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A study has found that the two outermost TRAPPIST-1 exoplanets are the most likely to be able to retain their atmospheres:
The last thing the planets around the red dwarf star TRAPPIST-1 need is abundant sunshine. Active eruptions and flares from the star would wreak havoc on the rocky planets in orbit. But fortunately, the outer planets might be safe from this barrage of high-energy space weather.
According to a new study in the Proceedings of the National Academy of the Sciences [DOI: 10.1073/pnas.1708010115] [DX], the outer planets of the system could cling on to their atmospheres. This finding is despite previous studies showing that TRAPPIST-1 might be so active that it blows away planetary atmospheres.
[...] The new results show that while all seven planets could retain their atmosphere, the more likely scenario is that the outermost two, -1g and -1h, have the best odds (and -1e and -1f have a weaker chance.)
This could be resolved by JWST observations.
(Score: 0) by Anonymous Coward on Wednesday January 03 2018, @04:37PM (14 children)
I suspect while simple life is common, complex life is rare. Look at all the things that had to go right on Earth. If we didn't have a big moon, Earth would often be stuck with one side (edge) facing the sun and the other freezing in the dark. So far it appears big moons around rocky planets are fairly rare (although the jury is still out on that).
And if Jupiter were not where it is, asteroids would keep "dinosauring" life too often to settle.
If a rocky planet is too big, volcanos keep wiping things out, and if too small, it can't hold an atmosphere, and may lose its magnetism. We have a roughly even mix of rocky areas and ocean. Most likely it would be almost all one or the other: an even mix is a fluke balancing act. The even mix gave time for animals to evolve in our ocean before land was ready for complex habitation. Too much has to go right.
The best we'll find in our neighborhood stars would likely be no more than sponge-like critters. No green Orion babes, sorry.
(Score: 2) by takyon on Wednesday January 03 2018, @04:49PM (1 child)
To be fair, finding any evidence of extraterrestrial life (even if it is just microbial) outside the solar system would be an amazing scientific achievement. And this could be done by finding evidence of vegetation, oxygen-rich atmospheres, etc.
Gas giants are not uncommon, and their masses can be pretty tremendous before they are considered brown dwarfs. Although maybe a brown dwarf orbiting a star could fulfill that same "vacuum cleaner role"?
What is less clear is whether or not they are in the right spot to perform that role. But we may be biased towards discovering gas giants that are closer to their stars and thus easier to detect using radial velocity or transit methods.
Determining how habitable red dwarf systems are is pretty important since there are so many of them.
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(Score: 4, Interesting) by Immerman on Wednesday January 03 2018, @05:57PM
> we may be biased towards discovering gas giants that are closer to their stars
Exactly, and no maybe about it. If we were watching our solar system from Alpha Centauri we'd probably still have no idea that Jupiter existed* - it hasn't even completed three orbits in the time we've been hunting for exoplanets, and you want to observe several orbits to have any sort of confidence in your discovery. Currently the exoplanet with the longest year we've discovered is Kepler 421-b*, at a paltry 704 days, vs. Jupiter's 4,333 days.
* even assuming Alpha Centauri was looking at our system edge-on, instead of the reality of being at a steep angle which makes detection far more challenging.
(Score: 3, Interesting) by Immerman on Wednesday January 03 2018, @05:38PM (11 children)
Without the moon, the Earth still wouldn't be tidally locked - not even Mercury has tidally locked yet, and it experiences radically greater tidal forces. Meanwhile the the moon is slowing the Earth's rotation as well, and probably far faster than the sun alone would have. What the moon *does* contribute is tidal heating, but at a guess, that's potentially dwarfed by the thermal effects of greenhouse gasses in the atmosphere.
Even if a planet *were* tidally locked, that wouldn't necessarily be a problem, so long as thermal mixing between light and dark hemispheres was sufficient to keep the atmosphere from freezing out. And there would be a serious energy gradient to power such mixing. Dense greenhouse atmospheres could also help immensely - for example Venus's solar day lasts about 117 Earth days, and yet the surface of Venus is basically all at the same constant temperature night and day, from pole to pole.
