On a quest to understand how planets are formed – and ultimately how Earth fits into the cosmic picture – astronomers have uncovered the chemical composition of an exoplanet 850 lightyears away with unprecedented precision.
The new study, published in Nature Astronomy, found that silicon monoxide gas is present in the atmosphere of exoplanet WASP-121b or 'Tylos'. This is the first and only time the gas has been detected in the atmosphere of any planet – including those in our solar system and the exoplanets beyond the solar system.
The research was led by University of Newcastle astronomer Dr Tom Evans-Soma in collaboration with Institutes from across the world1. The team observed Tylos continuously for 40 hours using NASA's James Webb Space Telescope – a $US 10 billion piece of equipment.
Tylos was discovered in 2015 and is one of the thousands of exoplanets, which are planets located beyond our solar system, that has been discovered during the past 30 years.
Dr Evans-Soma said their aim was to learn more about the chemical composition and atmospheric temperatures of Tylos, which is an ultrahot gas giant comparable to Jupiter in our solar system but much hotter.
"For most exoplanet observations, data will be taken for just a few hours at a time. 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," Dr Evans-Soma said.
A pixel tells a thousand words
During the 40-hour observation of Tylos, 3,500 exposures were captured with the telescope - roughly one every minute.
"In these snapshots, we're looking for changes in the brightness of essentially a single pixel to give us clues about the atmospheric conditions of the planet," Dr Evans-Soma said.
"On the planet's dayside, we found water vapor and carbon monoxide, which we were expecting.
"We also detected silicon monoxide, which was a first. But what really surprised us was the detection of methane on the planet's nightside.
"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," Dr Evans-Soma said.
Reaching temperatures over 2,500 degrees Celsius, Tylos is one of the hottest planets that has been discovered.
A planet born in deep freeze and forged in fire
The unexpected findings challenge existing simulations of atmospheric dynamics and offer more clues on how planets are formed.
Dr Evans-Soma said their study revealed that the concentrations of carbon, oxygen, and silicon were higher in the atmosphere of Tylos than in its host star.
"This suggests that when Tylos formed 11 billion years ago it was positioned much further away from its host star, where temperatures were low enough for water to freeze into ice.
"Under these conditions, we'd expect Tylos to accumulate lots of carbon-rich gas from the protoplanetary disk, resulting in a high ratio of carbon-to-oxygen in the final atmosphere, which is what our observations revealed.
"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, which we detected in this study," Dr Evans-Soma said.
An artistic impression shows the stage at which "Tylos" or WASP-121b accumulated most of its gas. Credit: T. Müller (Max Planck Institute for Astronomy)
The bigger picture – life beyond Earth?
This research is part of the overarching quest to understand how our own planetary system originated and evolved over time.
"Of course, one day we hope to answer the age-old question of whether there's life elsewhere in the Universe," Dr Evans-Soma said.
"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."
"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," Dr Evans-Soma said.
The paper 'SiO and a super-stellar C/O ratio in the atmosphere of the giant exoplanet WASP-121b' was published today in Nature Astronomy.
1This study was led by the University of Newcastle (Australia) in collaboration with a team of 18 researchers from Max Planck Institute for Astronomy (Germany), Johns Hopkins University (USA), The Open University (UK), The University of Birmingham (UK), The University of Oxford (UK), Space Telescope Science Institute (USA), NOIRLab (USA), National Institute of Science Education and Research (India), The University of Exeter (UK), NASA Jet Propulsion Laboratory (USA), Flatiron Institute (USA), The University of Illinois at Urbana-Champaign (USA), The University of Columbia (USA), and The University of Arizona (USA).
