My gf and I are just confused cos the best two telescopes out there are hubble and JWST, right? And they’re great at what they do respectively, but how the hell do we know that a planet millions of light years away has an atmosphere made up of x.
Was prompted because of an article which said “It may have detected a molecule called dimethyl sulphide (DMS). On Earth, at least, this is only produced by life. “ like how tf can we detect a MOLECULE that is so far away.
My guess is colours but no clue.
In: 29
Your guess is right. When you shine a light through a gas, the gas will absorb certain wavelengths of light. This is called the gas’s absorption spectrum. If we look at a planet while it is passing in front of its star, the light from the star will shine through the atmosphere and travel to our telescope, and we will see all the frequencies of light *except* for the ones that the planet’s atmosphere absorbs. We can then match that spectrum to all of the gases we have tested on Earth, and find the one that lines up.
You’re right, it’s colors.
But probably not in the way you’re thinking.
The planet orbits a star and that star has a specific spectrum of light.
When the planet orbits near (or if you’re lucky, transits) the parent star you can get a measurement of the star’s light that has passed through or bounced off the planet’s atmosphere.
This gives you the same spectrum as the parent star but with a few very specific wavelengths (colors) missing – wavelengths that correspond to the light absorbed by the molecules in the atmosphere.
If the wavelengths that dimethyl sulfide absorbs are present in the starlight but missing from the planet, you can conclude that the molecule was present in the atmosphere and absorbed it.
>My guess is colours but no clue.
Pretty much.
Different molecules interact with light differently, absorbing or emitting light at different frequencies (colours) dependent on the properties of the molecule. We call these the spectral absorption/emission lines.
The hydrogen atom is a good example:
https://en.wikipedia.org/wiki/Hydrogen_spectral_series
Telescopes like the JWST have what’s called a spectrometer, which “splits” the light into its constituent frequencies so that you can then compare the relative intensity of each frequency. Doing this reveals spectral lines, which can then be matched to molecules that we have studied in labs.
Basically, you’re right: we look at the spectrum of light from the source, and we can make good guesses about what gases compose its atmosphere.
Gases absorb and emit certain frequencies of light more than others. It’s how we figured out what’s in the atmospheres of stars: gases that are energetic enough emit light, and cool enough absorb light, in ways that create bright or dark bands in the normal spectrum.
Atoms have different masses and charges depending upon what element they are.
This leads to light getting absorbed or emitted by different kinds of elements differently, and essentially acts like [fingerprints of light](https://en.wikipedia.org/wiki/Spectral_line#Spectral_lines_of_chemical_elements).
The way that molecules hold multiple atoms together also causes light to be absorbed or emitted by different kinds of molecules in different ways. So that acts like yet another kind of light-based fingerprint.
When a planet passes between its sun and us, some of the light passes through the atmosphere on its way to us. By looking at how the light changed we can start to deduce the chemical composition of the atmosphere
What you have to understand about those telescopes is that they’re not looking in the visible light spectrum. When you get into multispectral or hyperspectral imagine you’re taking multiple measurements for each pixel in hundreds of different wavelengths to measure things like composition. That’s what JWST is doing. It’s not looking out and taking really great photos. It’s taking hundreds of measurements in each pixel that are then calculated against known values for certain compounds.
The Teaching company has a good series on this topic on Audible. I think it’s titled exoplanets.
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