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Strange, newly-discovered exoplanet defies planetary formation theories

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Lisa Winter

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180 Strange, newly-discovered exoplanet defies planetary formation theories

Located about 300 light years away in the Crux constellation, HD 106906 b orbits its white main-sequence star. This exoplanet is known as a Super Jupiter, as its mass is 11 times greater than Jupiter. Because of its incredibly large size and the tremendous distance away from the host star, HD 106906 b challenges many current theories about planetary and star formation. This information comes from lead author Vanessa Bailey of the University of Arizona and the results have been accepted for publication in the Astrophysical Journal Letters.

HD 106906 b is about 650 AU away from the star, which is about 20 times the distance from the sun to Neptune. According to current planetary theories, when stars are born, dust and debris swirl around the newborn star in a disk-like shape. As the particles begin to bump into one another, they coalesce and become larger and larger, kind of like a big, dusty snowball. Eventually, the dustball gets so big, it takes on planetary characteristics. This theory also states that there just shouldn’t enough material to form a planet as massive as HD 106906 b at such a great distance. Nevertheless, there it is.


Bailey et al. does propose that this planet could be a failed star. While the host star was forming, it is possible that HD 106906 b just couldn’t accumulate enough material to ignite into a star, which would have made the system a binary star system. This is also problematic, as there is too much of a difference in mass ratio. In typical binary systems, the mass ratio of the two stars maxes out at 10 to 1. In this case, it is closer to 100 to 1.

If it doesn’t form like a planet or a star, how the heck did it get there? Nobody is really quite sure yet. The planet itself is only about 13 million years old (quite the baby compared to our 4.5 billion year old Earth). It is also much cooler than its host star, which temperatures reaching  2,700 F (1,500 C). Astronomers were also able to detect remnants of the dusty disk that spurred formation of the star and planets.

Further study will examine the debris disk as well as analyze the planet’s orbit in order to better understand this mysterious giant planet that, by current knowledge, shouldn’t even exist.


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