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A Newly Discovered Planet, in its Explosive Infancy

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Astronomical artist Ron Miller creates scientifically accurate images of faraway worlds. In a continuing series for io9, he shares with us another image he's created of a newly formed planet that will one day be bigger than any world in our solar system.


The youngest planet yet discovered has been found orbiting within the disk of dust and gas surrounding the star Lk Ca 15. The planet is more than just young: it may still be in the process of formation. Estimated at being only 50,000 to 100,000 years old, Lk Ca 15b is probably still accumulating mass as it gathers material from the disk within which it orbits.

Astronomers have long believed that our solar system formed from the vast disk of dust and gas that surrounded the Sun shortly after its birth. This dust and gas was, in fact, the debris left over from the formation of our star (and for this reason these disks are called "debris disks"). This idea got a considerable boost from the discovery of stars surrounded by exactly the sort of dust disks the theory described. The first such disk was found in 1984, circling the star Vega. Eventually, nearly a thousand debris disks have been discovered. Many of these appear to contain planets, further confirming the theory that they are planetary maternity wards.


Lk Ca 15b, however, is the first planet anyone has observed that is still in the process of formation. Indeed, the planet's star itself is only 2 million years old—-a mere baby compared to our 4.6 billion-year-old Sun.

The discovery was made by Adam Kraus, of the University of Hawaii's Institute for Astronomy, and his colleague, Michael Ireland of Macquarie University and the Australian Astronomical Observatory. They used the Keck Observatory telescopes on Mauna Kea. The telescope's deformable mirror combined with a new filtering technique called "aperture mask interferometry" enabled the astronomers to resolve the faint disk—-and eventually the planet itself. "In the past, you couldn't measure this kind of phenomenon," said Kraus, "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."

Although still in its infancy, Lk Ca 15b is expected to grow up into a hefty adult, perhaps as large as six Jupiters.


Lk Ca 15b orbits far from its parent star, nearly as far as Uranus orbits from the Sun. From this distance Lk Ca 15 would be dazzling point of light, partially hidden by the glowing inner disk of dust that surrounds it. The distant background sky may not be dark. Instead, the gigantic outer disk may glow faintly in the starlight. The planet itself is busily accreting like mad, slowly growing ever larger as it consumes the dust, gas and asteroids that also occupy the gap in the disk, like a hungry whale cruising through a bed of krill. And the larger the planet grows, the greater its mass becomes. As its gravity increases, it collects ever more raw material. It's already become a Jupiter-sized world. In a few thousand years it will eventually dwarf the largest planet in our solar system.


The discovery image of LkCa 15b. At the left, the gap in the large, outer ring is visible. The hole has a radius about 55 times the distance from the Earth to the Sun. A much smaller, flatter ring surrounds the central star. The planet LkCa 15b orbits within this gap. On the right is detailed view of the central part of the gap. The star indicates the position of LkCa 15 (which has been blocked out to remove its glare). Credit: Kraus & Ireland 2011