Did you read the URL I provided? Those are Levin’s arguments, not mine.

Yes, I read it; I was referring to when you argued for radio-labeling carbon in search for redox reactions, more specifically photosynthesis, just as Levin does.

What has taken NASA so long to resume the search for life on Mars?

I’m not an expert here, but it seems to me there was a long hiatus in exploring Mars for political reasons. I assume most would blame the negative results from the expensive Viking landers, which we know now was due to the overoptimistic design of the experiments. Combine that with the fact that 50 % of the probes sent to Mars have failed, and it would explain why there was no research on Mars at all during a long period.

Did you read the URL I provided? Those are Levin’s arguments, not mine.

“Btw, I think Levin is mischaracterizing the later US and EU rover programs. They will go beyond habitability and look for biochemistry.”

Even if you are correct this will be more than 30 years after the original Viking search for biochemistry. What has taken NASA so long to resume the search for life on Mars?

According to Levin the search for life on Mars is no further advanced than it was 32 years ago.

But these are the pretty much the same arguments that you produced on an earlier thread. These experiments are, too broadly, assuming an oxidative (better, redox) reaction as I mentioned earlier. (And you misunderstood apparently.) Which we now know they will see due to the alkaline soil. The only addition Levin proposes is chirality, and as I discussed this isn’t certain to be unambiguous either.

In fact, Phoenix is looking for habitability and understanding of the water cycle, but it is also equipped for looking at signs of bioactivity by means of isotope balances. But AFAIU unfortunately some geological activities mimics life here as well, so again no unambiguous results can be promised.

Btw, I think Levin is mischaracterizing the later US and EU rover programs. They will go beyond habitability and look for biochemistry.

Levin has suggested that a test for chirality would settle the matter definitively, as a chemical reaction would produce random “handedness” (is that right?) while a living response would produce a consistent chirality.

Um, no, that isn’t correct. Biological systems are using chemical reactions, and can produce handedness. Chiral (handed) products results from chiral ingredients, so racemic (both handedness in equal amounts) products results from racemic ingredients.

Also, chiral products will degrade towards racemic, as for example amino acids in proteins “flops” to the other chemical configuration over time.

But most important, it isn’t an unambiguous telltale for life. AFAIU the last decade scientists in medicine, and in lesser degree cell biology, have discovered that cells have a lot of enzymes that converts compounds to and from different chirality. Bacterias but also humans regularly produces compounds of the “wrong” chirality when it is needed, or to detoxify from the wrong chirality for the purpose. And those enzymes are supposedly very old.

Over at Panda’s Thumb you can search and find Gary Hurd’s link collection to abiogenesis material, where the new idea is that life started out racemic, or nearly so, as the prebiotic chemistry probably was. Over time, billions of years perhaps, some life evolved to use chiral pathways when it was advantageous. But as noted this use is modified constantly.

So it is possible that chirality can be used to detect life, perhaps even probable, but not certain. Especially when we discuss non-diversified (early life and/or simple ecologies) life.

Basically, one instrument on Phoenix found a chemical that precludes organic life from having existed on Mars, while another instrument found no trace of that chemical in its samples.

Um, no. Two test with MECA gives (at the time unknown amounts of) perchlorates, one TEGA sample is consistent with a few common perchlorates (detected oxygen but wasn’t looking for chloride) and one TEGA sample is negative.

And perchlorates are apparently naturally occurring compounds on Earth, occurs with chlorides or soils by lightning, uv and ozone.

They are AFAIU no more oxidizing than oxygen and doesn’t usually harm organics in reasonable amounts; some bacterias seems to use them for energy in their metabolism. In fact as they are very soluble they are found in dry environments (like the Atacama desert) or enriched in animals and plants.

But they interfere with iodine uptake so they are both poisonous and used as medicines.

Didn’t this happen many years ago in a completely different experiment with the first lander on Mars?

Both Viking landers did a suit of different experiments. AFAIU the alkalinity of soil discovered by Phoenix can explain these results.

OTOH IIRC some scientists hypothesized at the time that electrostatic action among dusts stirred by Mars thermal winds could generate oxidants (mainly peroxides then), so that hypothesis could come in handy to explain the perchlorates now. But the unblocked uv light combined with the dryness of Mars would be enough, I guess.