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Zones, spots, and planetary-scale waves beating in brown dwarf atmospheres

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Science  18 Aug 2017:
Vol. 357, Issue 6352, pp. 683-687
DOI: 10.1126/science.aam9848

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Beating bands in substellar atmospheres

Brown dwarfs are objects with masses that are between those of large planets and small stars. They share many features with gas giant planets, particularly conditions in their atmospheres. Apai et al. analyzed how the infrared brightness of three brown dwarfs changes over time. Several perplexing features can be explained if bands of clouds rotating within their atmospheres generate beat patterns. Such bands are seen in optical images of Jupiter but best match infrared images of Neptune. The results shed light on the atmospheric physics of brown dwarfs and gas giant planets around the Sun and other stars.

Science, this issue p. 683

Abstract

Brown dwarfs are massive analogs of extrasolar giant planets and may host types of atmospheric circulation not seen in the solar system. We analyzed a long-term Spitzer Space Telescope infrared monitoring campaign of brown dwarfs to constrain cloud cover variations over a total of 192 rotations. The infrared brightness evolution is dominated by beat patterns caused by planetary-scale wave pairs and by a small number of bright spots. The beating waves have similar amplitudes but slightly different apparent periods because of differing velocities or directions. The power spectrum of intermediate-temperature brown dwarfs resembles that of Neptune, indicating the presence of zonal temperature and wind speed variations. Our findings explain three previously puzzling behaviors seen in brown dwarf brightness variations.

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