I've never heard any claim that large planets would have inherently greater vulcanism - they'd certainly take longer to cool initially, but once they reached the point that life becomes feasible, they'd also maintain that level a lot longer. Small sizes do likely correlate with losing their magnetic field faster though, as they will cool faster, and it seems likely that a liquid core is important to maintaining a magnetic field. However, while a magenetic field certainly *helps* to maintain an atmosphere, it's not absolutely necessary - witness again Venus, which has the densest atmosphere of the inner planets, despite having no internally generated magnetic field (instead, it has an induced magnetic field created by the interaction of the solar wind with its atmosphere)
As for the mix of land and ocean - I see no reason to assume that it contributed to the evolution of complex life, which was thriving in Earth's oceans long before anything ventured onto land. Admittedly though an undersea existence would potentially put a damper on some branches of technological development, as fire was an important enabling technology for early tool-making, metallurgy, optics, etc. Undersea volcanic vents might be harnessed for similar purposes, but would likely pose a greater challenge.
(Score: 0) by Anonymous Coward on Wednesday January 03 2018, @07:20PM (10 children)
I didn't mean tidally locked, but having a stable "tilt". Without the moon, the tilt would change wildly, sometimes facing a single pole toward the sun for millions of years: freezing one polar half and cooking the other. More info:
https://www.space.com/4333-wobbles-mars-produced-40-ice-ages.html [space.com]
I believe current models predict it, but I have no formal surveys of planetary geologists to present.
That might be true, but the current batch wouldn't had have enough time to reach that state yet. Remember, the first 2 generations of stars were metal-poor, meaning less planets and less minerally-diverse planets.
Carbon-dioxide, which is probably not an animal-friendly gas. (True, we don't know all combinations of animal-friendly conditions.)
I already gave it: a place for animals to start and evolve *before* land was ready. And it provides diversity of environments, which is probably helpful to general evolution. Narrow environments tend to hard-wire in instincts such that big brains are not needed, being they are metabolically costly. Hard-wired instincts are "cheaper" if the environment is stable or "boring".
(Score: 2) by Immerman on Wednesday January 03 2018, @08:42PM (9 children)
Ah yes, wobbling could indeed be an issue - but you're not going to get a single pole pointed at the sun for even a fraction of a year. The more the pole is inclined the more extreme the seasons, but over the course of any given year (or century) the pole will be relatively motionless, while the orbit of the planet carries it around the sun normally, so that each pole spends half the year being closer to the sun.
As for planets cooling, our third-generation sun was born a few billion years into the third-generation stellar forming period. We're newcomers to the party, and there's been plenty of time for planets around early third-gen stars to have been coolling for longer than our sun has existed.
Nothing wrong with carbon dioxide - it's mildly acidic, but no worse than plenty of other things we're subjected to. The biggest problem with CO2 for Earth life is that we're designed to use CO2 concentration as a stand-in for oxygen concentration, and high concentrations cause all sorts of secondary reactions related to that (we can't detect oxygen levels directly, which is why nitrogen leaks are so dangerous - you feel just fine until moments before you drop unconscious from asphyxiation)
That's a reason for *oceans* to be important - which I acknowledged. Land though clearly contributes far less - we can see a wide range of problem-solving-smart ocean dwellers that are easily as intelligent as any non-primates on land. The thing that gives primates an edge is a mutation that prevents neuron size from scaling up with body size (as is normal for all cells), so that primates with bigger brains have more neurons and are thus more intelligent, rather than just having bigger neurons, as its the case with basically all other animals. (Also the reason that brain/body size ratios make a decent approximation of intelligence between species, but only among non-primates). Such a mutation would likely be beneficial to almost any creature that evolved it - we just got lucky. And there's no particular reason to assume it would even be necessary for life elsewhere, as there's no inherent reason to assume alien life would have the same limitations to begin with.
(Score: 2) by takyon on Wednesday January 03 2018, @09:17PM (1 child)
There are more neurons in elephant brains [wikipedia.org] than human [wikipedia.org] (though they are far from dumb).
I think the bigger factors are brain structures devoted to complex cognition as opposed to say, movement. Also differences in neuron types, where bigger can in fact be better. For example, a study in which larger human astrocytes were grown in mice brains [newscientist.com]:
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(Score: 2) by Immerman on Wednesday January 03 2018, @09:50PM
Hmm, I didn't realize that. Interesting - certainly they are extremely intelligent creatures whose intelligence we are only beginning to seriously research.
