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 dimethyl sulphide (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. In N. Madhusudhan et al., they claim a 3.4 σ 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 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mi>χ</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>ν</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>2</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> 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 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mi>χ</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>ν</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>2</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> of 0.99. With only ∼2 σ in favour of Gaussian features, I conclude no strong statistical evidence for spectral features.