Starship Asterisk*

A new study using archival observations by the now-retired Spitzer Space Telescope found a common trait among distant worlds where the exotic clouds form.

Brown dwarfs – celestial objects that fall between stars and planets – are shown in this illustration with a range of temperatures, from hottest (left) to coldest (right). The two in the middle represent those in the right temperature range for clouds made of silicates to form. Credits: NASA/JPL-Caltech

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Most clouds on Earth are made of water, but beyond our planet they come in many chemical varieties. The top of Jupiter’s atmosphere, for example, is blanketed in yellow-hued clouds made of ammonia and ammonium hydrosulfide. And on worlds outside our solar system, there are clouds composed of silicates, the family of rock-forming minerals that make up over 90% of Earth’s crust. But researchers haven’t been able to observe the conditions under which these clouds of small dust grains form.

A new study appearing in the Monthly Notices of the Royal Astronomical Society provides some insight: The research reveals the temperature range at which silicate clouds can form and are visible at the top of a distant planet’s atmosphere. The finding was derived from observations by NASA’s retired Spitzer Space Telescope of brown dwarfs – celestial bodies that fall in between planets and stars – but it fits into a more general understanding of how planetary atmospheres work.

“Understanding the atmospheres of brown dwarfs and planets where silicate clouds can form can also help us understand what we would see in the atmosphere of a planet that’s closer in size and temperature to Earth,” said Stanimir Metchev ...

• Monthly Notices of the RAS 513(4):5701 (July 2022) DOI: 10.1093/mnras/stac1205
• arXiv > astro-ph > arXiv:2205.00168 > 30 Apr 2022