None of these "habitable" planets is really plausibly habitable.
In particular, orbiting so close, they are all tidally locked 1:1 to their star, presenting always the same face. If they have any water, it is frozen on the dark side. But they might have no water anyway because they (might!) have no magnetic field to fend off the solar wind that would take away all their hydrogen, as happened to Venus.
Earth has its big moon helping it not get tidally locked, thus still spinning and generating its strong magnetic field. Probably Earth-size planets with a Moon-size moon are vanishingly rare. Dual planets might do better. Or maybe a dual moon of a gas giant, but the radiation belts of the gas giant would be a problem.
So actually-habitable planets must be much, much rarer, among those announced, than astronomy departments' PR crew would have us think. Inside moons of Jupiter and Saturn might even present a better prospect.
That is not to say actually habitable planets must be rare; rather, we can't spot them yet. But our big moon might be important.
Tidal locking doesn't equate to "always presenting the same face".
For example,
> Mercury .. is tidally locked with the Sun in a 3:2 spin–orbit resonance, meaning that relative to the fixed stars, it rotates on its axis exactly three times for every two revolutions it makes around the Sun.
> As seen from the Sun, in a frame of reference that rotates with the orbital motion, it appears to rotate only once every two Mercurian years.
> An observer on Mercury would therefore see only one day every two Mercurian years.
> it rotates on its axis exactly three times for every two revolutions it makes around the Sun.
that doesn't change the argument being made by much. that is still pretty terrible for consistent temperature variations. an extremely long day-night cycle is just about as bad.
(again) Spin–orbit resonance means that "Tidally-locked" doesn't equate to "always presents the same face.
which leads to:
> But it is much farther from the sun than announced planets are from theirs.
a) So?
b) Is it really? I mean sure, in an absolute sense - but what about in an appropriately scaled sense, allowing for the 1/sixth decreased sun mass and the inverse square force relationships, etc.
c) Even so, see a) - How does this alter the fact that tifally locked doesn't equate to "always presents the same face".
To be clear, I'm just highlighting the fragile and dubious nature of your earlier assertion about tidal locking.
If you don't care about "word games", I suggest you stop arguing about "locked" and focus on the actual point, which I rephrased for you. The actual point is about prevalence.
> hundreds of moons
> literally the only body
They are all moons, not planets, and not in different star systems. That's not enough to make conclusive statements about exoplanet spin.
That statistic is more relevant to the word games but I'm not here for word games either. It doesn't matter if "lock" implies 1:1.
Only 1:1 locking is of any interest here. All these exoplanets are certainly so locked. Whether life can arise on such a planet is of course unknown, and will remain so until we find any, but it seems unlikely to me.
Sizes of both objects, speeds, distributions of the chunks coming together, these things have effects. It's not just about being moons but the way you're extrapolating from a single system. And telling everyone to ignore Mercury because you're too right is not helpful.
The point is that these planets orbit extremely close to their star: much closer than Mercury is to the sun, never mind Venus. That is what matters. It has literally nothing to do with any sort of magickal moonityness. Mercury is not special; it is just not locked 1:1. Yet.
Moons in our solar system orbit closer to planets than planets to the sun, so get locked much more quickly. Venus and even Mercury have not quite got there. Earth is in a more complicated arrangement, which helps us avoid it. That might even have been essential for life.
You may read up elsewhere on what determines the tidal forces, friction, and rotational momentum and energy that determine how long it takes to get into a locked state. That would be smarter than word games.
> Mercury is literally the only body in the whole solar system in any sort of more complicated "lock". So, no, it really is about word games.
How would you even begin to demonstrate this is true? There are so many bodies in the solar system, and we're still fairly frequently discovering new minor planet moon-systems..
Dunno man. It's very hard to draw statistical inferences based on a solar stellar system. It would even require significant motivation to argue that the measurements are independent.
The original topic, so cleverly but pointlessly derailed, was the viability of planets we can just barely detect in extremely close orbit around a dim star, in 1:1 tidal lock, with permanently hot and a cold sides, and, likely, no magnetic field. That merited discussion.
I was reading about "eyeball planets", which are possibly suitable for life, and match this description (vaguely, IANAAstrophysicist). Basically, the idea is that a planet of right size and roughly in the right distance to its star is tidally locked in a 1:1 resonance, so one side is always pointing at the star, and one always poiting away.
