Under what conditions could a solar system have two or more life-supporting (human life) planets?
We don’t know exactly which conditions must be met for one life-supporting planet just yet, although we could make a pretty good guess.
Assuming that your question relates to why the presence of a nearby second planet might hamper the development of life on a first, I can only guess that the second planet would have to be of similar radial distance from its sun so as not to be too hot or cold, but that this might increase the chance of cataclysmic collision. Plus, the nature of planet-formation from an accretion disc of stardust would likely favour the formation of only one planet at a given distance rather than two distinct planets, in which case the second planet might have to be a captured comet or the like.
If, as seems possible, each planet must further capture a small moon to shield it from other impacts and to create tides, then the probabilities diminish yet further.
I was under the impression that Earth could ‘support’ life because it is at the right distance away from the sun - not too much heat so there will be atmosphere, but not too cold so that the water supply won’t freeze up like Mars.
I’m just wondering if it is possible for a planet further at the back of an imaginary solar system to support life? Could any such conditions occur? (Perhaps something along the line of Jupiter becoming a min-sun?)
It is thought that a star can host multiple life-bearing planets as long as they all orbit within the “habitation zone.” This zone is defined by a minimum and maximum range from the star within which liquid water can exist.
I googled h-z and came up with this link for more info.
I know this may make me sound a bit looney, but here goes anyway.
We don’t know how life started on our planet. And we ONLY know about how life works on our planet.
So, in a galaxy far far away, life could evolve is a completely different matter than it has here. Not carbon-based, not with oxygen-breathing. Neat stuff like that. I think that’d be cool. Then we’d never know what’s needed for life! Drive people batty.
Oh, human-type life? maybe it’d be possible . . . say . . . if there was a planet like Earth, but it had more than one moon, and life came to on one of the moons? Dunno.
I’m not a scientist, tho.
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I can’t watch TV shows or movies where aliens are depicted as humanoids who have taken the same social path that we have. The chances that 1) there’s another life-sustaining planet that 2) developed humanoids who 3) went the same social route as we did MUST be astronomical. I mean, the fact that we went the path we did is a fluke.
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Given a sun with greater energy output than ours, it may be possible for the “habitable zone” to be wide enough for two planets to form within it at different distances from the sun but still be far enough apart for stable orbits. Both would probably be uncomfortable for humans, however, as one would be close to the upper limit of habitable temperature and the other close to the lower limit.
Though it’s not likely to happen naturally (with full planets as opposed to planetisemals), you can have multiple planets sharing the same orbit. Just use the Trojan points.
Right. Plus, as mentioned before, in extrasolar planets you’ll likely have radically different bases for “life” that would have a wider habitable range. After all, we only define the “habitable” zone because, well, we can inhabit it. Life of a different fundamental nature may not need the same biosphere conditions as carbon-water-photosyntesis based life.
(Another multi-world scenario – say that you have a giant planet smack in the middle of the habitable zone, with several very large satellites with their own atmospheres. Those would be “separate worlds”)
What about a double planet? If our moon was significantly larger than it is, near the size of Earth, it could concievably support life. And it would add quite an incentive to our space program.
Problem is, you’d have an interesting time trying to explain how such a stable double planet system would evolve.
I don’t see why not. Consider a river. Rivers form independently in different parts of the world, at different times and in different climates. But, even though each one is unique, they all pretty much look the same.
Development of life could be the same. Even though each race would be unique, they’d all be pretty close and share many attributes.
I can’t remember now - are atmospheres the sine qua non for life that water is considered to be? If not, that could be pretty feasible. However, it wouldn’t be necessary for the gas giant to be in the HZ, because moons around a gas giant have another source of heat: tidal friction.
Back in the Fifties, with what little we knew of planetary conditions at that time, Venus and Mars were both considered as quite possible candidates for life. They are in the “Fertile Zone” but each, as discoveries since have demonstrated, have serious problems relative to life as we know it. (Mars, of course, is not completely ruled out but highly improbable as the site of life.)
But contemplate a thought experiment: swap Venus and Mars, in their present conditions, putting each in the orbit of the other. Significant changes would ensue in each planet’s environmental conditions, and both would move in the direction of more like Earth.
