No snowball on habitable tidally locked planets
Stabilizing Cloud Feedback Dramatically Expands the Habitable Zone of Tidally Locked Planets
Tidal obliquity evolution of potentially habitable planet
And this modeling was confirmed to be accurate... how, exactly?
This strikes me as a classic case of goosing the model until it says what you want it to say, and then getting in the news. We have no reason to believe these models. We have no reason to believe prior models, either. We have no reason to have any confidence in our ability to model a tidally locked planet, of unknown and arbitrary chemistry, around an unknown star, for unknown periods of time, with unknown orbital characteristics across geological time, with zero data points. We particularly have no reason to believe in any estimates of how long such a system could last; it doesn't seem to do life much good if there's a place for it to exist for a couple of million years, followed by freezing. The simulation is almost certainly unstable here; very small changes in the stability of this configuration will have massive changes to the result over even a few million years.
There's also more to life than just a comfortable temperature. Life is possible on Earth in part because we have a moon and plate tectonics keeping this stirred up, so some of our vital nutrients don't just sequester themselves somewhere chemically convenient after a couple of million years and then hang out there for the rest of the planet's existence. Do these types of planets have a solution for that? We have no idea. (One advantage of the Earthlike planets is that we do in fact have an idea... we know it's at least possible once.)
What is your level of expertise or knowledge of planetary astrophysics and climate modeling?
This does not require extensive study.
Furthermore, as a bona fide, credentialed expert in computer science, I observe with the full power of my credentials that other fields frequently abuse modeling to get into the news, and that as I said, this shows all the hallmarks of being one of those. There is a profound, mathematical way in which models simply spit back out at you what you put in. This profound mathematical understanding seems to be broadly lacking, and it makes people grant wildly excessive credence to unverified models. As just a single for instance, I expect you have no idea how many models they ran that produced lifeless planets until they finally found one that yielded a result conducive to life. Given the almost-certainty that these systems are deeply, deeply unstable, I expect it is almost certainly the case that they had a large number of runs where the system simply ran away in one direction or another.
Edit: I challenge the downmodders to produce a single data point about an eyeball planet in a habitable zone and demonstrate a model that correctly represents it. "We have to have data before we can verify a model" is not some sort of wild anti-scientific statement; the belief that a model can be trusted without validation is the wildly anti-scientific position!
If some of you are mistaking this for a position on the climate debate, note that we do have data for Earth's climate. Not as much as we might like (could always use more!), but it's certainly much greater than zero. You can literally get more than zero data just by walking outside and observing the temperature right where you are. This point has nothing to do with the climate debate on Earth.
3d General circulation models and basic energy balance models are verified against range of temperatures, pressures, and atmospheric conditions in the Earth, Mars, Jupiter and Venus. The same model used for exoplanets is used to model paleo-Mars, paleo-Venus, and Titan. If the model is somehow completely wrong outside known limits, so is the parent model that is used in the Earth Climate change studies. The models work just fine at this level of required accuracy. You put parameters that describe the Earth, Mars or Venus into the and you get good description of atmosphere and climate in Venus and Mars that matches observations.
We don't have to model specific planets to get interesting information. In generally the interest is to model different categories of the planets and discover how their environments vary when we vary the parameters. It's possible to say something generic about tidally locked planets and their climate. This is what these simulations do.
GISS modelE GCM
ROCKE-3D version of GISS modelE GCM
Besides the examples you mention, research groups are now doing data assimilation for Mars (https://www2.physics.ox.ac.uk/research/geophysical-fluid-dyn... https://agupubs.onlinelibrary.wiley.com/doi/full/10.1002/201...).
Other groups are testing and improving models for Jupiter and Saturn, as you mention, based on various remote sensing observations. (For Saturn, see: https://theoryofclimate.sciencesconf.org/conference/theoryof...).
All of these cases have allowed modelers to observationally test their models and model physics against non-Earth conditions. This work has been going on for a decade now, but it somehow has not reached the technically-aware audience.
The case of tidally-locked planets is another step beyond the above solar-system planets. Thank you for the references you supplied, in your original comment, on GCMs for this case.
I enjoy modeling, and I think it's useful, interesting as well as respectable work. But a little humility would in science is always a good things.
Regardless, it's more useful to point to particular areas of uncertainty than to point to a general miasma of uncertainty around climate modeling as though nothing can be learned. It doesn't really move any conversations forward.
