How are we able to determine the composition of our orbiting planets?
Asked by: J.J. Yrue


Essentially we look at the light being reflected from the planet. This is called spectroscopy and it involves looking at the wavelengths of all the photons that are coming from the planet. Each element emits light at a characteristic wavelength that can be determined in a lab here on earth. so we just match up the wavelengths of incoming light with the wavelengths we know, and then determine the composition of the planet, and its relative quantity of each element.
Answered by: Mike Perkins, Physics/Astronomy Major, Penn State

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