Now, the perpetual noon point is very hot, and the perpetual midnight point is very cold, but you get a consistent temperature gradient inbetween. Somewhere there, it's about 20 deg C ~all the time.
It's also somewhat tunable. If the planet is closer to the star, perhaps only the perpetual midnight is a happy spot, and the rest too hot. Or maybe the planet is further out, and only the perpetual noon is nice. And so on.
Of course you also make the point about magnetic field requiring rotation, which is not addressed by this, but the temperature side at least maybe is OK.
The water remains frozen on the dark side. Maybe there is so much water that enough sublimates to rain out at the terminator? Still, it is poor pickings.
Habitable also needs a saturn class planet outside, defending against meteorites and comets. Else you can have life on a planet, but it gets "reset" every nthousand years. Lucky us, there have only been 7 to 20 of these events so far.
Mercury and Venus are very near to being tidally locked, despite being thousands of times farther from the sun than the planet cited is from its star. Mars is a good distance off.
Earth got its moon via a nearly, but not quite, fatal collision. Probably most other planets did not.
Ganymede's magnetic field is news to me. I don't think we know exactly what gives a body a magnetic field, or how it is maintained, but rotation seems to be important. Ganymede's is much, much weaker than ours, and some suggest it is a remnant frozen into rock.
> I don't think we know exactly what gives a body a magnetic field, or how it is maintained, but rotation seems to be important.
The magnetic field on Earth is caused by electrical currents flowing in the rotating molten metal of the outer part of our planet’s core. You’re right, rotation is an important factor.
I've long suspected that tidal forces from our moon may be a big factor in keeping the outer core liquid, and thereby keeping our magnetic field active. I have no idea if that's actually true, but if it is, both rotation and a large moon might be requirements for advanced life.
Tidal forces from the sun are remarkably close in magnitude to those from our moon. Their chaotic interaction seems to me to interfere with any big, systematic effect on Earth's rotation.
It seems possible that during certain times in the past, the lengths of the day and month (and year?) were in close enough resonance to accelerate loss of rotation for a while, until the change drove them back out of it .
Yes, but our planet detecting tools can only currently detect planets that are 1. close to their stars and 2. smallish, so that self-selects for tidally locked planets.
And we have gone to the moon, despite it having been impossible for millennia.
And we understand the basic physics of traveling to another star. The only problem is: it's going to take a ridiculous amount of time, and we don't want to do that for a myriad of reasons (money, risk, time), but if we really absolutely wanted to, we could, and there'd be a non-zero chance we'd succeed. Unlike Michael Jordan jumping to the moon.
> So actually-habitable planets must be much, much rarer, among those announced, than astronomy departments' PR crew would have us think
That’s not the conclusion you can draw from that.
With the methods we currently have we can only really spot exoplanets if they are very close to their star and also reasonably big in relation to the star.
That means super-earths close to red dwarfs.
There are very likely many more types of planets, they are just much harder to see from afar.
Certainly it must have, more than that, it helps widening the definition of habitability as slightly too cold planet must be still habitable further out to the sunny side, and slight too hot one must still be habitable deeper into the twilight zone.
Anyway if the water is not all locked up in ice on the dark side. There could be so damn much water that enough sublimates to rain on the hot side or the terminator.
Still, not a place I would start looking for life.
I have read a science fiction story or two set on tidally locked planets, and the humans occupy the slim twilight belt between the hemispheres facing towards and away from the sun, where the temperatures are less extreme.
If it has an atmosphere, though, I imagine its expansion and compression cycle would make it quite stormy.
So I thought this would be big news, so I did some reading. Turns out that in like the past 5-6 years we've gone from "who knows how many habitable zone planets there are" to "we're finding them all freaking over the place!"
Does anyone have a good blog/news site that covers topics like this? Because evidently I'm missing out.
Over the course of the past 2 decades we've gone from "perhaps some day we'll find extra solar planets" to "most if not all stars have planets".
JWST's already found water.
At this point it's no longer a matter of if but when extrasolar life will be confirmed, and with which instrument. Might be JWST, might be WFIRST, might be HabEx.
> At this point it's no longer a matter of if but when extrasolar life will be confirmed
There is absolutely no data to confirm this, simply because no matter what equations or variables you throw around, we have no way of knowing the probability of life. We have only earth, and we still don't fully understand how that all worked out. We do not know what (or if!) any filter is present that prevents complex life. From a philisophical perspective, we'd be much better off as a species that the harder we look, we should hope to find _no_ life: https://nickbostrom.com/extraterrestrial.pdf
But I know I'm an engineer, not a scientist or mathematician. I'm perfectly comfortable with things being true even sans iron clad rigorous proof. If you limit your worldview to only that which has been rigorously proven you miss out on a lot of necessary and interesting truths, I think.
