Yes, life could form outside of a solar system. There are huge gas clouds out there and we have little idea what is happening inside of them. The huge nebulae we can see aren’t very dense, but within these vast regions could be all sorts of hot dense gas and dust mixtures where life could develop in ways we have not yet imagined.
That’s (probably) true (although we don’t know enough to say for sure what the lower bound is for an object coalescing on its own). But satellites of a gas giant like Jupiter or maybe Saturn are probably what you’d want for this hypothetical, anyway, and you probably can get Jupiter-like objects coalescing on their own.
As you say, we know very little for certain. But it’s believed that that is, in fact, where life on Earth started. Certainly, photosynthesis wasn’t relevant at first: The rise of photosynthetic organisms was the cause of the greatest mass extinction in the planet’s history.
It’s no different in any significant way than the Sun hurtling through space with its planets in tow. However, using the phrase “in tow” is misleading and probably shouldn’t be used. It gives the impression that the primary object is preceding the secondary objects and that is definitely wrong.
I was going to make the argument that this is a case of special pleading to come up with a “just-so” condition but the paper makes a credible case for how a planet could sustain conditions for liquid water in interstellar space with an atmosphere sufficiently opaque to IR to retain much of the heat generated by interior radioactive decay. (I’ve also been to several lectures by Dr. Stevenson who has done a lot of fundamental work on the atmosphere of Jupiter and Jovian-type gas giants, so this is certainly adjacent to his direct area of research.) It is from 1998 so it is a quarter century out of date from the latest development models in planetology but I don’t see anything immediately wrong with it, so I’ll have to mea culpa to the claim that individual rogue planets could not have liquid water.
I disagree. What we regard as “extremophiles” is based upon our expectation of life in normal terrestrial conditions, but in fact life (or life-like self-organizing non-equilibrium thermodynamic systems) may be capable for forming in even more extreme environments than geothermal vents; essentially anywhere where chemistry can form some kind of stable complex molecules in sufficient density and time has a potential for the formation of life-like systems.
While I wouldn’t discount this entirely, and we have certainly seen the signatures of some amino acids and their their precursors in molecular clouds, but the problem is that these are so diffuse and the energy gradients are so slight that while there are certainly chemical systems they are to distributed for signaling or reproducing stable structures. If there is anything ‘living’ or self-organizing in molecular clouds, it would certainly be based on principles that are nothing like life as we know it, and we probably wouldn’t even be able to recognize it as life.
Stranger
A terrestrial environment certainly helps the evolution of reproducible life forms whatever those might be. If nothing else gravity helps entropic organization of the basic components. But much smaller rocks than rogue moons, maybe no larger than a grain of sand in an environment of sufficiently dense gas and minute dust components might be enough. Life on earth seems so far to be the result of unlikely circumstances already, so life forming in a gas cloud, at least from what we know is an even more remote possibility.
Whether or not we recognize it as life depends on it’s form and functionality. As long as life far different from our concept exists and creates physical patterns or alters it’s own environment would be detectable under the same assumptions of finding life in familiar form. We have to be looking, and close enough to discern the detail.
If you go back a couple billion years to the formation of life on Earth, you’d certainly not survive anywhere on the planet. Nor would most living species. To us, that environment would certainly have been “extreme”.
'Zactly.
What we now label as “extremophiles” are living in environments more similar to the Earth’s surface and shallow waters back when life got going on Earth than the environment we live in today.
As @Chronos alluded to with this bit:
For those unfamiliar with this extinction, this is a good start on the topic:
I pretty sure everyone here knew I was using it as a figure of speech, as in bringing them along with it.
ETA: Dictionary dot com, “In one’s charge or close guidance; along with one”.
I always thought the point of the Miller experiment was that lightning and solar radiation (and the results of radiation from the Earth’s magnetic field) was energetic and active enough to stimulate the mixing and matching of organic compounds in volume suffcient that - theory says - eventually very complex molecules would form in the tidal pools exposed to solar and lighting energy. This also requires a fine-tuned environment warm enough to keep up this activity (liquid water) but not so hot the organic precursor molecules break down. From this we would get evolution of complex replicating molecules, which then collect protective membranes of organic molecules to become life. YMMV.
I have trouble imagining that high-pressure ocean vents, relying on tidal and readioactive decay warming to stay energetic, could create the same energetic moecular recombination - although IANAChemist, if there was a churning with the surface perhaps, considering the extreme level of radiation from the magnetic field of a planet like Jupiter. But… how much of Jupiter’s extreme radiation relies on a feed of particles from the sun?
The Miller experiment showed that lightning and radiation from space could produce complex molecules. It didn’t prove that those were the only things that could do it.
But they did show a level of energetic activity that caused atoms to combine in ways they generally would not have with normal environments. So the question is whether the environments around heat vents would be equally energetic in creating complex molecules.
I assume the point of the Miller experiment was that the electrical discharges created charged atoms that readilycombined with other atoms and molecules, something mere heat would not necessarily provide. Maybe it will. I have no deep undertanding of the chemical processes, but my undertanding is that too much heat breaks apart molecules.
Which is exactly what we need here.
Those perplexed by this discussion like I was, can reference the Cloud Collapse chapter in Wiki’s article on Star formation - Wikipedia . Bolding added
An interstellar cloud of gas will remain in hydrostatic equilibrium as long as the kinetic energy of the gas pressure is in balance with the potential energy of the internal gravitational force. Mathematically this is expressed using the virial theorem, which states that, to maintain equilibrium, the gravitational potential energy must equal twice the internal thermal energy.[17]… The mass above which a cloud will undergo such collapse is called the Jeans mass. The Jeans mass depends on the temperature and density of the cloud, but is typically thousands to tens of thousands of solar masses.[4] During cloud collapse dozens to tens of thousands of stars form more or less simultaneously which is observable in so-called embedded clusters. The end product of a core collapse is an open cluster of stars.[18]
This doesn’t really answer the question, though it provides some context. The kinetic energy of gas pressure must be somehow overcome, and it is substantial relative to gravity. The article also references complications like turbulence, so I won’t rule anything out. I just wanted to get a rough handle on the underlying processes.
Right, nothing, not even stars, forms completely in isolation. They form in clusters. But the clusters are loose enough that they can gradually drift apart, after the stars (or other objects) are formed.
No. The primary producers in the vent food chain produce energy by chemosynthesis of H2S . The whole vent ecosystem depends on that, not marine snow.
Previously, Benthic oceanographers assumed that vent organisms were dependent on marine snow, as deep-sea organisms are. This would leave them dependent on plant life and thus the sun. Some hydrothermal vent organisms do consume this “rain”, but with only such a system, life forms would be sparse. Compared to the surrounding sea floor, however, hydrothermal vent zones have a density of organisms 10,000 to 100,000 times greater.
Neat, thanks!