Wednesday, December 18, 2013

Far Out: This Exoplanet Has the Largest Orbit Even Seen, and It's a Giant Mystery

The thermal infrared image that led to HD 106806 b's discovery, and shows just how unfathomably far it is from its star.
It seems like every time astronomers find a new exoplanet, we’re forced to rethink everything we know about planets and how they’re made. The latest to challenge our perceptions of planetary formation is HD 106906 b, which orbits its star further than any other planet we’ve found.

HD 106906 b, discovered by a team of astronomers at the University of Arizona, is 11 times as massive as Jupiter, but its size isn’t the interesting part. What’s fascinating—and surprising—for astronomers is that this massive planet orbits 650 astronomical units (AU) from its Sun-like star. That’s an orbit 650 times the distance from the Earth to the Sun, or roughly 60,450,000,000 miles.

This isn’t something astronomers have seen before. The research describing the find is available on Arxiv, and will soon be published in the Astrophysical Journal Letters. As Vanessa Bailey, the fifth-year graduate student who led the University of Arizona team, said, “no model of either planet or star formation fully explains what we see.”

The leading theories of planetary formation tend to focus on and explain systems like our own solar system. Planets are thought to form from the primordial disk of gas and dust that surrounds a young, still forming star. From that disk, Earth-like planets close to their stars are thought to gradually coalesce from small asteroid-like bodies over time. But this happens far too slowly to explain giant planets forming so far from their parent stars. It’s possible that these distant giants form from a fast, direct collapse of the primordial disk.

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