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)
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Astronomer here.
It **has not definitively detected this gas, dimethyl sulfide.** The scientific paper makes no claim that it has been detected, and neither does the official press release. The data *might* hint at it. Or it could be a fluke. It’s at the level of the noise. They need more data to be able to tell. It could **very easily** turn out to be nothing.
There are also lots of reasons to think there is no life on this planet. The possible liquid ocean is under a thick atmosphere, which means it’s much hotter and at higher pressure than oceans on Earth. This is a problem for any life we understand, because proteins like DNA and RNA denature at these temperatures. So it’s waaaaaaaaayyyy too early to go around saying life has been found.
Reading the paper, it looks to me like the scientists are laying the groundwork for asking for more telescope time with a different instrument setup to look for this molecule specifically. Good luck to them.
Anyway… all molecules interact with different wavelengths/colors of light in different ways. They leave “fingerprints” on the light where they have absorbed certain colors. The scientists who studied K2-18b think there could be hints of the fingerprints of a molecule called dimethyl sulfide, which on Earth is made by life. If it turns out that it is on K2-18b after all, that would be exciting because we don’t know a good way to make lots of that molecule with other processes besides life. Which doesn’t necessarily mean there’s no other way to make it!
What gas did they detect, and is it impossible for it to be made in the absence of life?
I wonder how many of these nasal announcements are just plain false.
Whose going to prove them wrong?
This is my favourite part of astrophysics. Google “Fraunhofer lines”.
Emitted light, when we look at its wavelength spectrum, will contain missing “lines”, like a barcode.
The missing bits let us determine the elements that source of light has interacted with. This is how we know the makeup of Neptune’s atmosphere, for example.
When a planet passes in front of a star, even if the planet is absolutely tiny compared to the star, the overall brightness we see from the star drops a teeny tiny bit. In most cases, this isn’t even detectable on non-specialized equipment. Our telescopes looking for exoplanets are specifically designed to be sensitive enough to detect these dips in brightness.
Then, certain gasses absorb certain wavelengths of light. When white light (presence of all wavelengths) passes through a gas, some of the light doesn’t come out, but only certain wavelengths. When looking at the brightness of individual wavelengths, there will be seemingly random valleys compared to the rest of the light curve. We call this an absorbtion spectrum, and it can act as a kind of fingerprint for gasses (in this case. This phenomenon isn’t exclusive to gasses).
So not only is the body of the planet lowering the brightness across the spectrum, but the atmosphere will cause certain wavelengths to drop even more. We can see where these valleys of brightness are and match them to known absorbtion spectrums and get the atmospheric composition.
An actual ELI5 answer:
Remember the pretty colors a prism makes? Like a rainbow? If you hold a magnifying glass up to the rainbow you will see dark lines, like a barcode! When light passed through these gasses, like Oxygen, dark lines form in the rainbow. Different gasses have different barcodes! We can read these barcodes to tell what types of gasses are on other planets!
Our telescope can see distant light, put it through a prism and then read the barcode to tell what gasses that light passed through!
Obviously much more complicated than that but you’re 5 years old..now go outside and find some frogs or something.
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