To understand the mechanism by which high-temperature exoplanets form silicate clouds (sand clouds), astronomers studied brown dwarfs and found that silicate clouds can only form in a fixed temperature range.
Clouds are common on the earth. Water changes in three states with temperature changes. The cloud-making mechanism is relatively simple. Water exists on the surface as solid ice or liquid water. When the temperature increases, the water evaporates when heated, forming a free-floating gas in the atmosphere, but it condenses into small particles when the temperature cools. Water droplets or ice crystals form clouds. Other planets form different types of clouds due to their temperature and chemical composition. Jupiter, for example, is known for its ammonia-rich clouds.
For a long time, astronomers have predicted that some exoplanets will form silicate clouds. Silicates are the constituents of planetary sand and rocks. Researchers believe that the formation mechanism of silicate clouds is similar to that of water clouds, but the temperature of silicate clouds is higher. high.
In order to understand the mechanism, the researchers analyzed the infrared data of brown dwarfs observed in the early days of NASA’s Spitzer Space Telescope (SST). Brown dwarfs are between stars and planets. The researchers analyzed more than 100 brown dwarfs and grouped them according to temperature. The predicted temperature range at which silicate clouds are found to be suitable for formation is about 1,000-1,700°C (about 1,900-3,100°F). When the temperature is above the projected range, the silicate cloud will evaporate; when the temperature is below the projected range, the silicate cloud will sink from the atmosphere. The research was published in the Monthly Notices of the Royal Astronomical Society.
▲ The three-state changes of the silicate cloud (sand cloud) at different temperatures of the brown dwarf.
Researchers believe that silicate clouds exist deep in Jupiter’s atmosphere. Due to the influence of atmospheric pressure, the temperature in the depths is much higher than the temperature at the top of the clouds, and the silicate clouds cannot rise higher. Because the upper temperature is low, the silicate clouds will condense and sink. Cloud state is not maintained. If the temperature at the top of the Earth’s atmosphere rises by thousands of degrees, the Earth’s ammonia and ammonium hydrosulfide clouds will evaporate, and silicate clouds may form at the top of the atmosphere.
Some exoplanets are between 1,000 and 1,700°C. Based on this study, astronomers believe that such planets may have silicate clouds.
(This article is reproduced with permission from the Taipei Planetarium; image source: NASA)
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