Are there Spectral Features in the MIRI/LRS Transmission Spectrum of K2-18b?

Abstract

Determining the composition of an exoplanet atmosphere relies on the presence of detectable spectral features. The strongest spectral features, including DMS, look approximately Gaussian. Here, I perform a suite of Gaussian feature analyses to find any statistically significant spectral features in the recently published MIRI/LRS spectrum of K2-18b (N. Madhusudhan et al. 2025). In N. Madhusudhan et al. 2025, they claim a 3.4-$\sigma$ detection of spectral features compared to a flat line. In 5 out of 6 tests, I find the data preferred a flat line over a Gaussian model, with a $\chi^{2}_{\nu}$ of 1.06. When centering the Gaussian where the absorptions for DMS and DMDS peak, I find ln(B) = 1.21 in favour of the Gaussian model, with a $\chi^{2}_{\nu}$ of 0.99. With only $\sim$2-$\sigma$ in favour of Gaussian features, I conclude no strong statistical evidence for spectral features.