Mysterious Giant Planet Orbiting Distant Sun-Like Star

An international team of astronomers, led by a University of Arizona graduate student, has discovered the most distantly orbiting planet found to date around a single, sun-like star. It is the first exoplanet — a planet outside of our solar system.

Weighing more than 10 times Jupiter’s mass and orbiting its star at 650 times the average Earth-Sun distance, the planet HD 106906 b is unlike anything in our own Solar System.

It’s only13 million years old and at 2,700 Fahrenheit (about 1,500 degrees Celsius), the planet is much cooler than its host star, it emits most of its energy as infrared rather than visible light.

20131208-110347.jpg
This is an artist’s conception of a young planet in a distant orbit around its host star. The star still harbors a debris disk, remnant material from star and planet formation, interior to the planet’s orbit (similar to the HD106906 system). (Image courtesy NASA/JPL-Caltech)

Theoretically, HD 106906 shouldn’t be where it is and therefore, its discovery challenges accepted theories about planet formation.

“This system is especially fascinating because no model of either planet or star formation fully explains what we see,” said Vanessa Bailey, who led the research. Bailey is a fifth-year graduate student in the UA’s Department of Astronomy.

Astronomers have proposed several alternative hypotheses including formation like a mini binary star system.

“A binary star system can be formed when two adjacent clumps of gas collapse more or less independently to form stars, and these stars are close enough to each other to exert a mutual gravitation attraction and bind them together in an orbit,” Bailey explained.

“It is possible that in the case of the HD 106906 system the star and planet collapsed independently from clumps of gas, but for some reason the planet’s progenitor clump was starved for material and never grew large enough to ignite and become a star.”

This system is also of particular interest because researchers can still detect the remnant “debris disk” of material left over from planet and star formation.

“Systems like this one, where we have additional information about the environment in which the planet resides, have the potential to help us disentangle the various formation models,” Bailey added. “Future observations of the planet’s orbital motion and the primary star’s debris disk may help answer that question.”

(Original text: Message To Eagle)

Addendum: text of the original paper

HD 106906 b: A planetary-mass companion outside a massive debris disk

Vanessa Bailey, Tiffany Meshkat, Megan Reiter, Katie Morzinski, Jared Males, Kate Y. L. Su, Philip M. Hinz, Matthew Kenworthy, Daniel Stark, Eric Mamajek, Runa Briguglio, Laird M. Close, Katherine B. Follette, Alfio Puglisi, Timothy Rodigas, Alycia J. Weinberger, Marco Xompero
(Submitted on 4 Dec 2013)
We report the discovery of a planetary-mass companion, HD 106906 b, with the new Magellan Adaptive Optics (MagAO) + Clio2 system. The companion is detected with Clio2 in three bands: J, KS, and L′, and lies at a projected separation of 7.1” (650 AU). It is confirmed to be comoving with its 13±2 Myr-old F5 host using Hubble Space Telescope/Advanced Camera for Surveys astrometry over a time baseline of 8.3 yr. DUSTY and COND evolutionary models predict the companion’s luminosity corresponds to a mass of 11±2MJup, making it one of the most widely separated planetary-mass companions known. We classify its Magellan/Folded-Port InfraRed Echellette J/H/K spectrum as L2.5±1; the triangular H-band morphology suggests an intermediate surface gravity. HD 106906 A, a pre-main-sequence Lower Centaurus Crux member, was initially targeted because it hosts a massive debris disk detected via infrared excess emission in unresolved Spitzer imaging and spectroscopy. The disk emission is best fit by a single component at 95 K, corresponding to an inner edge of 15-20 AU and an outer edge of up to 120 AU. If the companion is on an eccentric (e>0.65) orbit, it could be interacting with the outer edge of the disk. Close-in, planet-like formation followed by scattering to the current location would likely disrupt the disk and is disfavored. Furthermore, we find no additional companions, though we could detect similar-mass objects at projected separations >35 AU. In situ formation in a binary-star-like process is more probable, although the companion-to-primary mass ratio, at <1%, is unusually small.
Comments: 7 pages, 3 figures, accepted to ApJL
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)

Find full text at: Cornell University Library

Image credit: Penn State Science

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