The detection of clouds beyond Earth raises many expectations. For example, Venus or Mars have been extensively studied in recent years. However, if there are clouds that are more interesting, they are found outside the solar system. They are mostly clouds of substances that condense at high temperatures, such as silicates, iron or certain salts and sulphides. Water clouds are very rare. Therefore, the fact that a brown dwarf was found with water clouds around it in 2014 is a milestone. A milestone that has now been taken a step further, as it has been discovered that they are variable water clouds.
Clouds that change in density. Thanks to observations made with the James Webb Space Telescope, a team of scientists from the University of Arizona discovered that the clouds around the brown dwarf WISE 0855 change in thickness over time, similar to Earth’s climate. In particular, they become thicker and thinner as the object rotates and show different regions with different cloudiness and temperature. On the other hand, rhythmic signals of carbon monoxide and phosphine were detected. These gases are drawn into the upper atmosphere by convection from the deep, hot layers of the brown dwarf.
Better than photometry. Traditionally, clouds around planets or brown dwarfs have been studied using photometry. This technique allows detecting brightness changes in light coming from objects. But the light is detected as a single band or, at most, several. Therefore, they cannot understand what causes this brightness change. On the other hand, spectrographs like James Webb’s separate light into its different bands according to their wavelength. As a result, they can detect many more specific changes and determine the composition and temperature of the object’s atmosphere, among other parameters.
Therefore, it can be expected that more such clouds will be detected in the future. Of course, it should be noted that WISE 0855 is quite close to Earth, 7.4 light-years away. Additionally, it has a suitable temperature for water vapor to condense and form clouds. It is actually the coldest brown dwarf known. There aren’t many planets or brown dwarfs that are close enough and cool enough to study. Still, now that we have James Webb, WISE 0855 could be no exception.
Why a brown dwarf? Brown dwarfs are objects halfway between a star and a planet. Basically, they are too big to be considered planets, but too small to fuse hydrogen like stars. Nevertheless, they bear some resemblance to Jupiter and gaseous exoplanets.
That is the key. All this understanding is not interesting because it is a unique phenomenon, there is nothing like it outside the boundaries of the solar system. It’s also interesting because, because of this similarity to Jupiter, understanding how clouds form on this brown dwarf could give us information about the atmospheres of gas giant exoplanets. James Webb has begun to study them thoroughly, so this first discovery could be a great thread to pull.
Image |NASA/JPL-Caltech
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