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 simplest way to explain it is they break down the light that is passing through the atmosphere of the planet. Different gases have different effects on how light passes through them. With the right equipment, and most importantly knowledge, they can identify a lot of what an atmosphere is made of from amazing distances.
Because the sky is blue (on Earth).
Transparent materials, like air and water, aren’t perfect; they absorb and/or bend different wavelengths of light by different amounts. So if we can detect light that’s gone through the atmosphere of an exoplanet, we can compare that to light from the planets star to see how it’s been changed. If it bends/absorbs light in specific ways, we can tell that a specific gas is present.
Think of a [neon sign like this.](https://www.pinterest.com/pin/633600241313896739/) How do they make the different colors?
What’s happening is one of the most approachable parts of a vastly complicated branch of physics called “Quantum Mechanics”. In a very ELI5 explanation – when you give something energy, it glows. Usually things don’t glow so that human eyes can see them, like I’m not glowing at the moment, am I? But wait! There are “infrared goggles” you can wear when I am glowing So every glows if it has energy, including the gases in a planet’s atmosphere.
Back to the neon signs – the elements in the gas and the molecules they form, *glow different colors*. Neon signs glow reddish, argon glows blue/green, etc. Even when we can’t see the colors with our eyes, we can detect them with special cameras.
So that’s what’s happening here, a telescope took a picture of a planet, they matched the colors of the gases to known colors of gases like picking out paint samples at Home Depot. BOOM! We know what gases are in the atmosphere!
Certain gases, like Methane break down pretty quickly in the atmosphere, so without a steady supply there would be very little left. On Earth we have tons and tons of grass eating animals that fart out vast quantities of methane and any alien would be able to instantly know there was life on Earth be seeing the cow-farts.
In a similar we scientists are looking at the planet in your source and seeing other ‘proof of life’ chemicals. Again, not conclusive, but really interesting and promising.
When atoms or molecules emit or absorb energy, this energy comes from/goes into vibrations that they perform. A given atom or molecule has a series of very specific frequencies corresponding to different kinds of vibrations (e.g. in a water molecule, you can get a vibration in which the molecule bends, one in which it stretches, etc.). It will be especially good at emitting/absorbing radiation at those specific frequencies (this is similar to how bridges have resonant frequencies at which they are very good at absorbing energy from external vibrations).
So when light from a star passes through a planet’s atmosphere, some frequencies get absorbed much more than others. By splitting the light coming from a planet into different frequencies with a spectrometer, and comparing the results with what you see in a lab when you pass light through a known sample of gas, you can tell which atoms and molecules are there. However, there are two complications:
* the light coming from a distant object will be red-/blueshifted by the Doppler effect, so the frequencies will not be exactly the same as you see in the lab, but will all be shifted by the same amount
* the light that has passed through the planet’s atmosphere will be swamped by the light coming directly from the star (which has its own pattern of absorption from the gas in the outer layers of the star) – there are some different ways of dealing with this. One thing you can do is compare how the absorption spectrum changes over time as the planet passes in front of the star. It’s also possible to use coronagraphy to block out some of the light from the star, which simply involves placing a carefully positioned object in front of the telescope.
It amazes me all of the science that had to happen, building on each other findings, over decades …. to get to a point where we can tell what gasses are on a distant plant by how the light passes through them. So cool and really not appreciated (I think)
I recommend watching Niel de Grasse Tysons, Cosmos – a spacetime odyssey to fully grasp how mind blowing this is. Episode 5 “Hiding in the light”.
[this video](https://youtu.be/gVZwdYZqCUI?si=67fe_IaIBULGsoBn) has some more specifics as to how we know what materials distant celestial bodies are made from and how that is synonymous with the light we can see coming from distant planets.
Each element eats up a certain colour in the rainbow. So we can look at the light coming in from a planets atmosphere, divide the light up into a rainbow using something like a prism, and check which colours are missing. We use that like a chemistry map to tell us which elements the planet is made out of.
Every chemical absorbs/emits a unique set of colours of light.
That orange colour you often see in older streetlights? That’s specific to the metal sodium. Only sodium produces that exact orange colour.
Spectrographs are machines that measure the different colours of light that hit them in very fine detail.
A good spectrograph can easily tell apart two colours of light that differ only very slightly, this makes them really good at identifying specific chemicals by the colours of light they absorb.
So we attach a spectrograph to a big telescope. Now we can see all the different colours of light it detects in very fine detail.
We point the telescope at a star with a ‘transiting’ exoplanet, which means the exoplanet briefly passes right in front of the star during its orbit, as seen by our telescope on Earth.
This means for a brief period of time, there is a huge amount of light from the host star shining through the exoplanet’s atmosphere.
Some specific colours of this light will get absorbed by the various chemicals in the planet’s atmosphere, and we will see the effects of this absorption when we look at the data from the spectrograph.
Now we can compare the various absorbed colours to huge databases of known chemical absorption spectra, to identify which chemicals are in the planet’s atmosphere.
In this specific instance, scientists *THINK* they have detected a chemical that is only produced on Earth by living creatures.
That’s not to say the chemical can’t be made naturally on any planet, it probably can somewhere, just not on Earth as far as we know.
This detection is sufficiently weak that there’s a reasonable chance it’s due to random noise instead of a real detection.
Stand by the side of a lightly traveled road and close your eyes.
Listen to the sounds of cars passing you by.
There’s so much information in what you hear. You can tell which direction the cars are moving, how fast. You might be able to hear what kind of engine it has.
Light has information too. Vast amounts of information.
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