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HubbleSite Small Companion to Brown Dwarf Challenges Simple Definition


Space Telescope Science

As our telescopes grow more powerful, astronomers are uncovering objects that defy conventional wisdom. This latest example is the discovery of a planet-like object circling a brown dwarf. It's the right size for a planet, estimated to be 5-10 times the mass of Jupiter. There has been a lot of discussion in the context of the Pluto debate over how small an object can be and still be called a planet. This new observation addresses the question at the other end of the size spectrum: How small can an object be and still be a brown dwarf rather than a planet? This new companion is within the range of masses observed for planets around stars – less than 15 Jupiter masses. But should it be called a planet? The answer is strongly connected to the mechanism by which the companion most likely formed. What's even more puzzling is that the object formed in just 1 million years, a very short time to make a planet according to conventional theory.

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