Astronomers using NASA’s James Webb Space Telescope have discovered unusual weather patterns on a giant exoplanet nearly 700 light-years away from Earth.
The planet, called WASP-94A b, appears to develop thick mineral clouds every morning that disappear again by evening.
The findings, published in Science, provide one of the clearest views yet of an exoplanet’s atmosphere and could help scientists better understand how alien weather systems work.
WASP-94A b belongs to a class of planets known as “Hot Jupiters.” These are giant gas planets that orbit extremely close to their stars, making them far hotter than Jupiter in our own solar system.
Because of the intense heat and radiation, their atmospheres behave in unusual ways.
For years, clouds have made it difficult for astronomers to study these planets properly. According to the researchers, observing a cloudy exoplanet is like trying to look through a foggy window. The clouds hide important details about the atmosphere underneath.
Using the advanced instruments aboard the James Webb Space Telescope, scientists found a way to separate the cloudy and clear regions of the planet’s atmosphere.
As WASP-94A b passed in front of its star, the researchers carefully observed different sides of the planet during the transit.
One side represented the planet’s “morning,” where air moves from the cooler nightside into daylight. The opposite side represented the “evening,” where air flows from the hot dayside back into darkness.
The difference between the two sides surprised the researchers.
The morning side was covered with clouds made from magnesium silicate, a mineral commonly found in rocks on Earth. Meanwhile, the evening side had much clearer skies.
Scientists think there are two possible explanations for this strange cloud cycle. One possibility is that strong winds carry the clouds upward on the cooler side of the planet before dragging them deep below the atmosphere on the hotter side, hiding them from view. Another possibility is that the clouds simply evaporate in the extreme heat of the dayside, similar to morning fog disappearing under sunlight on Earth, but at much higher temperatures.
The clear evening skies allowed researchers to study the atmosphere much more accurately than before. Earlier observations using the Hubble Space Telescope suggested the planet contained extremely high amounts of oxygen and carbon, which puzzled scientists because existing theories could not explain such chemistry.
The new Webb observations tell a different story. WASP-94A b appears to contain only about five times more oxygen and carbon than Jupiter, making it much more consistent with current theories of planet formation.
The researchers also examined eight other Hot Jupiter planets and found similar cloud cycles on two more worlds: WASP-39 b and WASP-17 b.
The team now plans to use future James Webb observations to study cloud behavior across many different exoplanets, helping scientists better understand alien climates and the chemistry of distant worlds.
Source: Johns Hopkins University.
