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jimmydevice t1_iu1iz9t wrote

Reply to comment by svarogteuse in How long do you predict it will take before a probe reaches a habitable exoplanetand actually sends back footage of alien life? by sky_shrimp

Isn't infinity-1 something they only use in improbability mathematics?

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pompanoJ t1_iu2ogr0 wrote

Infinity being an infinite universe.

But in this case it should be whatever fraction of the 100 billion or so stars in the Milky Way have planets that are potentially habitable, instead of the infinity that is the whole universe. We are probably not sending probes to other galaxies for the better part of 5 billion years or so, until Andromeda comes to us.

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svarogteuse t1_iu1je2z wrote

And at this point it look quite improbable that there is anything out there, much less nearby. That could change, the numbers of planets known has gone from 9 to thousands in only half my lifetime, but even with 5,197 known exoplanets as of today we have 1 known with life.

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doc_nano t1_iu2lq5q wrote

I don’t think we can say yet whether it’s probable that any life is out there, or even close by. There could be microbes or even multicellular organisms on Titan and we wouldn’t necessarily know it yet. There could be intelligent non-technological organisms in 25% of the systems within 50 light years for all we know.

However, I agree with your assessment that sending probes returning evidence of life is likely going to take a LONG time, especially if searches in our own solar system come up dry. I’m hopeful that the Starshot or similar ventures will reach the nearest stars sometime in the next few centuries (MAYBE decades), but it could well be millennia before any definitive evidence of life on extrasolar planets is communicated back to us, if ever.

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svarogteuse t1_iu46rae wrote

>I don’t think we can say yet whether it’s probable that any life is out there, or even close by.

The problem with this is its never ending. A hundred years from now with colonies on Mars someone is going to say the same thing about that little niche over there on Mars that hasn't been explored to their satisfaction.

Life on Earth has left no doubts its here. It has produced rocks in volume (limestones), its changed the atmosphere and entire chemical makeup of the surface and oceans. If life isn't thriving across the surface of a world it wont last in geologic terms. Life isn't going to hold on under some rock for any length of time, being localized like that is to fragile. And there is no evidence that anything on Mars or Titan isn't the result of normal non-life initiated chemical reactions. As much as we want it to be life isn't common.

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doc_nano t1_iu4bh2m wrote

>The problem with this is its never ending. A hundred years from now with colonies on Mars someone is going to say the same thing about that little niche over there on Mars that hasn't been explored to their satisfaction.

That's right. However, the more we explore a planet without uncovering any signs of life, the more confidently we can say there probably isn't life there. I'm personally not holding my breath for finding evidence of life on Mars or any other body in our solar system for that matter. There's no evidence yet that I find very convincing.

But it's a large leap from that to claiming with any certainty that there IS no life on any body in our solar system other than Earth. It may seem like we've explored our solar system quite a bit, but we really haven't - not in the detail that would be required to rule out the existence of microbes. To use a common analogy, that's like taking a bucket of water out of a large lake, looking at it with a magnifying glass, and claiming there's no fish living there.

>As much as we want it to be life isn't common.

I'd agree that life as we know it is definitely not common, in the sense that it probably occurs on a small minority of all rocky bodies (most of which don't have any water or atmosphere, so it's hard to imagine any life arising or existing for any geological length of time there). We don't yet know exactly how uncommon it is. Does it arise on 25% of terrestrial planets or moons with liquid water in the habitable zone? 1%? 0.00001% Does it arise in 25% of star systems with terrestrial planets in the habitable zone? 1%? 0.00001%? We don't have sufficient information to rule out any of these possibilities, as far as I know. We can't even analyze the atmospheres, much less the surfaces and soil chemistries, of any extrasolar planets in much detail (or at all, in the case of soil chemistries).

I understand the motivation to tentatively conclude in the negative, so as not to be disappointed. I have a Ph.D. in chemistry and it's still difficult for me to imagine a probable series of steps to life on Earth, so it wouldn't surprise me if less than 1 in 1000 star systems had life. But it's ok (and indeed more accurate) to say that we just don't know how common life is yet.

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