Washington: Astronomers for the first time have deciphered the three-dimensional structure of the atmosphere of a planet beyond our solar system, revealing three layers like a wedding cake on a ferociously hot gas planet that orbits close to a star bigger and hotter than our sun.
The researchers peered through the atmosphere of WASP-121b, an exoplanet also called Tylos, by combining all four telescope units of the European Southern Observatory’s Chile-based Very Large Telescope, discerning a stratification of layers with different chemical compositions and intense winds.
An artist’s impression of the three different layers of the atmosphere on WASP-121b, according to the European Southern Observatory (ESO).Credit: ESO
Until now, researchers have been able to determine the atmospheric chemical composition for some planets outside our solar system – hence their categorisation as exoplanets – but without mapping the vertical structure or how the chemical elements were distributed.
WASP-121b is an “ultra-hot Jupiter”, a class of large gas planets that orbit close to their host star, making them extremely hot. Its atmosphere is mainly composed of hydrogen and helium, like that of Jupiter, our solar system’s largest planet. But WASP-121b’s atmosphere is not like anything ever seen before.
The researchers differentiated three layers by looking for the presence of specific elements. WASP-121b’s bottom layer was characterised by the presence of iron – a metal in gaseous form because of the incredible heat of the atmosphere. Winds move gas from the planet’s eternal hot side to its cooler side.
The middle layer was characterised by the presence of sodium, with a jet stream blowing circularly around the planet at about 70,000 km/h – stronger than any winds in our solar system. The upper layer was characterised based on its hydrogen, with some of this layer being lost into space.
“This structure has never been observed before and defies current predictions as to how atmospheres should behave,” said astronomer Julia Victoria Seidel of the European Southern Observatory and the Lagrange Laboratory at the Observatoire de la Côte d’Azur in France, lead author of the study published this week in the journal Nature.
The researchers also detected titanium in gaseous form in WASP-121b’s atmosphere. On Earth, neither iron nor titanium exist in the atmosphere because they are solid metal owing to our planet’s lower temperatures, relative to WASP-121b. Earth does have a sodium layer in the upper atmosphere.
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