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Comment by mFixman | Hacker News Reader

20 years ago it would have been unthinkable to find water in any other planet in the solar system.

Mark my words: in 20 years, we'll find extremely simple proto-bacterial life in Mars and in many other planets.

I fully expect us to find something like a bacterium somewhere else. They might even be very common anywhere where there's hydrothermal activity. Prokaryotes seem to have evolved _twice_ on earth (archaea and bacteria), albeit from some common proto-cell thing. So there's some chemiosmotic 'recipe' which can make them.

What I don't expect is anything like a eukaryote and certainly not like multicelular life. I think that kind of life is either vanishingly rare or non-existent elsewhere.

There was almost 3 billion years of life on this planet before eukaryotes arrived, and they arrived only once and in a form likely almost identical to what we see today. So it's really really 'flukey' and not something that 'just happens' in some necessary teleological fashion.

Nick Lane gets into this in his book "The Vital Question" -- it's quite convincing. And maybe depressing if you grew up on sci-fi like myself.

Ya my feeling at this point is that there is likely primitive life on every planet having liquid water, which means at least one moon around every gas giant, which means nearly every star which has gas giants (not even counting planets in habitable zones). So that part of the Drake equation is covered, but intelligent life could still be rare.

I just imagine the odds of a planet-sized petri dish not evolving life in billions of years, and I certainly wouldn't take that bet!

I don't think liquid water is sufficient by itself - first, aside from water, life as we know it requires some source of energy. Since surface water seems much less common than subsurface water, that means life will need to get energy from some sort of chemical process similar to the bacteria that live around hydrothermal vents. That means those vents need to exist in the first place, and need to expel sufficient chemicals for energy creation.

There also may need to be some source of extremely high bursts of energy such as lightning, to create the compounds that are precursors to life (amino acids, RNA, etc.), and those bursts must also not be so frequent/widespread that they kill all life.

You have to keep in mind we're teetering on the edge of an exponential explosion in knowledge. What's been done in decades with all of our rovers and probes on Mars could have been accomplished in a matter of days by a single human on the planet. That's not an exaggeration. For instance we're coming up on Curiosity 6th year on Mars in a couple of weeks. It's traveled, in this entire time, a bit less than 13.3 miles. There's an ongoing odometer available here [1]. And it's had some major instrumentation errors (such as with its drill) that a human could have trivially repaired on site.

Only question is how long is it going to take us to get those feet on the planet. From there? I'd expect major discoveries will be a matter of months.

[1] - http://curiosityrover.com/tracking/drivelog.html

Or even on moons. There are several moons that have a non-zero chance of having life on them.

I'm betting on Europa. Lovely little moon, so many mysteries. Can't wait to see what we uncover from there.

Heck, even if it ends up being completely lifeless, IMO Europa is still one of the most exciting bodies in the solar system in terms of future potential - Between abundant energy from the Jupiter-Io flux tube, methane fuel from Titan, hydrogen and helium from Jupiter herself, and water from Europa, colonization of the Jupiter system may well be the key to the outer solar system, and potentially even interstellar efforts. More immediately, it could be an essential stepping stone to enable largescale harvesting of the Jupiter Trojans.

Even if you'll never see a Jupiter-rise, I for one love the idea of living on Europa.

I know HN is not one for jokes, but colonizing 'Europa' seems like a hilarious irony in name.

Isn't the issue with exploring Europa that Jupiter throws a stupid amount of radiation around itself, so spending any time on its surface(or close proximity) is actually a very very bad idea for human life? Sure, beneath the ice you'd be safe as you can be - but you need to get there and then drill through the ice first.

I doubt we'll see it in many other planets. Mars is by far the most likely planet in our solar system to harbor life, outside of Earth obviously. If you talk of moons, however, then we get into many, many more candidates that could potentially harbor some kind of microbe or multi-cellular water creature.

We have already established that microbes live on the exterior of the ISS. They may have come from Earth originally but it does show that life can exist in conditions that we humans consider to be absolutely inhospitable.

Isn't life thought to have started in "conditions that we humans consider to be absolutely inhospitable".

Yes, but to quote the annoyingly semi-reasonable creationist Ken Ham: “We weren’t there. We didn’t observe it.” (Note: I am not a creationist, I do agree with the logic of that argument, but I also see no scientific basis for any religious origin story of life to have more scientific basis than others).

We have recreated the conditions that predate life and found that organic molecules were formed, but we’ve never observed the leap from organic molecules to organic life. So the best we can do barring the invention of a time machine is look for life elsewhere from Earth to try to fill in the blanks.

It's more interesting to think about the thing that we know in spite “We weren’t there. We didn’t observe it.” For example:

How were the continents a long time ago. Like Pangaea and before. Yes, we have good understanding of the continents before Pangaea.

How did bird evolve? [spoiler alert] They are small dinosaurs!

How is the center of the Sun? [I'm not sure that this falls in the original meaning of “We weren’t there. We didn’t observe it.”, but it is included in the literal meaning.] In some books of 100 years ago you can find weird explanations about the origin of the energy of the Sun.

Why the time of and orbit of Pluto is 3/2 of the time of the orbit of Neptune? Was this also true in the origin of the Solar system?

Where does the Moon comes from? [Weird story, hope you already know it.]

Most of this things were discovered in the last 100 years. I'm missing a few that were discovered before and are so mixed in the popular culture that it is impossible to imagine that thy were unknown before.

We still don't know how the first life form appeared, and I think we are cueless for now. We don't even know if they[we?] used ADN, ARN or something else. [ARN looks nice]. Did they get the energy "eating" organic molecules, from some H2, or something else? Protein-first or membrane-first?

We will never observe a leap from organic molecules to organic life, because (probably) there is no leap and because it (probably) takes too much time. The plan is to understand a few key steps, reduce the huge leap to a dozen of small steps, perhaps with substeps. Hopefully try to simulate the substeps in the laboratory, experimentally or by computer, and be sure that the path is correct enough. I hope that one century is enough, but perhaps I'm too optimistic.

The answer to “We weren’t there. We didn’t observe it.” is: We don't know ... for now, but it never stopped us in past to know a few amazing thing, so we are optimistic.

You see a man lying still on the ground, blood pooling around his body, and a woman standing close by gripping a knife with bloody hands. What happened? “We weren’t there. We didn’t observe it.”

She tried to save his life by removing the knife, then she went in to shock? Probably not the explanation you had in mind. This is not a good metaphor.

You see? You are still able to make theories based on what you know and causality, and we can debate about which theories are most likely to be true. Not directly observing something is the beginning of theorizing. We don't just give up on knowing.

That only works because humans have killed each other, not to mention animals, many times in the past, so all of us are familiar with the process. We're yet to observe any instance of abiogenesis at all, anywhere.

We don't merely make predictions based on patterns we currently observe. We also make predictions and reason about the past based on reason, causality, and other theories we can demonstrate to be true.

Do microbes really live there, or just survive in a stasis?

https://mars.jpl.nasa.gov/msp98/why.html

Not exactly true. Water on Mars has been thinkable for quite some time:

https://en.m.wikipedia.org/wiki/Chronology_of_discoveries_of...

Yeah well, in the 19th century it was believed there were supposed to be canals up there :).

And there has been speculation about water on Jupiter's moons since at least the 1960's. Probably longer.

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