[sandpaper26]

Disclaimer: I am neither a planetary scientist nor a biologist.

Can someone help me understand the desire to put a DNA sequencer on the Enceladus mission? I haven't previously read anything that suggests DNA as being so fundamental to life that it's a safe assumption exotic moon microbes have it. In fact, discovering that exotic moon microbes have DNA exactly like Earth life would seem like the biggest discovery humanity has yet made.

What am I missing?

[XorNot]

Actually it's exactly that: within the Sol system we know DNA was favored. The lack of evidence of other encoding systems strongly suggests that at the very least, once DNA happens it outcompetes everything else in Earth-like biospheres. Since we're looking for life in Earth-like locales - and Enceladus is targeted for that reason - then it's reasonable to expect we'd find DNA.

The benefit of DNA is it's conclusive: if we find DNA, then life (or an exceptionally bizarre natural process) must be their, and if we grab a sequence then it's high probability we'll be able to figure out what type of life it is due to some Earth-local proteins being basically limited in improvement by physics itself, and heavily conserved - i.e. even totally alien life would be expected to manufacture a close analogue.

Not to mention that if we turn up something totally weird, we can still synthesize it up in a lab to study.

[tsimionescu]

Basically, discovering DNA is sufficient but not necessary to discovering life.

And if we did find DNA (itself a monumental discovery), sequencing it would be the next most important bit of information we could want, since it might allow us to check if there is some relation to life on earth.

[sandpaper26]

But I guess my question is this: we're going to spend $XB to send a probe to a distant moon. Once it lands, we get to ask exactly two questions. Question one is confirm/deny organic life (the microscope). Why is question two's ability to provide a meaningful answer so contingent upon a very specific outcome of question one?

Is this a combo of a) the cost of the second question (i.e. the weight and size of sending the DNA sequencer) is fairly small, b) we're confident enough about question one that putting resources toward question two is worth the opportunity cost of asking a different question, or c) we have no other questions that we can reasonably ask for the same amount of resources?

[Aeronwen]

If you don't ask question two, there's no point in asking question one.

Unless they find the place teeming with life, which nobody expects, it's more likely that anything they find hitched a ride from Earth instead of originated on the planet. So if they're not willing to rule that possibility out, they'll just end up causing decades of speculation and conspiracy theories.

[api]

> The lack of evidence of other encoding systems strongly suggests that at the very least, once DNA happens it outcompetes everything else in Earth-like biospheres.

In 50 years:

The lack of evidence of other languages in use besides JavaScript suggests that at the very least, once JavaScript happens it outcompetes everything else...

I'm just saying it doesn't follow. DNA could be an "average" encoding mechanism or even a poor one. We don't know since we have no other good examples other than contrived lab creations that can't be tested in a real evolutionary scenario since we don't live for millions of years.

DNA could have outcompeted because some lineage of DNA-based organisms acquired an adaptation that led to them outcompeting everything else, even if other encoding mechanisms were superior.

[xen2xen1]

GP isn't saying DNA is the only way, or even the best. They are saying it's a higher probability than anything else we know of. There's value in decisive tests, even if it's improbable.

[formerkrogemp]

It does beg the question; doesn't it? Is there another form of encoding compared to DNA that we may not be aware of and that put our conception of life on its head.

[Qem]

That could prove lithopanspermia. Life with same DNA as found in Earth can either have been ejected from Earth or arrived here from another location. Either possibility would have profound implications.

[lettergram]

> Disclaimer: I am neither a planetary scientist nor a biologist.

I think asking the question is fine, especially if you aren’t these things. Further, you don’t have to be either of those to understand a subject. Kind of silly to assume a biologist would have better insight to your question anyway, most biologists aren’t going to specialize in that area.