Just because we can't predict when an individual hurricane will occur doesn't mean that we can't predict "hurricane season".
edit: Apparently it's not even certain whether the Sun will engulf the Earth or not!
That's alright. I'm a credentialed expert in computer science myself and I'm also always right about everything, including entire scientific fields I know next to nothing about.
If you understand how computers work, you understand how everything that uses computers works!
She said, "That's like SlimFast."
Since it was marketed for tech guys, it was a tech discovery.
Somewhere in an alternative universe, there must be an astronomers' forum talking crap on developers because Heartbleed and Spectre show they all misunderstood Goedel's theorem, and believe me, I totally know what I'm talking about, I use computer every day.
But apparently the same is not valid for complex fields like astrophysics, spacephysics or astronomy.
Btw tidal locking can cause tectonic activity, as in the case of the Jovian moons.
Things are finally settling down to the point where models match independent data, e.g. the recent research into sea level changes as measured by satellite.
So now, finally, we can start making informed policy choices based on cost benefit analysis. (Actually, no, who am I kidding - Greens worldwide will keep hating on industry and capitalism, and everyone else will keep pretending AGW isn't real. But at least we could start forming rational policies if we wanted.)
Back on topic, to assume that we can make any kind of predictions about the climate of life bearing exoplanets seems like the height of arrogance given the state of the art in climate modelling.
Predicting whether life might exist on a planet can probably tolerate ±10% temperature accuracy. There's no reason to believe that smart geophysicists can't achieve that level of accuracy.
My point, perhaps snarkily made, was that we are only now getting the hang of this, after decades of work.
Unless I'm missing something, we're not going to be approaching anything like 10% error bars for planets for which we have far less data.
At the risk of misunderstanding “eyeball planet”, you’re living on the most obvious example.
Elsewhere in Sol, Mars is in the “optimistic” habitable zone (I think that means “it would be if only it had been massive enough to retain an atmosphere”).
Earth climate models you already believe in so I won’t bother to name.
Can anyone else tell me the accuracy of The Ames Mars General Circulation Mode?
You should read the articles on this website please.
There is such a gigantic massive amount of information we dont know.
Any words spoken about how life is created should be met with the same skepticism we have toward religion. We require evidence and the scientific method, a simulation made my students who need to be correct for a PhD isnt evidence.
I don't understand this anger about having untestable models. How would science progress without having theoretical possibilities before testable possibilities?
Every challenge he puts forth requires at best high school level critical thinking skills.
By his own "logic", we can't even be sure they're tidally locked (because how did we determine that? Modeling!) Which I mean, is technically true because hey welcome to science where confidence intervals are a thing.
Surely the specialist knowledge comes after the general knowledge? If a Nobel prize winning Astrophysicist says "there are exoplanets where you can make a perpetual motion machine" you would not let him get away with that?
The guy further up was just saying that there are general things about modelling (a very broad topic that reaches across all of science) that don't add up.
Ultimately, reasoning about observations are authoritative, not credentials.
You're demonstrating exactly why general knowledge isn't enough to analyze specialized concepts! Your rhetorical question may seem to the layman to be a witty retort but it just demonstrates ignorance of the topic at hand.
In the case of your perpetual motion machine example, anyone with even slightly specialized knowledge of (astro)physics would know that there are no fundamental phenomena like the conservation of energy that prevent life on an eyeball planet, unlike with a perpetual motion machine. This is the rhetorical equivalent of comparing a Mount Everest expedition to intergalactic teleportation.
> The guy further up was just saying that there are general things about modelling (a very broad topic that reaches across all of science) that don't add up.
No, he was just saying that there are general things about how modelling is used. He didn't say a single concrete thing about the article itself and proceeded to demonstrate vast ignorance wrt this specific subfield of scientific modelling.
He did say something concrete, which is that we have no observations to compare the model to.
Which is wrong. That's my point. You wouldn't know that without some specialized knowledge in astrophysics and how the models are developed and verified.
The people with the highest credibility tells the rest how it is, and we don't question it. Now it's magic eyeball planets, next year it's spinning discs with Santa in the middle.
As long as credentials are impressive, it all checks out doesn't it...
Maybe most creatures on such planets would evolve towards unihemispheric sleep, as some Earth species did (eg. dolphins).
Unihemispheric slow-wave sleep (USWS) is sleep with one half of the brain while the other half remains alert.
Light/dark is only one factor in sleep, there are others.
