Transmission spectroscopy

Spectroscopy is the technique of splitting received starlight into its different colours using a prism. Exoplanets orbit their stars, when they transit – pass by from our point of view – some of the starlight passes through the planet’s atmosphere. Particles in the atmosphere like water vapour, carbon dioxide, methane and others absorb some of that light. This absorption happens at specific wavelengths of light. By studying at which wavelengths the starlight is absorbed, we can determine what kind of particles are present in the atmosphere. The NASA/ESA/CSA James Webb Space Telescope uses this technique to characterise exoplanets and ESA’s Ariel mission will study the atmospheres of as many as 1000 exoplanets this way. Both missions focus on infrared light because the signatures of molecules are very prominent in those colours.

Acknowledgement: Work performed by ATG under contract for ESA