Measuring the wind speed on a brown dwarf

Strong winds blow high in the atmosphere of the brown dwarf 2MASS J1047+21, according to a new study, which presents a simple method to deduce the windspeed in other brown dwarf atmospheres, too. By monitoring the brown dwarf’s infrared and radio emissions, the researchers were able to derive the distant world’s powerful winds – which whip eastward at an average of 660 meters per second, or roughly 2,400 kilometers per hour. The results demonstrate a technique that could be used to characterize atmospheres of exoplanets. Brown dwarfs – bodies with masses between large planets and small stars – share many of the same rotational and atmospheric characteristics as gas giant planets. For gas giants within the Solar System like Jupiter, it’s easy to observe the latitudinal wind patterns that dominate their atmospheres. The speed of those winds can be derived by comparing the movement of clouds in Jupiter’s atmosphere to the radio emissions caused by the rotation of the planet’s interior. Now, Katelyn Allers and colleagues show how this approach can be adapted to measure the winds on gas giants and brown dwarfs far outside our Solar System. Allers et al. observed 2MASS J1047+21, a nearby brown dwarf, and determined its rotational periods at infrared (rotation of the atmosphere) and radio (rotation of the interior) wavelengths. The difference between these measurements allowed the authors to derive the brown dwarf’s average wind speed and direction – about 660 meters per second in an west-east direction. “Our method for determining the wind speed can in principle also be applied to exoplanets,” say the authors, “which have similar rotation rates and periodic variability to brown dwarfs.”

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