The team even managed to calculate how the atmosphere keeps the clouds aloft. The equatorial wind is apparently strong enough to push the heavy mineral droplets through the night side faster than gravity can pull them down.
Finally, the researchers ran an experiment where they took their precise JWST data and reanalyzed it without splitting it into two to resolve the limbs. “This had a huge effect on our understanding of the composition of this planet,” Mukherjee says. The results the researchers got when they averaged the atmosphere in a traditional model turned out a bit alarming for exoplanet science in general.
Biased composition
Because the thick morning clouds diluted the clear water vapor signals from the evening, the single-sphere model concluded that the planet’s metallicity—the abundance of elements heavier than hydrogen and helium—was suspiciously high. “With the limbs resolved, we’ve got an oxygen enrichment of this planet that was three to five times higher than our Sun,” Mukherjee explains. When the team averaged the spectrum, the oxygen enrichment came out about 100 times higher.
This bias in the composition estimates, he argues, probably affects other tidally locked exoplanets, including sub-Neptunes and super-Earths that are smaller than WASP-94A b. For now, though, we have not been able to resolve the morning and evening asymmetries in these smaller planets, even using the JWST. But the team thinks there is still a lot we can do before concluding we need an even bigger telescope.
“We need to think harder about how to mitigate this bias,” Mukherjee says. The answer, he suggests, might be figuring out how to disentangle morning and evening limbs in smaller planets based on the data we get from the instruments we have. “And even if we don’t have this kind of measurements, we can think about how to develop our theoretical models to mitigate this even if we have an averaged spectrum of the planet,” Mukherjee claims.
Science, 2026. DOI: 10.1126/science.adx5903
