. Follette’s work produced a digital picture of LkCa 15 b glowing in the light of ultra-hot hydrogen gas.
The observation was combined in the paper with data from Steph Sallum, the co-lead author and a graduate student at the University of Arizona, who independently observed the same star with a complementary technique.
The planet is forming in a transition disk, a doughnut-like ring of dust and rocky debris orbiting its parent star, LkCa 15. The central clearings within transition disks are believed to be created by the formation of planets, which sweep up dust and gas from the disk as they orbit the star. Astronomers have long speculated that investigating these gaps could lead to the discovery of protoplanets, but getting a good look at these infant worlds has been challenging.
For the new study, researchers took a new tack, and designed an imaging instrument to look for a characteristic planet formation signature. The process by which a planet grows from a rocky or icy core to a full-fledged gas giant is incredibly energetic. As hydrogen gas falls from the disk onto the core of the protoplanet, it heats up and glows like a fluorescent light bulb, emitting a characteristic wavelength of visible light called “Hydrogen-alpha,” or H-alpha.
Using the University of Arizona’s Magellan Telescope in Chile, researchers were able to home in on this particular shade of red H-alpha light emanating from LkCa 15 b.
“I was pretty excited as soon as I processed the data, but I wanted to be cautious,” says 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.”
Firefly and a Lighthouse
To make the discovery, the scientists processed the images to remove the light from the host star, allowing them to isolate light from the much fainter planet. The protoplanet is very close to its parent star, and if it were much closer or fainter, LkCa 15 would have washed out its light completely.
