The Futility of Exoplanet Biosignatures

[Genady]

I've just stumbled upon this new paper draft, [2205.07921] The Futility of Exoplanet Biosignatures (arxiv.org) and immediately thought of @beecee because of this statement in the abstract:

Technical constraints and our limited access to other worlds suggest we are more likely to detect an out-of-equilibrium suite of gasses than a writhing octopus. Yet, anything short of a writhing octopus will raise skepticism among astrobiologists about what has been detected.

[joigus]

So we need a theory of life, or a definition at least.

In the absence of that, what chemical would our distinguished members consider to be a dead giveaway? --Puns aside.

[beecee]

10 hours ago, Genady said:

Yet, anything short of a writhing octopus will raise skepticism among astrobiologists about what has been detected.

6 hours ago, joigus said:

In the absence of that, what chemical would our distinguished members consider to be a dead giveaway? --Puns aside.

The best we can do is say that conditions exist or once did exist, to support the existence and evolution of life, as we know it. Not until we discover an undeniable Alien relic or fossil, ascertain undeniable constructions such as cities, bridges, or vehicles, or of course actual physical contact, can we be really certain.

Extraordinary claims, require extraordinary evidence.

Edited May 18, 2022 by beecee

[joigus]

You set your standards very high, @beecee. Finding a fossil is hard enough on Earth!

Just a molecule that couldn't conceivably have been produced by geology wouldn't be enough?

[beecee]

18 minutes ago, joigus said:

Just a molecule that couldn't conceivably have been produced by geology wouldn't be enough?

Yes, you can add that to the list also. 

19 minutes ago, joigus said:

You set your standards very high, @beecee. Finding a fossil is hard enough on Earth!

My number one wish before I kick the bucket, is that the extraordinary confirmation of ETL is found and validated as such. Why shouldn't the standards be very high, considering it would be answering mankind's greatest question?

6 hours ago, joigus said:

So we need a theory of life, or a definition at least.

Oparin - Haldane theory' Abiogenisis.

[Genady]

I think, if we could detect something like DNA or a ribosome, that would be sufficient.

[Ken Fabian]

We will get samples from within the solar system but it looks unlikely in the extreme that we will ever get to examine samples from exoplanets, ever - so we will have to make do with what astronomy can detect. If we want evidence of ETL within our lifetimes it has be either artificial emissions - intentional and unintentional - or biosignatures, not samples.

I am not sure what is meant by "theory of life" - observed and hypothetical biological chemistries? I suspect there will be limited chemical pathways for abiogenesis to make life and that determining what those are (and how limited) will be primarily a matter of modeling. Of course we will need to know what signatures abiotic processes can produce, to reduce the possibility of misreading signatures that are ambiguous.

[Genady]

The authors compare "theory of life" to theory of gravity; a theory that would allow to make predictions and to direct research regarding life in general, unlike biology which is a "theory of life on Earth." They mention a path to develop such theory by creating forms of life in a lab.
I think it is possible to get samples from exoplanets via interstellar asteroids. Not within our lifetime, though.

 

[Prometheus]

Assembly theory posits that complex molecules found in large abundance are (almost surely) universal biosignatures. 

From their publication: https://www.nature.com/articles/s41467-021-23258-x

 

At the moment it only has proof of concept with mass spectrometry, but it's a general theory of complexity so could work with other forms of spectroscopy. Interesting direction anyway.

[Moontanman]

Any bio markers seen by telescope would have some doubt attached to them. Right now there is a biosignature on Titan and a pretty good idea of how life could be possible in liquid methane/ethane. We will have to visit Titan either by robot or in person to be sure.  

[swansont]

On 5/24/2022 at 5:54 AM, Prometheus said:

Assembly theory posits that complex molecules found in large abundance are (almost surely) universal biosignatures. 

How does assembly theory deal with/explain the Miller-Urey experiment?

[Prometheus]

6 hours ago, swansont said:

How does assembly theory deal with/explain the Miller-Urey experiment?

Dunno, but the PI of that nature paper is very active on twitter: he came up with the idea and would probably answer your question.