Scrutable

discovolante wrote: Sun Apr 20, 2025 11:05 am

dyqik wrote: Fri Apr 18, 2025 12:44 am

jimbob wrote: Thu Apr 17, 2025 8:07 pm
I can think of several ways that could be, but in what ways is it weak?

At the most fundamental level, it's a 3 sigma detection of DMS, when 5 sigma is the default for claiming a real detection.

Claiming that DMS must be a signature of life is very wrong. DMS has been detected in comets and the interstellar medium, and it definitely didn't come from life there.

Where does DMS in the interstellar medium and comets come from?

I think it's more that DMS would normally break down in planetary atmospheres, so its continuing presence is indicative of life processes. Similar to finding free molecular oxygen in an atmosphere, I guess.

quoted rather than edited, so deleted

The idea we could deduce the existence of life because we detected some fairly simple organic chemical on an extrasolar planet strikes me as lacking any basic kind of scientific scepticism. You see these kinds of claims fairly regularly, and I had my usual reaction to it.

To take an example of what kind of really complex stuff can exist, and persist deep in a planetary crust to leak out much, much later, I think it has been satisfactorily demonstrated that oil can occur abiotically on earth. I think it is reasonably clear that most, probably all, of the oil on earth is biotic. Nevertheless, we thus learn some really rather complex, and life-imitating, chemicals can occur abiotically. Indeed, the first chemicals that life was put together from must, by definition, have been abiotic. Some very life-like stuff can be abiotic.

Every time we sent a probe to another body in this solar system, we were astonished with what we found. Extrasolar planets have ranges of conditions well outside our experience from what we have seen in this solar system. Some stuff that would astonish us probably goes on there, perhaps including some surprising chemistry.

Remember the nonsense about phosphine on Venus? https://en.wikipedia.org/wiki/Life_on_Venus#Phosphine

Gfamily wrote: Sun Apr 20, 2025 11:30 am

discovolante wrote: Sun Apr 20, 2025 11:05 am

dyqik wrote: Fri Apr 18, 2025 12:44 am

At the most fundamental level, it's a 3 sigma detection of DMS, when 5 sigma is the default for claiming a real detection.

Claiming that DMS must be a signature of life is very wrong. DMS has been detected in comets and the interstellar medium, and it definitely didn't come from life there.

Where does DMS in the interstellar medium and comets come from?

I think it's more that DMS would normally break down in planetary atmospheres, so its continuing presence is indicative of life processes. Similar to finding free molecular oxygen in an atmosphere, I guess.

We find atomic oxygen in the earth's upper atmosphere, due to UV dissociation, and auroral activity. The red aurora are atomic oxygen recombination lines.

https://www.nps.gov/articles/-articles-aps-v8-i1-c9.htm

Lots of weird chemistry happens in the upper atmosphere of earth, in the interstellar medium and in molecular clouds in star forming regions, due to the low pressures and UV photon bath.

Interesting, thank you.

Question arising from that, and apologies that this isn’t really astronomy and space, but do we only have an ozone layer because of the amount of molecular oxygen in the atmosphere? Would ozone form in a CO2 rich atmosphere?