The background for the article is 'tilt erosion time' and the large number of tidally locked planets in the habitable zones of numerous low-mass stars. Many new discovered planets are tidally locked: Kepler-438b, Kepler-442b, K2-3d, K2-155d. It was previously assumed that tidally locked planets would not be habitable. New climate modeling seems to change this view.
The most interesting thing that came to my mind reading this was how different life would be without any distinction between night and day. If the amount of sunlight reaching the planet were consistent at all times, would life (assuming it followed an evolutionary path like earth's) still evolve to have frequent sleep or rest periods?
Rogue planets [0] are also very intriguing. Planets drifting through interstellar space without any star or neighbors.
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.
There are a ton of questions to be raised about how life on such a planet would work. Life on earth is driven by rhythms: a circadian rhythm, tidal rhythms, monthly rhythms, seasonal rhythms - it begs the question whether life is even possible without these built-in cycles.
We have very similar conditions just a few dozens meters under the sea, where sun light doesn't reach. If I remember correctly, creatures that live there still sleep, although their cycles are not linked to 24 hours.
Sleep is the natural state of life, it uses far less energy and we only wake up as a means to procure more energy. On a planet where plants have a constant source of energy to grow the animals may sleep more.
Imagine if such a planet had a small residual rotation left - any civilization on it would be constantly rediscovering millennia-old sites as previously abandoned regions rotated back under the inhabitable region.
This is a beautiful idea, would love to read a novel based on this premise.
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'.
While I agree with most of the other comments that there's little evidence for the argument of the article, it is refreshing to see a different take on the whole "earth-like planets" topic.
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?
You can have all the imagination you want, but it doesn't change the distribution of elements by mass in the universe. The most common are hydrogen, helium, oxygen, carbon, neon, iron, and so on. The likelihood that hydrogen/oxygen in the form of water are the necessary solvent for life is simply a statistical likelihood. They form a polar solvent, which can dissolve many different molecules and move them around. Water is a great medium for life to form in, do you have a different solve to propose? I've heard some try to say liquid methane, but it doesn't have some of the great properties that water does, like solid water being less dense than liquid water (really useful for bodies of water, which keep liquid water underneath a frozen surface).
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.
Carbon-based chemistry isn't the worst requirement to throw in there, since the only plausible analogue - silicon - for example doesn't form stable analogues of the usual amino acids at room-temperature.
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?)
Well, the problem with life that doesn't look like ours is that we'd find it very hard to recognise it as life in the first place, even if oozed to our doorstep and rang the doorbell. So it makes sense to look for habitable planets that could harbour life like ours first- because we're much more likely to recognise them if we can find them.
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?
I taught an undergraduate class on this topic once and was pleased to find that, in the early 1990s, existing textbooks and papers and articles in things like Scientific American had a ton of imagination about non-liquid-water, non-carbon, etc.
One thing I don't get is why nobody ever points out that these are the kinds of planets we're finding because these are the kinds of planets we can find.
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.
There is a third option besides tidal lock and night/day cycle.
Some moons in the outer Solar System have Chaotic Rotation[1]. 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?
Chaotic rotation occurs primarily in bodies that are not spherical. These tend to be smaller, because gravity forces larger bodies into spheres, and would have a thinner atmosphere if any due to the small gravity.
Not saying life is impossible on such a moon, but it would be even weirder than just strange day night suggests.
Two of their most memorable technological milestones might be:
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.
The article explains in length what Eyeball Planets are but gives little arguments why life should be more abundant there compared to other planets apart from a vague number argument.
- 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.
Con:
Flares by the red dwarfs (which are not so rare) could destroy life on these planets
It isn’t that life should be more abundant, simply that Eyeball planets are easier to find. Because they have the capacity to have life (contain a Goldilocks region), that’s where we are most likely to find life first (given current technology). It is a numbers argument, but so is finding alien life in general.
I don't think it made that claim (The HN title appears somewhat incorrect) - just that we are primarily detecting what are likely to be eyeball planets, so if life is out there on any of the planets we are detecting, then it'll most likely be an eyeball planet.
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
Tidally locked planets have a greater range of distances they can be from the central star while having a habitable zone. Non-locked planets need to be at just the right distance.
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.
That's not what it says. Or at least it's not what the article says; the title is a bit dodgy. It's saying that the early habitable zone planets we're currently finding are likely tidally locked, because they're easier to find with current observational techniques.
So, how exactly is evaporation to outer space less of a problem in these red dwarf systems? Shouldn't eyeball planets suffer of that depletion especially?
It has been said that the equators of eyeball planets are the most romantic places in the universe, as they are in a perpetual never ending sunset. Great place for a honeymoon.
Would be interesting to see how a real estate market would develop on a planet like this. My guess:
- 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?
