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Saturday, February 20, 2016

Exoplanet LkCa 15b

As I was researching astronomy education projects pertaining to exoplanets, (my interest has been growing on the subject lately) I stumbled upon an interesting article on the web about an alien planet announced back in November of 2015. The alien planet, called LkCa 15 b, orbits a star 450 light-years away and appears to be on its way to growing into a world similar to Jupiter.

LkCa 15 b is a candidate protoplanetary object in orbit around LkCa 15, a star in the Taurus-Auriga Star-Forming Region. The object was discovered by direct imaging techniques using the Keck II telescope in 2011 by Adam Kraus and Michael Ireland. A 2015 study of observations from the Magellan Telescope and the Large Binocular Telescope argued that the planet is forming through accretion. It is the first of its kind to be seen in the process of active accretion.

The artist's illustration shows how planets could form in a transition disc around a star similar to LkCa 15 b. Credit: NASA/JPL - Caltech
The artist's illustration shows how planets could form in
a transition disc around a star similar to LkCa 15 b.
Credit: NASA/JPL - Caltech.

"This is the first incontrovertible detection of a planet still in the process of forming--a so-called 'protoplanet'," commented Dr. Kate Follette in a November 18, 2015, Stanford University Press Release. Dr. Follette is a postdoctoral researcher at Stanford in Palo Alto, California, and a co-lead author of the study published in the November 19, 2015, issue of the journal Nature. Dr. Follette's work produced a remarkable digital image of LkCa 15 b glowing in the glaring light of searing-hot hydrogen gas--which is a prediction of planet-formation theories that have now been verified directly by the important observations of Dr. Follette and her co-authors.

The observation was combined in the paper with data that had been provided by Steph Sallum, the co-lead author and doctoral student at the University of Arizona in Tucson, who independently observed the same parent star with a complementary technique. Using the University of Arizona’s Magellan Telescope in Chile, Follette, her adviser at Stanford, Professor Bruce Macintosh, and their co-authors at the University of Arizona were able to hone in on this particular shade of red H-alpha light emanating from LkCa 15 b.

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.

Adaptive optics observations from the Large Binocular Telescope and the Magellan Adaptive Optics System. Credit by: Steph Sallum
Adaptive optics observations from
the Large Binocular Telescope and the
Magellan Adaptive Optics System.
Credit by: Steph Sallum.

The team confirmed the existence of LkCA 15b, imaging it directly in hydrogen-alpha photons, a type of light that's emitted when superheated material accretes onto a newly forming world. (Like newborn stars, newborn planets are surrounded by disks of feeder material.)

In the November 2015 journal Nature, study team members reported that other LBT observations revealed the presence of another newborn planet, LkCA 15c, inside the gap and suggested that a third (LkCA 15d) exists there as well.

"We're seeing sources in the clearing," Sallum said. "This is the first time that we've been able to connect a forming planet to a gap in a protoplanetary disk."

"The researchers' discovery provides stringent constraints on planet formation theories," Zhaohuan Zhu of Princeton University, who was not affiliated with the new study, wrote in an accompanying "News & Views" piece in the same issue of Nature. "For example, such theories now have to explain how a giant planet can form 15-16 AU from its star within 2 million years, and still be growing after this time."

"The new technique demonstrated by Sallum and her team could lead to the discovery of many other newly forming exoplanets, allowing astronomers to learn much more about the distribution of young worlds",  Zhu added.

"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," Zhu wrote.

Sources: Astronomy Now, Wikipedia, Space.com

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