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Dust clouds have been theorized in cool extrasolar atmospheres since the 1990's. They are the favoured mechanism to account for the increasingly red spectra of brown dwarfs at decreasing temperatures, while patchiness in the cloud cover can explain the ubiquitous brightness variability of brown dwarfs. However, dust clouds have also posed a conundrum, where their presumed rapid sedimentation produces a wide variety in observed spectral morphology contained within only a 50-100 K temperature range.
The conundrum is now being resolved through direct spectroscopy with the James Webb Space Telescope, which is sensitive to the 8-11 micron absorption signature of dust (silicate) clouds. Dust absorption is seen to correlate with the spin axis inclination of brown dwarfs: equatorial latitudes appear cloudier and redder than the poles. This is a significant development in the study of brown dwarfs and exoplanets alike. It may explain the wide scatter in their observational properties as a viewing geometry effect, much like the Unified Model for Active Galactic Nuclei (AGN) explains the apparent AGN diversity as a line-of-sight effect.
The availability of accurate spin axis inclinations of brown dwarfs and of very low mass stars has further motivated an efficient search for transiting, potentially habitable Earth-like exoplanets: by focusing on potential host stars viewed from above their equators. A proposed Canadian space mission aims to implement this observational approach. The POET (Photometric Observations of Exoplanet Transits) mission would launch by 2030, and would aim to find the nearest Earth-like planets amenable to atmospheric biosignature detection with James Webb or with the next generation of Extremely Large Telescopes.