It's also hard to know of the infinitely many evolutionary twists and turns lifeforms in the Universe may take, how many of those pathways involve something like sleep - especially on planets without a diurnal cycle.
Anything and everything is a wild guess based on a sample of one where extraterrestrial life is concerned.
Although they may never get sunlight, I suspect the view in their sky would be spectacular indeed (like ours when away from cities and light pollution, but even better.)
Maybe all that unfiltered starlight would be enough to coat the planet in a unique twilight all around, or maybe life there would specialize in other senses besides sight.
The planet may generate sufficient heat from its core and most of the life there might live underground, or there might be some other heat-providing geochemical processes on the surface.
The thermal vents from volcanic activity seem to be reasonably well insulated from cyclic activities at the surface. They would likely only see variation from cycles with much longer scales, such as the 26 ky axial precession cycle, the 41 ky axial tilt cycle, the 100 ky orbital eccentricity cycle, the 112 ky apsidal precession cycle, the 300-500 My tectonic supercontinent cycle, etc--the ones that can change climate and geology, rather than just weather.
The vent dwellers might get an inkling if an ice age has been going on the surface for a while, or if runaway greenhouse effect is boiling off the ocean surface.
The sort of forced nomadism from "only" having ~1000 years before a location becomes uninhabitable would make for some interesting dynamics. Real estate at the leading edge would be very valuable, potentially with some kind of homesteading dynamic for claiming the land (as nobody has lived there for thousands of years). Also value of land would depreciate over time because it would have an 'expiration date'.
Also, the polar territories would only have to worry about precession, and their land might have a longer expiration date.
But soon the Bright comes, melting the glacier which holds the lake back from the Dark. They can't cross, it's now full of chunks of ice, and they have to get through hostile neighboring lands.
Call it Sunrise.
I am regularly shocked by how little imagination commentators in the popular science press seem to have on this subject. Even highly-respected scientists frequently refer to "requirements" for extra-terrestrial life such as carbon-based chemistry, the requirement for water, a mechanism of natural selection, etc, etc. (Actually I consider the last one, posited by Dawkins, to be probably the closest to the truth.)
I guess it's simply the anthropic principle at work, but even the nature we see on our own planet far surpasses our imagination often (especially at the microbial level), so why should we be placing any constraints on the rest of the universe?
Additionally, carbon itself forms stable amino acids, stable nucleic acids, and does so not only on Earth but even in celestial samples we have taken from outside Earth origin. So, would you rather a non-scientific writer leave the confines of sound science to speculate wildly? As a scientist myself, I'd rather they confine themselves to the most likely and sensible scenarios the majority of the time, since their purpose is to inform and inspire the public. Some small amount of speculation is fine, but education should be first and foremost.
Good answer though.
From there it probably gets a lot more divergent. I'd also bet that cells and something like DNA is pretty common wherever carbon-based life is found, but my understanding is that the exact way DNA codes for proteins is pretty arbitrary, and the fact that all life on Earth more-or-less uses the same coding scheme is an artifact of the common origin of life rather than because it matters.
Body plans and the details of multi-cellular life are probably going to be wildly divergent, with some caveats. For instance, eyeballs evolved multiple times on Earth, so it would be surprising if eyeballs didn't evolve pretty often elsewhere.
(Incidentally, if aliens are made of proteins, sugars/starches and fats, that means that whatever they look like, we can probably eat 'em, barring the usual toxins and allergens.)
So, you ask, what about Silicon? Silicon also has 4 valence electrons, so it ought to be a nice substitute, right?
The problem is that Silicon is in the next row down.. so it's more massive and it's electron cloud takes up more room. So you still only have 4- connectors, but it's a larger element.
There's clearly an advantage into being able to form precise and small molecules. Carbon, with it's small size and 4 valence electrons, is a clear choice for a backbone.
I'm a complete layman, but how does that play out in planets with gravity force significantly stronger or weaker than Earth? Woul that skew which elements make the best building blocks?
Silicon is basically impossible as a building block for life. It forms bonds that are too strong, meaning it requires much more energy to fuel life processes and reducing the rate of chance collisions which lowers the prospects for abiogenesis.
Carbon is the only realistic choice; it is the only element abundant enough with the right balance of stability and versatility.
Now it would be reasonable to say "well what about extreme environments" but we are specifically looking for planets with temperatures and "ambient energies" similar to ours - so it's reasonable to think that whatever chemistry is there probably has to follow Earth to a large degree.
