Illustration courtesy Karen L. Teramura, UH IfA
An infrared picture of the planet LkCa 15b, with an icon marking the position of the host star. Image courtesy Kraus and Ireland.
Published October 21, 2011
The newborn gas giant, dubbed LkCa 15b, orbits a sunlike star 450 light-years away in the northern constellation Taurus. (Related: "'First' Picture of Planet Orbiting Sunlike Star Confirmed.")
The planet orbits inside a disk of material around the star that's no more than two million years old. By contrast, astronomers estimate our solar system is 4.6 billion years old.
The big baby planet may be up to six times the mass of Jupiter, according to theory-based calculations, and it appears to orbit 11 times farther from its parent star than Earth does from our sun.
The new picture was made in near-infrared light, but "the planet would probably appear a deep red to our eye, since it's still glowing from the heat of being formed," said Adam Kraus, lead study author and an astronomer at the University of Hawaii.
Separating Light From Light
Kraus and colleagues zeroed in on the young star based on previous observations that showed a conspicuous gap in the star's surrounding debris disk.
Such gaps are thought to be telltale signs that massive, newly formed planets are circling inside the disks—a protoplanet's gravity would clear away a wide swath of gas and dust as it accumulates matter.
"This [gap] is a huge benefit for astronomers who want to find planets—we know a planet is probably there, and we even know approximately where to look," Kraus said.
"We just needed to find a way to distinguish the very faint planet from its very bright parent star."
For this, the team turned to the Keck II 10-meter telescope on the summit of Hawaii's Mauna Kea.
First off, the telescope's deformable mirror was able to correct for distortions in the collected starlight caused by Earth's atmosphere.
The team then used a small mask with several holes placed over the light-collecting mirrors, a method called aperture mask interferometry. This technique allowed the team to block out the light from the host star while capturing the fainter glow of the disk and its embedded planet.
Observing Planet Birth in Action
Kraus and his team plan to continue observing LkCa 15b so they can pin down its temperature and orbital characteristics, such as the shape and orientation of its path around the star.
The team also hopes to expand the search to other stars that have surrounding disks with gaps—and perhaps begin to answer some basic questions about early planet formation.
"We'd been looking for this kind of planet for several years, specifically because we know that observing planet formation in action would tell us a lot about how it actually works," Kraus said.
"My first reaction was that this is finally going to tell us how planets really form!"
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