I still have my doubts. I agree it feels true, and yet every "earthlike" planet found so far is nothing like the Earth. How many exoplanets have been found, and how many of those are Earth-size planets with a large moon in the habitable zone of a sun-like star? Because it's entirely possible that all of those are necessary.
Because as inevitable as life may seem, it's also fragile. Practically the entire universe is extremely hostile to it, with the exception of a small layer on the surface of this one planet. Radiation will destroy life, so we need a thick atmosphere and a strong magnetic field, something of the rocky planets in our solar system, only our planet has. The focus is mostly on water and the Goldilocks Zone, but it's entirely possible that there are a lot more requirements to make life possible.
I want to believe there's lots of life out there, but I don't want to be suckered into wishful thinking; evidence does matter.
> I'm perfectly comfortable with things being true even sans iron clad rigorous proof. If you limit your worldview to only that which has been rigorously proven you miss out on a lot of necessary and interesting truths, I think.
A sensible outlook in general. And I frankly think it's true of everybody, even if some people claim otherwise. Most of the human experience is not provable or falsifiable, yet we experience it and believe it.
> How many exoplanets have been found, and how many of those are Earth-size planets with a large moon in the habitable zone of a sun-like star?
I think this is down to how we look at the moment. One of the main ways we find exoplanets is to notice the star dimming with a regular frequency. This gets harder as the orbital time increases, as you need multiple observations of the planet transiting the star to conclude that it's a planet. This means that the vast majority of the exoplanets we know about have relatively short orbital periods, and the characteristics that go with that (e.g. they're close to their stars, therefore less likely to have moons, and if we consider them to be in the 'habitable zone', then their stars are relatively dim).
Actually, the fact that we've found so many exoplanets that fit in the relatively limited criteria that we can detect, suggests to me that there are probably a lot of exoplanets of all kinds, that we're just not as good at detecting yet.
I always go back to people like Drake and Shostak. They seem pretty convinced that "they" are out there, but the problem is that there’s no known way to communicate with them due to distance and time. If there’s a way to solve this problem, please let me know. Sagan and others seemed to think that if we could communicate (a very big if), then we could exchange our knowledge, but how exactly could you do that? The problems appear insurmountable.
I think we'd better hope that we're alone. If creatures like us are common then that's bad new for us, because "life that behaves like humans and exists for millions of years" and "a galaxy that hasn't been completely filled long before now" are mutually-exclusive states. If we have any chance at all of conquering the stars we'll be doing it alone.
Sure, plenty. They just mostly require us to change over time. Maybe sapient species mature and don't feel the need to ever expand, for millions of years. Maybe interstellar travel is so hard nobody ever does it nor do they make machines that do. What worries me, though, is it doesn't seem that impossible. It seems like if humans exist long enough one of us is going to make and launch a Von Neumann probe that eats the entire galaxy. The fact no alien species has makes me think we're far and away more likely to go extinct long before attaining that capability.
I remember a line from a sci-fi novel: "We only consider a species mature when you could put the power to destroy the world into the hands of every single individual with complete confidence that none of them will ever use it." I think we're, eventually, doomed.
I’m with you. But is it reasonable to assume that we can understand each other and share knowledge between the stars? From what I understand, it’s extremely unlikely. After all, we can barely communicate with species other than our own.
By the standards of astrobiology, none of those instruments are capable of detecting life. But they might detect telltale signatures of biosphere in extrasolar atmospheres, which will trigger decades of debate as to whether there is life.
I am not a biologist. I could be entirely wrong in which case please educate me. :)
My understanding was that life would be "detected" by finding chemical signatures in the atmosphere which could not exist at a "steady state" without biological creatures there doing things. Is this what you mean by telltale signatures?
Yes, astrobiologists distinguish between direct detection of life and biosignatures. The latter are things for which we don’t have non-biological explanations at this time, but which we don’t consider adequate evidence by themselves for life.
FWIW we’ve already detected bio signatures for life in the atmosphere of Mars (seasonal methane emissions). And maybe Venus, though that is less clear.
Thanks for this, your phrasing makes the concept more clear.
