ASK Space
EXOPLANETS
How do scientists study the atmospheres of exoplanets?
Most exoplanets are too dim to detect directly, so scientists study their atmospheres indirectly by observing the effect the planetary atmosphere has on starlight. Transiting planets are the best for atmospheric studies. These are planets with orbits aligned so that the planet passes exactly between us and the planet’s host star. While we can’t actually see the planet, we know it exists because it blocks a fraction of the starlight: this dip in brightness is called a transit.
The planet’s atmosphere appears as a translucent ring hugging the opaque disc of the planet. It acts as a filter: the chemicals present in the atmosphere absorb certain distinct, precisely defined colours of light. Quantum mechanics causes each chemical to create a characteristic absorption pattern of colours, which acts like a chemical fingerprint. This allows astronomers to measure chemical compositions by spreading light out
