July 9, 2022 7:15am
Western University researchers are gaining a new understanding of planetary atmospheres that could one day help to determine whether another planet could host life similar to Earth.
Using archived data from NASA’s now retired Spitzer telescope, researchers examined how clouds of small dust grains, known as silicates, form on brown dwarfs – celestial bodies that fall in between planets and stars.
“Understanding the atmospheres of brown dwarfs or hot 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 study co-author Stanimir Metchev, Canada Research Chair in Extrasolar Planets at Western University.
While brown dwarfs form like stars, they aren’t massive enough to kickstart fusion, but they do have atmospheres almost indistinguishable from those on gas-dominated planets, such as Jupiter, so they can be used as an analog for the other, researchers have indicated.
Metchev and Western Science post-doctoral researcher Genaro Suárez gathered more than 100 marginal detections of silicate clouds on brown dwarfs that were observed by Spitzer during the first six years of its mission. They then grouped them by the temperature of the brown dwarf. All of the silicate clouds fell within the predicted temperature range for formation at between roughly 1,000 C and 1,700 C. This effectively revealed the previously unknown temperature range, a definitive trait, at which silicate clouds can form and be visible by telescope.
“We had to dig through the Spitzer data to find these brown dwarfs where there was some indication of silicate clouds, and we really didn’t know what we would find,” said Suárez. “We were very surprised at how strong the conclusion was once we had the right data to analyze.”
In atmospheres charting hotter than the top end of the range identified in the study, silicates remain a vapour. Below the bottom end, the clouds will turn into rain or sink lower in the atmosphere, where the temperature is higher.
The findings have led Metchev and Suárez to believe silicate clouds exist deep in Jupiter’s atmosphere, where the temperature is much higher than it is at the top. They can’t rise higher because at lower temperatures the silicates would solidify and cease to be in cloud form.
“If the top of the atmosphere were thousands of degrees hotter, the planet’s ammonia and ammonium hydrosulfide clouds would vaporize and the silicate clouds could potentially rise to the top,” said Metchev.
Overall the finding provides significant data about the composition of gaseous planet atmospheres, which aids in the understanding of the conditions for Earth-like planets around other stars.
“Our understanding of atmospheres in brown dwarf worlds could let us know how particular the Earth atmosphere is and, therefore, whether or not other worlds have conditions to host life as we know it on Earth,” said Suárez.
The study was recently published in the journal Monthly Notices of the Royal Astronomical Society.