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
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.
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