Brown dwarfs — like the one illustrated here – are more massive and hotter than planets but lack the mass required to become sizzling stars. Their atmospheres can be similar to Jupiter’s, with wind-driven, planet-size clouds. (NASA/JPL-Caltech)
Results from two very different papers in recent weeks have brought home one of the more challenging and intriguing aspects of large exoplanet hunting: that some exoplanets the mass of Jupiter and above share characteristics with small, cool stars. And as a result, telling the two apart can sometimes be a challenge.
This conclusion does not come from new discoveries per se and has been a subject of some debate for a while. But that borderland is becoming ever more tangled as discoveries show it to be ever more populated.
The first paper in The Astrophysical Journal described the first large and long-lasting “spot” on a star, a small and relatively cool star (or perhaps “failed star”) called an L dwarf. The feature was similar enough in size and apparent type that it was presented as a Jupiter-like giant red spot. Our solar system’s red spot is pretty well understood and the one on star W1906+40 certainly is not. But the parallels are nonetheless thought-provoking.
“To my mind, there are important similarities between what we found and the red spot on Jupiter,” said astronomer John Gizis of the University of Delaware, Newark. “Both are fundamentally the result of clouds, of winds and temperature changes that create huge dust clouds. The Jupiter storm has been going for four hundred years and this one, well we know with Hubble and Spitzer that it been there for two years, but it’s probably more.”
A far cry from 400 years, but the other similar storms and spots identified have been on brown dwarfs — failed stars that start hot and burn out over a relatively short time. Gizis said some large storms have been detected on them but that they’re gone in a few days.
The dust and wind storm on the L dwarf W1906+40 rotates around the cool star every nine hours and is large enough to hold three Earths. L-dwarfs mark the boundary between real stars and “failed stars.” . Most known L dwarfs are brown dwarfs, also known as “failed stars” because they never sustain atomic fusion, but the most massive L dwarfs can fuse hydrogen atoms and generate energy like our sun.
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