Can you give a (fictitious as necessary) example of what would constitute "direct detection of life", from an astrobiological perspective? Given our window to the universe is through telescopes I'm having difficulty imagining/distinguishing how to draw the line between "observed data for which we don't have any non-biological explanation" and something even stronger.
Like, does "direct detection of life" only include "we sent something there and found life"?
> we’ve already detected bio signatures for life in the atmosphere of Mars (seasonal methane emissions).
And ~Europa~ Enceladus too, right? ~ISTR seeing some paper about plumes of water vapor, as well as chemistry for which we don't have any non-biological explanation.~ I found it -- I was thinking of in 2017 when H2, CO2 and CH4 were detected at a ratio in thermodynamic disequilibrium .
Edit: I'm guessing "direct detection" in an astrobiological context would be something that builds on "direct detection" in an exoplanet context, a concept I already understand a bit -- friend of mine wrote her thesis on direct detection and imaging of exoplanets 15 years ago. :)
I found and read that before my above comment (and skimmed some of the associated paper[1]) but all that says is direct detection hasn't been attempted since Viking, and that most good signals require in situ or sample return.
It still doesn't answer my question! "astrobiologists distinguish between direct detection of life and biosignatures".
The highest methods in terms of strength of evidence obtainable with remote sensing would be finding "deviations from thermodynamic equilibrium and/or kinetics" of "co-located reductant and oxidant" or "element or isotope fractionations indicative of metabolism". Which sound a whole lot like a detection of a biosignature, which "astrobiologists distinguish" from direct detection . :)
I suspect direct detection in an astrobiological context must mean either "direct, as in we physically touched it" or maybe "a signature found using direct imaging".
Direct observation means, well, observing it directly. Seeing living cells in a microscope. Growing it in a Petri dish. Genetic testing, if it turns out it has DNA or RNA like us.
Within our own solar system that generally means sample return, or sending people with a full biology lab. For an extrasolar planet? I don't think the astrobiology community is of a single mind regarding what should count as direct observation there. We're not sending people or doing sample return for thousands of years. One common opinion I've heard is that seeing an atmospheric spectrograph indicating the presence of biomarkers like oxygen and methane within the habitable zone would be a bio signature, but multi pixel imaging of the planet would be required to claim direct observation. I'm not sure this is a very strong scientific distinction, however.
I'm not an astrobiologist btw, but I used to work at astrobiology.nasa.gov. Small world!
It's a cool idea. Unfortunately getting something out to 550 AU and stopping there would take the better part of a century even with advanced technology. And once you're there, you're really stuck in terms of what you can look at. You can only see what's on the other side of the sun, and with an orbital period of 12800 years, it's not like you're going to sweep out much of the sky in a reasonable timeframe.
If you skip to 14:38 in the video, they describe the solar sails that are supposed to be able to accelerate things to 22 AU/year, which get things to 550AU in 25 years. But yes, you are only going to be able to look at one thing once you get there.
It doesn't necessarily mean that the 0-1 creation of life happened exactly once on Earth (maybe it happened many times but the other lineages died out), but I think it makes this argument likely. We see a near-infinite menagerie of different organisms, from archaea and bacteria to reptiles and mammals, each finding its own niche, yet we don't see, on our own planet, any other blueprint for 0-1 life creation. Everything is DNA/RNA and cells, based on carbon and water, etc. And here we know conditions are just right, and we have studied the Earth like no other alien world.
I'd expect, if the universe is in fact teaming with life, that we would see "aliens" on our own planet. But all we see is descendants of LUCA. It seems to me that either "life" is in fact vanishingly rare, or there's lots of other life forms we don't notice (including on Earth). My gut feeling is on the former.
I am NOT looking forward to the Bell Riots next year.
Being as I lived in SF in the late aughts, me and other friends would joke about the Bell Riots. Then 2016 happened, then 2020 happened, and all of a sudden it's not a very funny joke. :(
Detected by the radial velocity method, measuring the parent star being pulled toward and away from us by a variation of at little as 2-3 meters per second! It always blows my mind that we can measure that.
I know, right? It's mindblowing that we can pass that light through a spectrograph and get the radial velocity just by the infinitesimal doppler shifts. Read about HARPS and the followup projects for more.
I don't understand anything about it, but I think I read that LIGO has been enhanced with a technique involving "squeezed light" which allows some bypassing of heretofore assumed fundamental physical limits through quantum wizardry.
