Evrim Yazgin
Cosmos science journalist
Data from NASA’s James Webb Space Telescope in the hands of Australian astronomers has led to the discovery of a unique gas in the atmosphere of exoplanet, WASP-121b.
The exoplanet, also called “Tylos”, is a gas giant, a little bigger than Jupiter, orbiting a star about the same size and mass as our Sun. Tylos is tidally locked to its host star, meaning that the same side of the planet faces the star at all times.
Tylos is about 40 times closer to its star than Earth is to the Sun, making it extremely hot – about 2,500°C, one of the hottest exoplanets so far discovered. Tylos is for that reason known as an “ultra-hot Jupiter”.
Tylos was discovered in 2015. It has been subject to a number of studies which have pointed to the planet’s extreme weather and gemstone rain. Now, astronomers using Webb have observed the planet continuously for 40 hours and come up with a strange new discovery.
The findings are published in Nature Astronomy.
“For most exoplanet observations, data will be taken for just a few hours at a time,” says first author Tom Evans-Soma from Australia’s University of Newcastle. “Our observation was more ambitious than this – we monitored Tylos as it completed a full orbit around its host star. We measured the thermal emission across all phases of the planet’s orbit, which allowed us to probe both the dayside and nightside atmosphere.”
They found a chemical compound never before seen on any exoplanet or any planetary body in our own solar system: silicon monoxide.
Even more surprising was evidence of methane on Tylos’s nightside – the side of the planet which is always facing away from its star.
“Methane has been found in only a handful of exoplanets so far. Usually, it’s only present in atmospheres of lower temperature planets. We’ve never detected methane on a planet as hot as Tylos,” Evans-Soma explains.
Carbon, oxygen, and silicon concentrations on Tylos were higher than in its host star.
“This suggests that, when Tylos formed 1.1 billion years ago, it was positioned much further away from its host star, where temperatures were low enough for water to freeze into ice.
“The silicon enrichment of the atmosphere also suggests that Tylos incorporated a substantial amount of rocky material as it formed – a quantity equivalent to about 30 times the mass of Earth. This rocky material was likely delivered by asteroid-like bodies colliding with the planet and becoming engulfed in the atmosphere.
“When the planet moved closer to its host star, the atmospheric temperature increased so much that this rocky material was vaporised, forming gases such as silicon monoxide,” Evans-Soma says.
Evans-Soma says that such studies bring us a step closer to finding evidence of life on other planets.
“Although Tylos is too hot to support life as we know it, by refining our observational techniques and improving our understanding of these exotic atmospheres, we hope to make steady progress towards characterising more Earth-like planets in the future,” he explains.
“Living organisms produce waste gases that are released into the atmosphere, forming biosignatures. Measuring the chemical composition of planetary atmospheres and searching for these biosignatures is arguably the most promising means of identifying life beyond our solar system.”
