Nightside clouds reveal new insights on giant exoplanet Wasp-43b

Nightside clouds reveal new insights on giant exoplanet Wasp-43b
by Sophie Jenkins
London, UK (SPX) May 01, 2024

Researchers from NYU Abu Dhabi's Center for Astrophysics and Space Science, including Research Scientist Jasmina Blecic and Associate Professor Ian Dobbs-Dixon, have revealed significant findings from their study of WASP-43b using NASA's James Webb Space Telescope. Published in Nature Astronomy, their research highlights the first observation of dense, dust-like clouds on the nightside of this Jupiter-sized exoplanet and notes an intriguing absence of methane.

Utilizing the Mid-Infrared Instrument (MIRI) on Webb, the team analyzed the full orbital phase curve of the planet, focusing on temperature fluctuations and chemical compositions across its atmosphere. Despite the constant shadow over its nightside, WASP-43b maintains a high temperature around 600C, indicating robust heat redistribution driven by intense winds, which are significantly stronger than those on Earth.

"We observed this planet while it orbits around its star using an infrared spectrometer, so that we could study the light emerging from the different regions of its atmosphere," explained Blecic.

"This allowed us to distinguish between the day and nightside temperatures, and identify the presence of clouds and various molecules. Different chemical species absorb light at different wavelengths in infrared. Combining this fact with observations of the entire orbit, we were able to constrain the chemical composition, cloud coverage and heat redistribution across the whole atmosphere and draw conclusions about the planet's climate."

The research challenges earlier models by showing a thicker cloud layer on the nightside than previously expected, effectively blocking significant amounts of infrared radiation. Additionally, the presence of water was detected, further illustrating the clouds' unusual height and density. The study also underscores rapid chemical mixing in the atmosphere due to the planet's severe temperature contrasts, driven by its close orbit to its star, which completes in only 19.5 hours.

"The absence of direct sunlight on the planet's nightside causes significant temperature differences between the day and night sides, which prompts the formation of exceptionally strong winds," noted Dobbs-Dixon, an expert on three-dimensional atmospheric models and heat redistribution in exoplanetary atmospheres.

"While winds on Earth form in a similar manner due to variations in temperature, the close proximity of WASP-43b to its host star results in much more extreme temperature differences. This produced winds of thousands of kilometers per hour, far surpassing those on Earth, crucial for the distribution of heat and shaping the overall planetary climate."

Caption 1. top image
This set of maps shows the temperature of the visible side of the hot gas-giant exoplanet WASP-43 b, as the planet orbits its star. The temperatures were calculated based on more than 8,000 brightness measurements of 5- to 12-micron mid-infrared light detected from the star-planet system by MIRI on NASA's James Webb Space Telescope. The planet's proximity to its star results in a tidal lock, with one side continuously facing the star and the other in darkness, creating stark temperature differences. Temperature maps indicate an average temperature of 1,250C on the dayside and 600C on the nightside, with strong equatorial winds influencing the hottest points of the planet.

Caption 2. lower image
This light curve represents the change in brightness of the WASP-43 system over time as the planet orbits the star. The brightness peaks when the hot dayside faces the telescope and dims as the nightside rotates into view. Over a 24-hour observation period, Webb's MIRI captured more than 8,000 measurements in low-resolution spectroscopy mode, enabling precise calculations of temperature variations on the planet.

Research Report:Nightside clouds and disequilibrium chemistry on the hot Jupiter WASP-43b