The discovery of a daily cloud cycle of a distant 'hot Jupiter' has given researchers a unique insight into the planet's evolution and make-up.
A team of international scientists has discovered that sand clouds form every morning – but clear up by nightfall - on the gas giant WASP-94A b, found in constellation nearly 700 light years away from Earth.
The research, which uses data from the James Webb Space Telescope (JWST), is among the first to detect cloud cycles on a Hot Jupiter exoplanet.
By isolating the clouds, researchers can more accurately measure the planet's atmosphere and provide one of the clearest pictures to date of the planet's composition, a significant advance in planetary science.
The results are published today in the journal Science.
"I've been looking at exoplanets for 20 years, and general cloudiness has been a thorn in our side. We've known for quite a while that clouds are pervasive on Hot Jupiter planets, which is annoying because it's like trying to look at the planet through a foggy window," said co-author and program PI, David Sing, a Bloomberg Distinguished Professor of Earth and Planetary Sciences at Johns Hopkins.
"Not only have we been able to clear the view, but we can finally pin down what the clouds are made out of and how they're condensing and evaporating as they move around the planet."
To study WASP-94A b, the team of researchers gathered data as the planet passed directly in front of its star. Using the high-powered, space-based JWST, the researchers were able to take separate measurements of WASP-94A b's leading edge as it started to cross in front of the star and the trailing edge as the planet completed its transit.
At the leading edge, the air flows from the night side of the planet to the day side, effectively making it the morning. Air flows from day to night at the trailing edge, making it the evening.
Observations revealed that mornings and evenings on WASP-94A b have extremely different weather patterns: mornings are riddled with clouds made of magnesium silicate, a common mineral found in rocks, while the evening has clear skies.
Researchers think one of two things could be happening. Powerful winds might lift clouds high into the sky on the cooler side of the planet and then plunge downward on the hotter dayside, dragging the clouds deep into the planet's interior and effectively burying them out of sight before sunset.
Alternatively, the phenomenon may be akin to morning fog burning off on Earth, but on an extreme scale. Clouds would form in the darkness of the planet's nightside. As they drift into the scorching heat of over 1,000 degrees on the day side, the chemicals that make up the clouds boil away, and the clouds simply vaporize.
Because the evenings are clear of clouds, the researchers could look to the trailing edge specifically to see what the atmosphere of the planet looked like-something the Hubble telescope could not provide.
Harry Baskett, from the University of Exeter and co-author of the research, said: "JWST provides us with exquisite observations of hot Jupiters and has recently been able to isolate the signatures of both morning and evening limbs on WASP-94Ab, information which is inherently 3D.
"For our group in Exeter, this is especially pertinent, as we use and develop a state-of-the-art 3D model, in partnership with our very own Met Office, to simulate the winds and all sort of physical and chemical processes driving the 3D structure of planetary atmospheres.
"It is really exciting to be able to combine observations and 3D simulations to distinguish weather patterns on exoplanets, infer the presence of clouds and constrain their formation mechanisms. Going forward, I hope that we can continue to combine observations and 3D simulations, to reveal more secrets about hot Jupiters."
When the researchers looked at the clear evening sky, they found that WASP-94A b was much more like Jupiter than they thought. Previously, when the clouds were averaged in, the data suggested the planet was made of hundreds of times more oxygen and carbon than Jupiter-a finding that baffled researchers given it couldn't be explained by planet formation theory. The new data, however, shows WASP-94A has only five times the amount of oxygen and carbon.
Hot Jupiter planets orbit much closer to their stars-closer even than Mercury to the sun-and therefore are much hotter and are exposed to more radiation. Because of their extreme environments, these planets also make good laboratories to study the chemistry and physics of cloud dynamics.
Using WASP-94 Ab as a benchmark, the team looked at eight other hot gas giants and discovered the same distinctive cloud cycle on two other worlds: WASP-39 b and WASP-17 b. Next, Sing and his team will be studying the cloud cycling across a wide variety of exoplanets using data from a new large JWST program, including an eccentric gas giant planet in the habitable zone.
Professor Nathan Mayne, also from Exeter's Department of Physics and Astronomy, added: "This exciting project shows the power of combining the exquisite observations from JWST with cutting-edge theoretical and numerical modelling of planetary atmospheres.
"We have been able to determine what the clouds are made of in the atmosphere of a planet 700 light years from Earth, which is crazy! This work also helps us to test, develop and improve our modelling approaches leading to improvements in Earth weather and climate prediction."
