When is a planet not a planet? Well, when it’s a brown dwarf, sort of.
Brown dwarfs are failed stars, objects several times the mass of Jupiter that have been unable to start nuclear fusion in their core. As such, they are a bit of a gray area between a gas giant planet and a star.
They are somewhat confusing – highlighted in a recent study published in The Astrophysical Journal Letters led by scientists from the Carnegie Institute for Science in Washington DC.
They found that an object 21 light-years and 13 times the mass of Jupiter away called SIMP J013656.5+093347, or SIMP0136, is more likely to be a planet-like object than a brown dwarf. It had previously been thought to be one of the closest brown dwarfs to Earth.
What’s the difference? Well, brown dwarfs experience short-lived burning of deuterium at their cores, whereas planets do not. The formation of both is also quite different, while brown dwarfs typically create their own light in the red and infrared spectrum, with planets being relatively dim.
Brown dwarfs also cool down and contract a few hundred million years after their formation, so they can be as hot as stars or as cool as planets depending on their age.
That SIMP0136 is a planet is actually quite useful, though. It is thought to be a free-floating planet, or rogue planet, which means it is not attached to a star. Instead, it’s found in a 200-million-year-old group of stars called Carina-Near.
This is good news for planetary astronomers because it is much easier to study the atmospheres of free-floating planets than it is those in orbit around stars. This is because, for the latter, the host star’s light makes it difficult to see the planet.
"The implication that the well-known SIMP0136 is actually more planet-like than we previously thought will help us to better understand the atmospheres of giant planets and how they evolve," said lead author Jonathan Gagné from Carnegie, in a statement.
This also bodes well for studying weather on other worlds, something that’s becoming more and more important as we look for habitable planets. SIMP0136 is almost certainly not habitable, but it can help us study weather patterns on other worlds.
"This newest addition to the very select club of free-floating planetary like objects is particularly remarkable, because we had already detected fast-evolving weather patterns on the surface of SIMP0136, back when we thought it was a brown dwarf," said Étienne Artigau, co-author and leader of the original SIMP0136 discovery, in the statement.
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