With SOSS mode, the NIRISS instrument will be able to study the atmospheres of exoplanets as they pass in front of their star using a technique called transit spectroscopy. The spectrum observed by NIRISS will act like an alien barcode, indicating the presence of certain atoms and molecules. The above illustration shows how absorption features due to sodium (Na) and potassium (K) can be seen in the visible light spectrum; Webb’s infrared light observations will be sensitive to other features such as water vapor, carbon dioxide, and methane. (Credit: European Southern Observatory)