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Kraus Finds Planet in the Process of Forming

Artist's conception of the area near the planet LkCa 15 b.

Artist's conception of the area near the planet LkCa 15 b, by Karen Teramura, IfA.

IfA postdoctoral fellow Adam Kraus and Australian colleague Michael Ireland have taken the first direct image of a planet in the process of forming around its star. What astronomers are calling LkCa 15 b looks like a hot "protoplanet" surrounded by a swath of cooler dust and gas, which is falling into the still-forming planet. Images have revealed that the forming planet sits inside a wide gap between the young parent star and an outer disk of dust.

"LkCa 15 b is the youngest planet ever found, about five times younger than the previous record holder," said Kraus. "This young gas giant is being built out of the dust and gas. In the past, you couldn't measure this kind of phenomenon because it's happening so close to the star. But, for the first time, we've been able to directly measure the planet itself as well as the dusty matter around it."

Kraus and Ireland observed LkCa 15 b with the Keck telescope on Mauna Kea. They combined the power of Keck's adaptive optics with a technique called aperture mask interferometry. Adaptive optics involves the use of a deformable mirror to rapidly correct for atmospheric distortions of starlight. Aperture mask interferometry involves placing a small mask with several holes in the path of the light collected and concentrated by a giant telescope. It allows the astronomers to cancel out the bright light of stars. They can then clearly see disks of dust around stars and the gaps in the dusty layers where protoplanets may be hiding.

"Interferometry has actually been around since the 1800s, but through the use of adaptive optics has only been able to reach nearby young suns for about the last 7 years." said Dr. Ireland. "Since then we've been trying to push the technique to its limits using the biggest telescopes in the world, especially Keck."

"LkCa 15 was only our second target, and we immediately knew we were seeing something new," said Kraus. "We could see a faint point source near the star, so thinking it might be a Jupiter-like planet we went back a year later to get more data."

In further investigations at varying wavelengths, the astronomers were intrigued to discover that the phenomenon was more complex than a single companion object.

"We realized we had uncovered a super Jupiter-sized gas planet, but that we could also measure the dust and gas surrounding it. We'd found a planet at its very beginning," said Kraus.

Kraus and Ireland plan to continue their observations of LkCa 15 and other nearby young stars in their efforts to construct a clearer picture of how planets and solar systems form. "Different theories of planet formation make very different predictions," Kraus explained. By continuing their study of young planets, they hope to make a significant contribution to figuring out how planets actually form.