I just can’t compute how this is possible. How can a telescope detect a gas, which isn’t even visible to the naked eye, on a planet that is an incomprehensible distance away.
[Source](https://www.bbc.co.uk/news/science-environment-66786611)
In: 143
The telescopes don’t see the gas any more than your eyes see our own atmosphere, but that doesn’t mean things are unknowable. We see trees and flags wave in the wind, and clouds form and move, we have rainbows and light pollution, stars twinkle — all consequences of gasses we can’t see (but we do see the results). The question of understanding distant planets works in the same way, we can understand the gasses and atmosphere even without seeing them directly IF we can get an idea of what the gasses are doing via other methods.
In the instance of this telescope & planet, the telescopes take a picture of the star and then another and another (and so on) looking for little eclipses from when the planet crosses in front of the star from our point of view.
And when THAT happens we can get a picture that includes the planet. And if we’re lucky, we can catch a hint of the rainbow created by the planet’s atmosphere (if it has an atmosphere). This works much the same way as a rainbow here on Earth.
And if we have a rainbow (a spectrum) THAT can be analyzed to see what is causing it, as not all rainbows are created equal. On their face, all rainbows look similar, but that is partly because the light rays are going every which way. If you have a polarizer (like polarized sunglasses) you can filter out the “every which way” effect and you get a rainbow with a long series of dark & bright spots, I’ve linked the periodic table of elements so you can see what each different element’s ‘fingerprint’ looks like in this situation; and of course each molecule has a different fingerprint as well.
[Periodic Table of Elements](http://2.bp.blogspot.com/-rh08lgewe08/UdpI0-NbEAI/AAAAAAAAAFI/2_SRy2xEEZA/s400/spctelem.png)
[What our sun looks like](https://image.slidesharecdn.com/spectroscopy-090508075019-phpapp01/75/spectroscopy-12-2048.jpg?cb=1669870731) (other stars, and planets) will have their own unique combinations.
By examining the fingerprints in the “rainbow” scientists can determine what gasses are causing that particular appearance even without seeing the gasses directly.
If you want to know how each element results in a different fingerprint, that’s a little more involved, but a simple (and very incorrect) analogy is to imagine that each set of electrons creates a kind of “shadow” that affects a very narrow slice of the spectrum, and because each element and each molecule have a unique combination of electron configurations…you can get a unique “shadow” pattern in the rainbow. They are *not* shadows, but explaining the physics behind is more high school science than ELI5 and should be its own question.
Every single element has a spectra of light that is unique to that element. Think of this like a visual “fingerprint” for elements. Scientists have conducted experiments on all of the planetary elements and empirically figured out the different emission spectra for each element.
These emission spectra https://en.m.wikipedia.org/wiki/Hydrogen_spectral_series are what scientists are measuring when trying to determine the composition of a distant planetary body. The telescope revives the light from the object by observing it, and then the scientists can break down that information to figure out what the object is made of.
In the spirit of ELI5, here’s a relatively simple explanation:
Scientists on Earth have tested what happens to light when it passes through gases. We know that when a beam of white light passes through a gas, the beam coming out of the other end will be missing some of its colors.
Each unique gas will remove a unique set of colors in the exact same way every time, so you can think of these missing colors as the gas’s “signature”.
We’ve done this for pretty much all gases, so we know what each gas’s signature looks like.
Now, when observe the light from a distant planet, the light we observe will also be missing some colors. If you look at the missing colors, you can find out what gases the light passed through using the gas signatures we already know.
It doesn’t matter how far away the planet is, all we need is a single beam of light to be able to analyze the missing colors and find the gas signatures.
With this method we can then conclude what gases are present in a planet’s atmosphere.
The most simplistic way I can put it is light gets absorbed by particles as it passes through. Each element absorbs a different wavelength of light. All we have to do is look at the light coming off the planet and see which wavelengths are missing. This tells us the light passed through that gas, thus telling us what gases are on/around that planet.
Is it in Alpha Centauri?
Light from a broad spectrum source produces a full rainbow spectrum, but as this light passes through any gas, that gas absorbs certain frequencies of light, resulting in slight dark patches on the spectrum. See this video explanation:
# VT.Physics | [Emission and Absorption Line Spectra – A Level Physics](https://www.youtube.com/watch?v=jsNkcCyrxvU)
For example, when people say that CO2 is a greenhouse gas, and that it traps heat, what this means is that infrared light on the light spectrum gets absorbed by CO2, and gets re-radiated. So heat from the earth, after it has been warmed by the sun, which would normally be re-radiated into outer space as infrared, gets absorbed by the CO2 in our atmosphere, and gets re-radiated in all directions as a sort of infrared glow in the sky, kinda like how our sky is blue, where a mix of light, primarily blue light, gets absorbed and re-radiated in all directions by our atmosphere.
This is how we can optically assess the composition of our atmosphere. Every type of gas has its own fingerprint of a line spectrum.
This is possibly a dumb question: If the planets we observe are theoretically in the past, does that mean the elements we observe on the planet are also in the past?
Oooh I just watched a video on this topic recently!
Depending on the gasses on that planet, they will absorb different wavelengths of light. This means that we can split the light and look for missing colours in the resulting rainbow. And compare to know gasses on earth that leave the same signature pattern.
[Be Smart – Why some of the rainbow is missing](https://youtu.be/gVZwdYZqCUI?si=QClHpArJ3abiGoRS)
They’ve also been doing a scientific UAP study and are supposed to be making an announcement on Thursday.
”I’m optimistic that we will one day find signs of life.
“Signs of life as we know it”. So many articles leave this part of the sentence out.
Space is a big place. There may very well be different kinds of “Life”.
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