Astronomers can use ______ to learn about the composition of an exoplanet's atmosphere.

Astronomers can use ______ to learn about the composition of an exoplanet's atmosphere.

• A. Spectroscopy
• B. Photometry
• C. Astrometry
• D. Interferometry

Answer: (A)

Light carries the fingerprints of the atoms and molecules present, and spectroscopy is the way to read those fingerprints. By splitting light into a spectrum and looking for specific absorption or emission lines at characteristic wavelengths, we can identify which gases are in an exoplanet’s atmosphere. In practice, transmission spectroscopy is used when a planet passes in front of its star: some starlight filters through the planet’s atmosphere, and molecules absorb light at particular wavelengths, creating telltale dark features in the spectrum. Emission or reflection spectroscopy can also reveal these molecular signatures in the planet’s own emitted or reflected light. The presence and strength of these spectral features tell us which molecules exist and give clues about their abundances. Other methods measure different properties of the system. Photometry tracks how the total brightness changes, which helps determine size and orbital parameters but not chemical makeup. Astrometry monitors tiny shifts in the star’s position to infer mass and orbit, not composition. Interferometry improves angular resolution to image or resolve details, but it doesn’t directly reveal atmospheric chemistry.

Light carries the fingerprints of the atoms and molecules present, and spectroscopy is the way to read those fingerprints. By splitting light into a spectrum and looking for specific absorption or emission lines at characteristic wavelengths, we can identify which gases are in an exoplanet’s atmosphere. In practice, transmission spectroscopy is used when a planet passes in front of its star: some starlight filters through the planet’s atmosphere, and molecules absorb light at particular wavelengths, creating telltale dark features in the spectrum. Emission or reflection spectroscopy can also reveal these molecular signatures in the planet’s own emitted or reflected light. The presence and strength of these spectral features tell us which molecules exist and give clues about their abundances.

Other methods measure different properties of the system. Photometry tracks how the total brightness changes, which helps determine size and orbital parameters but not chemical makeup. Astrometry monitors tiny shifts in the star’s position to infer mass and orbit, not composition. Interferometry improves angular resolution to image or resolve details, but it doesn’t directly reveal atmospheric chemistry.