russ_watters said:
I don't think I'm going to find that sort of discovery compelling.
Yeah. There have been several of these this might indicate life discoveries in thee last few years. To some degree they all seem equivocal. Possible non-biological ways to make particular chemicals are difficult to eliminate.
russ_watters said:
I had been thinking there might be unequivocal chemical signatures we could detect with telescopes from light years away.
There is a different potentially useful approach however. It is called
assembly theory and is based being able to identify products of life spectroscopically which can be (in theory) done with telescopes (if enough of the molecules are present). The main argument is that non-biological reactions may produce a bunch of chemicals but they will be not of a single type of chemical, but a very complex mix of chemicals, unlike the select set of chemicals found in living things. An often cited example is what was found in the
Murchison meteorite which has a lot of organic compounds. Although there are many kinds of chemicals found in biology (on earth), there are also a lot of others. This has been compared to tar (as opposed to life).
Biological processes on the other hand will make lots of chemicals on a much more limited range of types. These higher concentrations of fewer types on chemicals might be detectable. They think of this as the copy number of a chemical species. This indicates how focused production is on the particular kind of chemical. The higher copy number, the more the chemical is being produced rather than other chemicals.
Those that like these ideas think that only life could get through the may steps (15 or more) required to assemble the chemicals from more primordial chemicals (thus the name assembly theory). They figure that chemicals requiring 15 or more assembly steps (steps of chemical synthesis) would be clearly due to life processes and not abiotic in origin. Thus making it a good biomarker at distance. They have been doing experiments in labs on this process of chemical exploration of chemical structure space.
I am pretty sure that this is a NASA funded approach, but I don't think it is actually being used to search space for like at this time.
What I described above in post #2 of this thread is basically the wet rock planet approach. Where water and basaltic type rock come together
serpentization reactions can produce simple organic compounds. This is a NASA favorite and is considered a likely basis for life arising on Earth and the basis of looking for (Earth-like) life on many planets, such as Mars (formerly wet, possibly still so on the inside) and Enceladus (thought by some to have a solid center, surrounded by an ocean under a layer of ice). These kind of reactions have been seem on Earth and in labs. In addition, greigite (which can act as a catalyst for some of these reactions) is a naturally occurring mineral. Simple organic chemicals can be produced in this manner, but not a living process.
There may be other ways to made the chemicals needed for Earth-like life. There may also be other kinds of life chemically distinct. No one knows and our negatives are neither informative nor convincing (to me anyway). Assembly theory can (in theory) get around this problem.
On the other hand assembly theory is not a theory about how life works and the steps it went through during its emergence. So it says nothing about these mechanisms and is only concerned what is statistically unlikely enough (for non-living processes to make) to have to have been made by life.
What would be more convincing and fulfilling (to me) would be:
- bring back materials so they could be studied in labs on Earth, or
- take people to Mars and do lab stuff there, or
- make much more sophisticated robots and Martian labs to study things on Mars without people there.
What was found on Mars is basically a fossil of which only the chemistry and some not too detailed structure could be studied. Sectioning rocks and looking at them under a nice microscope would be more informative.
Even then there is the issue of clearly identifying life if you were to find it. Near the border between living and non-living this can be difficult.
If I were deciding what to do, I would get people (or highly capable robots) on Mars with a drilling rig an start sampling subsurface areas where liquid water might exist. (Earthly life has no problem living far under ground.) Being subsurface would. protect the life forms from the bad space stuff (UV etc.) and there would be chemicals there they could eat. That's where I would thing life would be on Mars if its there. The samples could be then analyzed in Martian labs by the robots or people.
There are also planetary protection procedures to follow to avoid contaminating Mars with Earth life. These make everything more difficult (like collecting samples) and could be interpreted as ruling out putting people on Mars at all (due to contamination hazards).