If instead we were talking about high-pressure hot Jupiters or something, then it gets more interesting - but that's going to be something so different we're unlikely to recognize it at all (what consciousness does sentient life which evolved in a gas-environment have?)
That bond stability had to play a gigantic role over the last billion years of evolution.
And knowing that life like ours has already developed on a planet like ours, it makes sense that there will be others like it out there, so we might as well look for them first.
I'm not saying that ET life can't be very different to ours, or develop in conditions radically different to ours- but it makes sense to start searching at the most likely place for the most likely thing, no?
It may be the most likely to be easily recognized but not necessarily the most prevalent. You have two variables to balance: (a) likelihood that the planet you're looking at contains life and (b) likelihood that you'll know it when you see it.
If you can increase (a) significantly then it may not matter if (b) is very low or not
We'd have no way of identifying an earth-sized planet at an earth-sized distance from a sun-sized, star, as far as I know.
There could be a huge amount of exactly earth like planets out there that we have no way of finding. In fact -- all the sun-sized stars we've looked at that we can't find planets at all around, might be ones with solar systems just like our own.
But I am not an astronomer, would love to see some data on this.
Some moons in the outer Solar System have Chaotic Rotation. These bodies don't have a fixed rotation axis or period.
There could still be such a Moon orbiting a planet in the habitable zone, or even a small planet in a belt like structure orbiting close to a red dwarf.
I wonder what lifeforms could evolve when the amount of light/energy received is unpredictable and varies constantly?
Not saying life is impossible on such a moon, but it would be even weirder than just strange day night suggests.
Thousands of years this sounds realistic, but remember the scale of things is in billions of years.
1. First crossing of the hot side, passing through the point where "sun" is directly overhead. (Having the sun directly overhead would probably seem very profound and unusual to them.)
2. First crossing of the cold side, passing through the opposite point.
Both would have unique challenges. Crossing the hot side would require an amazing ability to keep cool. You can keep warm by burning stuff and using lots of insulation, but how do you do the opposite?
Crossing the cold side would have temperature challenges and also very difficult navigation because of the continuous darkness. Maybe there would be moon(s) and stars for some light, though.
In both cases, I wouldn't be surprised if the first crossing had to wait until the invention of the airplane. You definitely aren't doing it by sea the first time like we did here on Earth.
When I was 18, a group of friends and me were going to create a computer game based on this tidally locked concept. The story went as follows: An explosion would occur in a huge spaceship close to such a planet. Both parts of this ship would make an emergency landing on this planet. One part on the cold ice side, one on the hot desert side. Both teams would work their way towards the habitable ring, in a true real-time-strategy (Command & Conquer) fashion.
Needles to say, the game never went further than this concept phase.
Although we did visit a small local game developer here in Belgium called Larian, to get a feel of running a game development company (must be back in 1998). Larian is now known for the critically acclaimed Divinity: Original Sin.
- Red dwarfs are by far the most common type of star in the Milky Way, at least in the neighbourhood of the Sun
- Red dwarfs exist for a long time (longer than ten billion years) which gives life a long time to spring into existence (or start via panspermia) and evolve
- Planets in the habitable zone of a red dwarf are tidally locked ("eyeball planets") due to their small distance to the star
So there is very likely to be a huge number of these types of planets with stable conditions over a long period of time.
Flares by the red dwarfs (which are not so rare) could destroy life on these planets
As a layperson, I'm curious how "bad" those flares are. Is it in the realm of possibility that life that develops on these planets could "hide" from these flares when they happen, or evolve defenses against them for when they happen? Or is it more "turn the surface into lava" kinds of events?
You could have life that's 100m deep underwater, or living in protected structures (caves, etc). Life could evolve more protections against UV (e.g. some kind of carapace that the organism resides within).
Maybe the hard part is figuring out a way to use UV-heavy light to generate energy.
Not necessarily more abundant, just more within reach of our current tools.
It's a bit circular and not really saying anything useful, but at least it's not claiming what the HN title (nor your criticism) is saying
If a planet is closer to its star, it's more likely to be tidally locked. It can however also be in a spin-orbit resonance higher than 1:1.
As to which kind of planet we'll find life on, depends on whether tidally locked planets with habitable zones are more frequent than non-tidally locked planets in a habitable orbit. I don't know that we know the numbers here.
We are learning that there are liquid oceans all over our solar system so I'd argue that the classic concept of a habitable zone is outdated because it doesn't take them into account.