This kind of reminds me of Norwegian mythology where, as far as I can remember, there was an icy world in the North and a fire in the South, and as the fire melted the ice, a thin strip of life began forming.
I wonder whether you'd ever achieve the level of technology required to take advantage of it, though. Mining would be brutally difficult outside the habitable zone.
The article reminds me of another[1] HN article... this one says such a planet might be covered in oceans. I wonder what kind of life develops on an ocean planet? :)
(This is all idle speculation but it's fun to think about)
Life, at least it's origination, requires cycling - this is what allows for the original buildup and release of entropy gradients which follow spacetime trajectories different from the ones of the dead matter. For example you get cells (and especially precells) to get divided by temperature cycling.
Would this eyeball planet structure affect geography? I.e. would the terrain be flatter? Would there be more or less volcanoes? No blanket statements could be made because it would depend more on composition?
[+] [-] nabla9|7 years ago|reply
No snowball on habitable tidally locked planets https://arxiv.org/abs/1705.08904
Stabilizing Cloud Feedback Dramatically Expands the Habitable Zone of Tidally Locked Planets https://arxiv.org/abs/1307.0515
Tidal obliquity evolution of potentially habitable planet s https://arxiv.org/pdf/1101.2156.pdf
[+] [-] fiblye|7 years ago|reply
[+] [-] nnx|7 years ago|reply
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.
https://en.wikipedia.org/wiki/Unihemispheric_slow-wave_sleep
[+] [-] Razengan|7 years ago|reply
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.
[0] https://en.wikipedia.org/wiki/Rogue_planet
[1] http://www.bing.com/images/search?q=Milky+Way+from+Earth
[+] [-] skohan|7 years ago|reply
[+] [-] golergka|7 years ago|reply
[+] [-] flukus|7 years ago|reply
[+] [-] phaedrus|7 years ago|reply
[+] [-] cwkoss|7 years ago|reply
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'.
[+] [-] SmallDeadGuy|7 years ago|reply
[0] https://www.reddit.com/r/WritingPrompts/comments/35mgnn/wp_a...
[+] [-] NegativeLatency|7 years ago|reply
[+] [-] 3chelon|7 years ago|reply
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?
[+] [-] WhompingWindows|7 years ago|reply
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.
[+] [-] XorNot|7 years ago|reply
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?)
[+] [-] YeGoblynQueenne|7 years ago|reply
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?
[+] [-] greglindahl|7 years ago|reply
[+] [-] empath75|7 years ago|reply
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.
[+] [-] Confusion|7 years ago|reply
[+] [-] jobigoud|7 years ago|reply
Some moons in the outer Solar System have Chaotic Rotation[1]. 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?
[1] https://en.wikipedia.org/wiki/Chaotic_rotation
[+] [-] quantumhobbit|7 years ago|reply
Not saying life is impossible on such a moon, but it would be even weirder than just strange day night suggests.
[+] [-] edoloughlin|7 years ago|reply
[+] [-] adrianmonk|7 years ago|reply
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.
[+] [-] some_account|7 years ago|reply
[+] [-] koonsolo|7 years ago|reply
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.
[+] [-] progval|7 years ago|reply
[+] [-] chopin|7 years ago|reply
[+] [-] Tepix|7 years ago|reply
Pro:
- 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.
Con:
Flares by the red dwarfs (which are not so rare) could destroy life on these planets
[+] [-] wffurr|7 years ago|reply
Not necessarily more abundant, just more within reach of our current tools.
[+] [-] mbreese|7 years ago|reply
[+] [-] bencoder|7 years ago|reply
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
[+] [-] barrkel|7 years ago|reply
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.
[+] [-] rsynnott|7 years ago|reply
[+] [-] mar77i|7 years ago|reply
[+] [-] matte_black|7 years ago|reply
[+] [-] cwkoss|7 years ago|reply
- 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?
[+] [-] jaddood|7 years ago|reply
[+] [-] chefandy|7 years ago|reply
[+] [-] macintux|7 years ago|reply
[+] [-] greggarious|7 years ago|reply
(This is all idle speculation but it's fun to think about)
[1] "Group of scientists suggest that octopuses might actually be aliens " https://news.ycombinator.com/item?id=17110874
[+] [-] throwaway1982x|7 years ago|reply
Over geological time period, the zone is likely to suffer unpredictable and novel variability which is not conducive to developing life.
[+] [-] send_computers|7 years ago|reply
[+] [-] jameshart|7 years ago|reply
[+] [-] rsynnott|7 years ago|reply
Earth does that too, though. Ice ages, the odd large impact, etc.
[+] [-] wainstead|7 years ago|reply
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[+] [-] mrhappyunhappy|7 years ago|reply
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[+] [-] madeuptempacct|7 years ago|reply