New-found Planet Defies Scientific Theory

Artist’s conception of HD106906b a young planet in a distant orbit around its host star. (NASA)

A newly-discovered  planet outside of our solar system has scientists rethinking how planets form.

The international research team said the new exoplanet, with the registration number HD 106906b,  is not only huge, weighing 11 times Jupiter’s mass, but also orbits its sun from a distance of 650 au’s – astronomical units or 97,238,615,955 km.  In comparison, the distance from the Sun to Pluto at its farthest orbital point – is 7,375,623,552 km.

“This system is especially fascinating because no model of either planet or star formation fully explains what we see,” said Vanessa Bailey, a graduate student at Tucson’s University of Arizona who led the research team.

The location and attributes of this giant exoplanet defy conventional planet formation theories.

It is thought that planets forming within a solar system usually do so at a relatively closer distance to their home stars.  Among other planet formation theories one indicates that there shouldn’t be enough of the primordial material with the mass needed to create a planet the size and weight of HD 106906b at a distance so far from its sun.

HD 106906b is only about 13 million years old.  In comparison, scientists believe Earth was born about 4.5 billion years ago, which makes our planet 350 times older than HD 106906 b.

This is a discovery image of planet HD 106906b in thermal infrared light from MagAO/Clio2, processed to remove the bright light from its host star, HD 106906A. The circle around the star indicates distance from Neptune to our sun. (Vanessa Bailey)

The exoplanet is so young, according to the researchers, that it still glows with the left-over heat from its formation. The planet temperature is about 1,500 degrees Celsius and cooler than its sun, so HD 106906b emits most of its energy within the infrared spectrum rather than visible light.

The team used the new Magellan Adaptive Optics (MagAO) system and the Clio2 thermal infrared camera, which was mounted to the 6.5 meter-diameter Magellan telescope located in Chile’s Atacama Desert.

The MagAO system was developed by University of Arizona scientists to allow Earth-based telescopes take sharper images of the night sky than ever before. (see a related story)  This new optical system can counteract the blurring effects of the atmosphere by floating a very thin curved glass mirror that vibrates a 1,000 times per second  on a magnetic field that is set about 9 meters above the telescope’s primary mirror.

This atmospheric correction system allowed the research team to detect the weak heat emitted from the exoplanet without it being interfered with by the overpowering heat from its much hotter sun.

Scientists have thought that planets like Earth, which are relatively close to their suns,  form when remnant material from a star’s formation–such as dust and gas–gathers together.

But, according to the scientists, that method of planet formation may act too slowly for the giant planets located far from their sun to form.

The Magellan Telescope with MagAO’s Adaptive Secondary Mirror (ASM) mounted at the top looking down on the 6.5m (21 foot) diameter Primary Mirror. (Yuri Beletsky, LCO/Magellan Staff)

Another theory suggests that these giant planets can form as the result of a fast, direct collapse of the primordial disk material. But the team says that in the case of HD 106906b, which is so far from its sun, any disks of planet forming material usually don’t have enough mass to create a planet.

Scientists have also developed and offered other theories including one that speculates how mini-binary star systems are formed.

“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,” said Bailey. “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.”

Bailey and her team have outlined their research and discovery in a paper that will be published in a future issue of The Astrophysical Journal Letters.