It specifically means "the light from the planets sun is in the range to support surface-level life".
If a distant moon in our solar system has a liquid ocean that A) doesn't mean it's water or anything else sane and B) that habitable zones are poorly defined.
Liquid oceans generated by orbital- or geothermal activity aren't covered in the habitable zone definition and aren't very useful as they usually require a parent body to provide energy to heat the ocean (jupiter for example) but just not enough to boil it off the moon.
- Side of planet closest to sun would be great for solar, agriculture.
- Equator would be great for retail, recreation - constant sunset makes everything look beautiful.
- Just further than the equator might be an idea place for housing - it's always dark, but short commute to light.
- Further away from the equator would be cold, which could be useful for heavy industry (particularly exothermic processes)
I wonder how a society's 'clock' would work without the day/night cycle. Would people coalesce around a certain common "day" cycle or would everyone be on different schedules so society operates in shifts?
Going away from the center, properties would get cheaper due to harsher conditions, the poorest of people living in increasingly hotter and colder conditions. But they would also live closer to the factories that lie toward the poles of the planet, making for faster commutes.
Somewhere in the very hottest and coldest extremes, would be a good place to keep prisons.
I wonder how much benefit, if any, data centers get from operating in colder regions.
(This is all idle speculation but it's fun to think about)
 "Group of scientists suggest that octopuses might actually be aliens " https://news.ycombinator.com/item?id=17110874
Over geological time period, the zone is likely to suffer unpredictable and novel variability which is not conducive to developing life.
Earth does that too, though. Ice ages, the odd large impact, etc.
"Life finds a way" - but if the temperature suddenly jumps 100 degrees because your goldilocks zone librated into the sun, then you ain't got much capacity to evolve protection from that.
As an earthling this is probably the first thing you think about when you read about Mars - too hot for life in the day, too cold for life at night. But that makes way too many assumptions relative to _human_ life. It assumes nothing could be rigid enough to adapt to day and night extremes greater than Earth's.
It seems to me the greatest challenge to thinking about potential life outside this planet is being mentally bound to the constraints of life on this planet.
I always felt the same way about astronomers linking liquid water with life but then again where do you start if you don't use the only known instances of life in the universe as a template? Maybe it happens that there's a viable evolutionary path for sentient Nitrogen clouds but how would we know that?
Furthermore it doesn't sound too absurd that the very complex chemical constructs necessary for life would have a greater chance to stabilize in less extreme environments with a smaller temperature amplitude. Especially if you're looking for complex life and not merely microbes (which tend to be a lot more resilient).
Most likely because looking at extremophiles on Earth, you just need somewhat stable energy gradient and you'll find some life that draws energy from that gradient using weird chemistry.
Hardest to find for us because most of our chemistry research is geared towards carbon compounds around 20deg C, not sulfur compounds around 500deg C that dissolve most of our equipment in minutes.
Disregarding the possibility of life elsewhere that couldn't possible survive on Earth discounts most of the planets we know about.
So if survival of those life-forms depends on gravity, pressure or chemistry then we definitely should not rule out places where those are different than on earth, in fact that is to be expected. But temperature is a very important factor and the make-up of the star itself is also very important.
So it makes sense to check the likely places first before spending time and effort on much more unlikely places.
Some of these organisms also have novel ways of acquiring energy, so it seems like research like this is probably our best near bet for understanding how life can thrive in extreme conditions.
I'm having a hard time finding all the people stodgily insisting that only life exactly like Earth's is possible through the hordes of people screaming about how it might not be. Everybody already knows that life might not be exactly like Earth life. Any illusions to the contrary have been shattered by Earth life itself and the concrete existence of extremophiles, which are themselves already not what most people imagined "Earth life" to be.
>That image may very well be completely off-base. There is good reason to think that the first potentially life-bearing worlds that are now being detected around other stars...
"may be", "Good reason to think". Not exactly ex-cathedra pronouncements from on high.
Now of course if we consider the much, much smaller subset of planets we may hope to actually observe then of course it might not be so likely.
I also think the initial point of the article in insightful, although rather obvious: since the planets we're currently looking for are not Earth-like (because we're currently unable to detect planets such as Earth in other solar systems) it means that if we find something it'll probably be very different than what we're used to. Now of course the author goes on to flip that around by saying "since we're looking for planets that are not like earth we're going to find this and that" which is obviously a bit presumptuous. Still, fantasizing about alien worlds is something I always greatly enjoy so I'll allow it.