I was watching the video explaining how the planet K2-18b was showing strong evidence of life but I’m trying to understand how a telescope is able to grab the chemical composition of a planet so damn far? Does it act like a microscope from how strong it is?
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They wait for the planet to pass in front of its star and then they can see how the planet and its atmosphere interact with the star’s light.
Different elements absorb different wavelengths of light, so by analyzing which wavelengths get absorbed when the planet makes a transit, scientists can figure out what elements make up its atmosphere.
The different gasses will refract light through a Spectoscope in different patterns, and we can tell from these patterns what the composition of the atmosphere is.
Did you ever do the experiment in a science class where you shine a light through a prism and get a rainbow as the prism splits the light into all the different wavelengths?
Different gases absorb certain wavelengths of light, and they’re all unique like a fingerprint, so if we look at the light passing through a planet’s atmosphere and look at what’s missing from the spectrum when we split it, we can work out which chemicals the light has passed through.
The electrons around the nucleus of an atom are at particular energy levels. If an electron gets more energy, it can jump up to a higher energy level. To do this, it absorbs a photon, but it can only absorb a photon which has exactly the energy needed to jump from one energy level to another.
The exact spacings of energy levels depends on the element. The wavelength of a photon depends on the energy of that photon. So, each element absorbs only the wavelengths which correspond to the gaps between energy levels for that element. These are called ‘absorption lines’ because if you use a prism to split light into a spectrum, they show up as dark lines in the spectrum.
This means you can tell what elements are present in something that light has passed through by looking at the pattern of dark lines in the spectrum. This is called “spectroscopy”.