And certainly brain structure and neuron types play an important role as well in determining how that processing power gets put to work. I suppose what non-scaling neurons really allowed was for a creature as intelligent as a human, at a scale considerably smaller than an elephant.
(Score: 0) by Anonymous Coward on Wednesday January 03 2018, @10:57PM (6 children)
Okay, I was incorrect about the duration of "darkness". But it does seem a strange that Earth has such a big moon and that according to current theories/studies, moons that large for mid-sized planets are relatively rare. The fact that it's unlikely and that it does have season-dampening properties doesn't strike me as a mere coincidence.
I don't see why you consider it a mere mutation that lasts for millions of years. Primates have complex social structures and complex environments, and big brains are adaptations for that. Octopuses are relatively intelligent on "physical" issues, but don't have complex social structures, relatively speaking, and thus have relatively small brains. It appears it took a combination of complex environment (or niche) and complex social structures to bring about primates.
(By some accounts, Neanderthals were possibly smarter than humans from a pure reasoning standpoint, but probably less social. Similarly, dogs are dumber than wolves from a pure "mechanical" reasoning standpoint, but are better at working with humans. Humans and dogs are thus "socially domesticated": we rely more on teamwork and specialization.)
If a mutation that simple were all that were needed, then something like the Anomalocaris could have relatively quickly grown into an intelligent being early in animal history. But it didn't because brains are metabolic expensive, and hard-wiring behavior allows them to be smaller. It takes special circumstances to make big brains justify their expense. The larger variety of niches and environments, the more likely the special circumstances are to be triggered. Our combo of oceans and land does that.
(Score: 2) by takyon on Wednesday January 03 2018, @11:35PM
https://en.wikipedia.org/wiki/TRAPPIST-1#Moons [wikipedia.org]
If TRAPPIST-1 doesn't have many large moons, that can be blamed on the red dwarf star and the relative proximity of the known planets to the star. Even if there are undetected planets much further away from the star, they are well out of the "habitable" zone.
Earth does have an unusually large moon in this solar system, but we still haven't gotten a single confirmed exomoon detection.
The Kepler mission is starting to teach us what types of exoplanets seem typical (although biases exist), but we don't have any sample of large moons other than the ones in our own solar system (a sample which could be incomplete if a Planet Nine is lurking out there).
We have observed many (presumed) rocky exoplanets more massive than Earth, which means greater Hill spheres (compared to 1 Earth mass placed at the same orbit).
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(Score: 2) by Immerman on Thursday January 04 2018, @12:14AM (4 children)
It is indeed uncommon according to current theories (though it should be noted those theories are based on a data set far too small to actually draw meaningful conclusions from), and should indeed have a wobble-stabilizing effect. But where's the coincidence? If life is actually common, then a large moon might be incidental - we really just don't know. The real question is how much of an influence that would actually have on the evolution of life. Probably not much for organisms clustered around undersea vents, which potentially carried life all the way from organic chemistry well into the realm of complex organisms. As things colonized nearer the surface though, would harsh seasons wipe out life, or drive it towards greater adaptability? Even plankton could migrate easily enough on ocean currents to remain viable in harsh seasons, especially near the equator where climate would be relatively stable. And where plankton grow, ecosystems can grow atop them. Meanwhile, any organism that could handle being frozen solid through the winter would have a head start on the migrants come spring. Plenty of organisms can handle that here on Earth - they'd probably have a major evolutionary edge on a world with extreme seasons.
There is nothing "mere" about mutation - it's the mechanism which makes evolution possible. Every step from single celled organism to modern life has been a mutation that provided some benefit that outweighed any associated disadvantage. Clearly the "neuron size doesn't scale" mutation did, sufficient that every modern primate is descended from one distant ancestor that had the relevant transcription error in his genes. It wouldn't have instantly made a huge difference, but it shifted the balance point on intelligence-versus-metabolic-cost, which made something like us far more likely to arise: social tool-users are everywhere on the planet, most never became anything like us.