Something else I read about, that doesn't sound like it involves far out voodoo tech to me, that I wish I'd live long enough to see, is putting a probe out far enough and in the right position, to use the Sun's gravity as a telescope lens.
...and (maybe) actually get pictures of extrasolar planets.
I don't know if those pictures would be like Hubble's view of Pluto, or in principle could be much better.
If I could have one wish for something extraterrestrial, that is more achievable, it would be close up pictures of Haumea. Eris and others too, but Haumea most of all.
I care nothing at all for Mars colonies, but the most exciting thing about Starship for me is the hope that maybe combining it with in-orbit refueling could enable quicker travel to the outer solar system and loitering/orbiting instead of flying by at top speed.
There's a funny paradox-like situation that arises in space flight where because of the distances involved/ time taken, it might be better to wait some time for a faster method of flight to develop. Of course, it is up for debate whether there are many more ways of propulsion that are yet to be invented.
15 day orbit, 170 day planetary rotation, that's an interesting one
Sucks for the amount of radiation ofc
Would be interesting to hypothesize of it being a larger mercury like planet than a earth like one
Please some more up to date astro-duders out there, is the James Webb currently capable of direct spectrography of exoplanets? We can do spectrography during the transit I am aware, but direct spectrography, is that possible? Specially when we are talking of an infrared telescope
The wording is a little ambiguous but I read the abstract as talking about the _stellar_ rotation period being ~170d. Not the planet. The star rotating adds a low-frequency signal that interfered with the effect of the planet.
That's sheer insanity. It's mind boggling that at that distance (and therefore footprint on the optical elements) you can directly resolve something even as small as 7x Jupiter.
That's the thing, this rock wont have athmosphere, so close to the host star, it would have been blown away
That's why I mentioned the hypothesized mercury situation, as mercury has got a very thin mantle and its core is VERY outsided, so it has got a very strong magnetic field. This is consequence of likely early solar system crash, Mercury might just be the core remnants of a planetary collision elsewhere
But seriously, these are all too far away for us to reach in any of our lifetimes, barring some insane discovery that breaks all the rules as we know them.
You 'only' need to maintain a steady 1g acceleration for years, rather than seconds.
(What's a mere six orders of magnitude when it comes to physical engineering, anyways? Just spin up a few more jobs on the borg clusters, and if that doesn't work, Moore's law will rescue you in a decade or two...)
If Science Fiction has taught me anything then going to a planet named Wolf {alphanumeric sequence} is a really great idea that won't get most of your crew horribly killed.
Max Wolf catalogued over a thousand high proper motion stars, which tend to be relatively nearby which I guess makes them popular locations for sci-fi.
Followed by an ALM movement a hundred years later. Aliens will rise up complaining of how they were treated in the mines by no other than the earthling colonists.
I am under the impression that Africans did colonize Europe "first" - it is said a group of about 1,000 people came out of Africa about 50,000 to 75,000 years ago and most people outside of sub-Saharan Africa are supposed to be descended mostly from that group.
But it's arbitrary to call them "Africans" now, since they became Europeans and Asians and...
I doubt the intellectual honesty of using the settlement of Europe to excuse subsequent atrocities by Europeans with "Africans do the same thing".
Because all you would be doing is relabeling the same group of people we call Europeans and speculating on what evils they may have committed prior to learning to document it.
The entire concept of equality, and civil rights for all, is a creation of the Wester European Enlightenment with no precedent or counterpart elsewhere.
To put another way, slavery has been present in every human society throughout recorded history. The only ones to have ended it across the board are a) the Roman Empire under Christianity, and b) the UK, France, US, and Brazil (roughly in that order) in the 19th century.
In particular, orbiting so close, they are all tidally locked 1:1 to their star, presenting always the same face. If they have any water, it is frozen on the dark side. But they might have no water anyway because they (might!) have no magnetic field to fend off the solar wind that would take away all their hydrogen, as happened to Venus.
Earth has its big moon helping it not get tidally locked, thus still spinning and generating its strong magnetic field. Probably Earth-size planets with a Moon-size moon are vanishingly rare. Dual planets might do better. Or maybe a dual moon of a gas giant, but the radiation belts of the gas giant would be a problem.
So actually-habitable planets must be much, much rarer, among those announced, than astronomy departments' PR crew would have us think. Inside moons of Jupiter and Saturn might even present a better prospect.
That is not to say actually habitable planets must be rare; rather, we can't spot them yet. But our big moon might be important.