What technique did Hubble use to analyze the chemical signatures in exoplanet atmospheres?

Analyzing starlight filtering through the atmosphere during a transit

While ground-based instruments often excel at discovering exoplanets through transit photometry (detecting dips in starlight) or radial velocity methods, Hubble played a crucial role in the characterization phase. Specifically, when an exoplanet passed directly in front of its host star—an event known as a transit—Hubble was positioned to capture the starlight that passed through the thin ring of the planet's atmosphere. This process, spectral analysis, allowed astronomers to identify the chemical fingerprints of various elements and molecules, such as water vapor, methane, and carbon dioxide, based on the specific wavelengths of light absorbed by those atmospheric components.