Clouds on Earth are made of water, but on some planets they consist of chemicals such as ammonia and ammonium hydrosulfide. Other planets may have sand clouds, the family of rock-forming minerals that make up more than 90 percent of Earth’s crust.
How do these clouds of tiny dust grains form?
A new NASA study may hold the answers, according to a July 7 press release from the space agency.
How can sand clouds form?
The research deciphers the temperature range at which sand clouds can form in the atmosphere of a distant planet. The researchers reached their conclusions using data that NASA’s now-retired Spitzer Space Telescope collected from brown dwarfs, a category of celestial objects between planets and stars.
“Understanding the atmospheres of brown dwarfs and planets where silicate clouds can form can help us understand what we might see in the atmosphere of a planet that is closer in size and temperature to Earth,” said Stanimir Metchev, professor of exoplanetary studies. at Western University in London, from Ontario, Canada.
Clouds, no matter what they are made of, develop in the same basic way. The ingredient is heated until it vaporizes. It is then trapped and cooled until it condenses. Chemicals such as water, salt, ammonia and sulfur can form clouds.
So can silicate, but this only happens on extremely hot worlds (such as brown dwarfs) because the rock vaporizes at an extremely high temperature, he writes Interesting Engineering.
At what temperatures do such clouds form?
To truly understand cloud formation on brown dwarfs, astronomers collected more than 100 edge detections and grouped them by temperature. They noted that they all fell within the predicted temperature range for where silicate clouds should form: between about 1,900 degrees Fahrenheit (about 1,000 degrees Celsius) and 3,100 F (1,700 C).
“We had to dig deep into the Spitzer data to find these brown dwarfs where there were hints of silicate clouds, and we really didn’t know what we were going to find,” said Genaro Suárez, a postdoctoral researcher at Western University in Canada and lead author of the new study.
“We were very surprised at how strong the conclusion was once we had the right data for analysis,” Suárez added.
The right temperature
The researchers concluded that the temperature must be just right for these clouds to form. In atmospheres hotter than the upper limit of the identified range, the silicates became vapors. On the other hand, a temperature below the lower limit produced clouds that turned into rain or sank lower in the atmosphere.
The study is published in the Monthly Notices of the Royal Astronomical Society.