While it is raining water on Earth, it is raining iron on KELT-20 b.

Marshall Johnson and I detected iron (i.e., Fe) in its emission form in 2023 as the planet is about to hide behind the star and as it reappears after the eclipse. The emission feature also suggests the existence of a stratosphere in the atmosphere of KELT-20 b. A stratosphere is a part of the atmosphere where the temperature increases with altitude, i.e., a thermal inversion.

In 2024, in a paper led by an OSU undergraduate student Sydney Petz, we thoroughly searched for all possible atomic and molecular species in the atmosphere. All elements with non-grey and non-blue colors could be detected if they exist, but only Fe and Ni were found.

In 2025, Sydney continued to investigate KELT-20 b along with other ultra-hot Jupiters and revealed a very compelling trend: all planets hotter than 2000 K exhibited thermal inversion AND Fe emission. These two phenomena were likely connected in that Fe is responsible for the thermal inversion in all ultra-hot Jupiters.

In 2025, we had another paper led by an OSU undergraduate student Calder Lenhart, who showed that Fe lines exhibited velocity change during the transit, beginning with redshift and ending with blueshift. This phenomenon, when combined with state-of-the-art general circulation models, will shed light on how atmospheric dynamics and magnetic fields affect 3D circulation on an exoplanet.