I see no reason why there can’t be more than one life-supporting planet in a solar system. In our own solar system, if Venus’ atmosphere had developed differently, it might have been able to support life. Same for Mars. Of course, we don’t really understand how conditions evolved on those planets and why ours is just right. We generally believe that if we could make the atmospheres of Venus and Mars friendlier, their surfaces could support life.
As for planets in similar orbits, isn’t there some mathematical formula that predicts solar orbits? That formula seems to give credence to the idea that there should have been another rocky planet where the asteroid belt is, but it either could not accrete or was broken apart by some impact.
Can lifeforms be made from chains other than hydro-carbon? I remember my geology professor (a geo-chemist) explaining that (1) not many elements combine as readily as hydrogen and carbon and (2) not many elements are found in the same relative abundance in the universe, which tends to make the chances less than likely. According to him, if life could evolve from other elements, silicon would be a likely candidate. I don’t remember what it would combine with.
Yes, but the formula in the end is so much empirical numerology. It can’t be used to predict anything.
So, Europa?
I think Europan life would be fascinating, but I’ve always wondered if land life is the only life that can evolve sentience. The deep ocean has rocks, chemicals, and the best forges: undersea vents. You can’t do recordkeeping except by etching, though, although that might not be a huge hindrance if a whole species (multiple cultures) evolved that way. And I don’t know if chemistry can be done if you’re constantly in a corrosive and liquid environment.
As for tools, I’m torn. On the one hand, knapping works no matter where you are, and I think the ocean has, at different layers, all of the rocks that would exist at the surface. On the other hand, corrosion would do a number on any simple metal they could create, and metals are the only malleable-yet-strong substance you have until you create plastics. Which they may well not be able to. I know that natural substances can take you a long way, but being tied to natural substances is limiting in important ways. I don’t think spaceflight is possible, for example, with only natural substances.
I think it’s plausible. Mars would just have to be a little bigger and have strong magnetic fields, right? Then you just need a good meteor strike or something to kick some bacteria off of one planet and seed the sister planet. Since life on both planets would be based on the same DNA I could see some similar life forms evolving.
Modern humans haven’t been around that long though and the odds of intelligent humanoids evolving on both planets at the same time is probably pretty unlikely. More likely that the intelligent humanoids would develop to the point they would colonize the other planet themselves.
I’ve thought of that one before, and I suspect it wouldn’t work for Mars. After all, Mars (a smaller world than either Earth or Venus, with a much shallower gravity well) hasn’t been able to hold on to much of an atmosphere even where it is. If you heated it up, that should tend to drive off gases even more, right? So I suspect Mars-in-Venus-orbit might be completely airless.
On the other hand, I do wonder if an Earth or Venus sized world in Mars orbit would do OK: Big enough to hold more atmosphere than Mars (and hence sustain a nice cozy greenhouse effect); but not so close to the Sun (and hot) that it turns into a hell world.
There’s probably all sorts of real-world nasty problems with that scenario (for example, the inhabitable moons would likely be tidally locked to their primary, which would give them odd and unearthly hours of daylight; how important that would be I don’t know)–but it would be really cool. There’s something very neat about the idea. It sounds like the setting of a real-life space opera.
Well, they all look like rivers, yeah, but their individual shapes vary, and no two rivers are exactly alike. And lifeforms (especially multicellular large lifeforms) are a lot more complex than rivers.
Going by the “most rivers appear roughly alike” standard of similarity, the “Cygnan” in the lower right-hand corner of this book cover is arguably “roughly humanoid”. It’s more-or-less bilaterally symmetrical, it has a distinct “head” and appears to have sensory appendages and perhaps respiratory/ingestion orifices at the top, there are manipulative limbs in the middle, and locomotive limbs at the bottom. In fact, just about all of those critters are at least vaguely humanoid (the “Merseian” has a face which is likely far too humanoid to be realistic)–more humanoid than this is, and that is a close relative of ours, compared to any extraterrestrial.
Europa has an 85-hour (3.6 day) orbital period (and thus 85-hour days). I don’t see how that’s so different from our 24-hour day. Especially if a lot of the heat comes from tidal friction and not from the sun. Any other examples of nasty problems you have? Because if that’s the worst one, it doesn’t sound that unlikely.
But what about the Trojan points? (I feel so slighted… 
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