Certainly the other side of the equation, natural selection, is also every bit as important - it's what turns a bunch of random noise into a multitude of different species resplendent enough that some insist on believing in a conscious designer. It's both together - imperfect self-replication, and competition for limited resources, that allows for evolution.
(Score: 0) by Anonymous Coward on Thursday January 04 2018, @06:51AM (3 children)
But those tend to be designed for hardiness, not complex behavior.
Like I stated, large/powerful brains are metabolically expensive. Unless the size pays for itself, such mutations would fade from the gene pool rather quickly. Large brains on Earth tend to be associated with complex social structures plus complex environments or niches. Therefore, the big brains here are probably a gradual adaptation to circumstances rather than a single or few random mutations in terms of "suddenly big".
Examples? It's more than just "using tools". Some birds use sticks etc. as hooks to get food in tight spots, but they are not otherwise generally "smart".
(Score: 2) by Immerman on Thursday January 04 2018, @03:22PM (2 children)
Quite true about hardiness - here. Put them on a planet where that hardiness gives them a substantial advantage over everything else, and they'll likely end up being the progenitors of a large portion of the global population, rather than niche players relegated to the fringes.
I said nothing about anything becoming "suddenly big". And absolutely big brains are expensive, which is probably why we don't see them often. But the non-scaling mutation didn't give us big brains - it just improved the cost/benefit ratio so that later mutations for bigger brains were less expensive than they otherwise would have been. Plenty of primates out there with tiny walnut brains - they have the "cheap big brains" mutation as well, they just don't get as much use of it. For the first individual to develop it, it probably actually made their brain smaller(cheaper) at the same intelligence, or smarter at the same size, or somewhere in between. Something that gave it enough of an advantage that it and its descendants could out-compete the rest of the troop.
Parrots can make tools (e.g. tearing of a splinter of wood and intentionally bending the end into a hook) Ravens can make tools and solve multi-step brain teasers to get at appealing treats (I.e. solve puzzle A to get piece to solve B,etc,etc,etc, to solve F and get treat). Dolphins make bubble-nets for fishing among many other tools, and can quickly grasp how to use more sophisticated tools when presented with them in the lab. What *exactly* do you mean by smart? It's actually a really slippery term when you try to precisely define it. One of the big things modern biology is making us realize is that humans aren't actually all that special intellectually - we have "more" brains, and as they say, quantity is it's own quality, but we don't appear to actually have any particular intellectual traits beyond that that set us apart.
My point is that lots of other social, tool-using species have bumped up against the "bigger brains aren't worth it" line - what really set us apart and let us advance so much further was that incremental increases in our brain size came at a lower metabolic cost, so that the "bigger brains aren't worth it" line was drawn at a much more intelligent point - far enough that we were able to develop more sophisticated technology and communicate it between generations - fire, stone tools, etc. At which point we became something more than just smart animals, we could build upon the intellectual accomplishments of our ancestors, which made bigger brains even more valuable, since the insights of the elders today could continue to benefit their descendants in perpetuity.
(Score: 0) by Anonymous Coward on Thursday January 04 2018, @04:53PM (1 child)
I'm not sure what you mean. A human brain takes roughly 12% of our energy. It's not more efficient per neuron than say a lizard brain.
And birds who have to dig stubborn bugs out of trees and tight spots to feed themselves indeed have decent physical tool problem solving abilities. But they don't have a sophisticated social network, and are thus more or less tool savants.
(Score: 2) by Immerman on Thursday January 04 2018, @10:07PM
Hmm, you seem to be correct - I had been operating under the assumption that calories/gram remained relatively constant, but it does appear that calories/neuron is the more constant guide. (still not constant, but nothing compared to the variation in neuron density between species.)
That being the case, I can think of two other advantages that smaller neurons bestow:
1) Brain size at birth - humans are already born "prematurely" compared to other primates so that our skulls can fit through the birth canal, without small neurons it would require much more major skeletal modifications to allow birthing of big-brained babies.
2) Signal transmission delays are diminished - at ~3x the weight of a human brain, an elephant brain with the same amount of neurons as our own would average ~44% longer transmission times between neurons.
It might also make complex neural structures lest costly to make.1
Anyway, I need to reexamine some my my assumptions. Thanks.