[gaukes]

Ceres is one of the more interesting candidates for life in our solar system. Ceres is in the habitable zone for our solar system (although just barely), it's surface temperature is -30 F (eq. to winter in Greenland), and it's detected that the water on the surface is 20% carbon by mass (though that can mean a lot of things).

[QuadrupleA]

Hmm... according to wikipedia Ceres' surface is 110 - 155 Kelvin, or a toasty -262 to -181°F.

https://en.m.wikipedia.org/wiki/Ceres_(dwarf_planet)

Which makes sense, with little to no atmosphere.

If that's correct I'm a little surprised this got voted up to top comment.

[MPSimmons]

The comment you replied to almost definitely relied on the data in the "Geology of Ceres" wikipedia entry[1]. This is from 1991, and was strictly an estimate.

The Dawn probe in 2017[2] got a better measurement, of 110K-155K.

1 - https://en.wikipedia.org/wiki/Geology_of_Ceres 2 - https://sites.nationalacademies.org/cs/groups/ssbsite/docume...

[f_allwein]

in case you’re wondering: That’s between -163,15 and -118,15 °C.

[lopmotr]

You really shouldn't put that 0.15 on the end. The numbers weren't that accurate to begin with so it gives the false impression that those digits mean something.

I hope it doesn't feel like I'm picking on you but I can't help myself saying something because this is a pet peeve of mine. Rounding appropriately is taught in physics class at school but I think most people don't learn that or think it doesn't apply outside of class.

[Sharlin]

Not sure why you were downvoted. The concept of significant digits is pretty important.

[zajio1am]

Or perhaps one should not assume anything about accuracy just from the numeric presentation of the value and when the accuracy is relevant, it should be mentioned explicitly (or looked for in the original source). Numeric presentation is just too vague way to represent such complex issue as accuracy.

Not rounding values after conversion has an advantage that it does not change the meaning of the claim, while rounding requires evaulating assumptions of the original claim to ensure it is done properly.

Also note that rouding of intervals is different than rounding of each of its bound value separately. If the original claim is 'the value is between 110 - 155 K', then proper rounding should be -164 - -119 degC to ensure that the original inverval is inside the new interval so the meaning of the original claim (with its implicit probabilistic assumptions) still holds, just is less accurate.

[HourglassFR]

> Or perhaps one should not assume anything about accuracy just from the numeric presentation of the value and when the accuracy is relevant, it should be mentioned explicitly (or looked for in the original source). Numeric presentation is just too vague way to represent such complex issue as accuracy.

Of course one should assume something about the acccuracy from the number of displayed digits. It's a pretty fundamental concept in physics or even engineering. You can argue that it is just a convention but then again so are numbers in the first place. When writing down a number you will have to make a choice on how many digits to write down (even if its just zeroes), so we might as well use that to convey some meaning. Yes it does not always suffice and so we can use a more elaborate notation when needed, but by default it is a useful convention.

> Not rounding values after conversion has an advantage that it does not change the meaning of the claim, while rounding requires evaulating assumptions of the original claim to ensure it is done properly.

In other words, don't try to understand the claim and just compute. It can make sense in some context but I don't generally think it is the right approach.

[diffeomorphism]

> Or perhaps one should not assume anything about accuracy just from the numeric presentation of the value

One common convention is that the value is written in a way that matches the accuracy. For example, you would never write 73.458 +/- 0.1 because the last digits are meaningless given the accuracy. Similarly, if you measure distances with a tape and round you inputs to the nearest cm, you wouldn't give areas in square mm. In turn, if you give the area in mm^2, then this implies that you think your error bounds are precise enough for this to make sense.

So it is not about readers not "assuming things" but a pretty explicit, though wrong, claim of precision on part of the previous post.

[lopmotr]

We have to assume something about the accuracy otherwise there might as well not be any numbers at all! What if it was +/- 100 K ?

Writing 2 extra decimal places is assuming the original values also have 2 decimal places with zeros in them.

It's reasonable to assume the digits the author gave are correct and there are no other unwritten zeros after them. Even if the scientists really did measure 110.00 - 155.00 K, the author of the source document decided to remove that information and we don't know what it "really" was so we shouldn't guess.

[KMag]

> Writing 2 extra decimal places is assuming the original values also have 2 decimal places with zeros in them.

As long as you have at least one digit of precision, scientific notation is unambiguous as to the number of significant figures.

[alexgmcm]

Is it possible that the conditions in the deep oceans of that world might still be amenable to life - far below the harsh surface conditions?

[astroflask]

Yes, but the (dwarf) planet would then need some mechanism to keep the internal temperatures up, for example Europa and Enceladus have massive planets that keep their interiors warm with tidal forces, or the Pluto-Charon (practically binary) system where both bodies are very near in terms of size/mass and keep themselves warm that way.

Ceres doesn't have any companion to help in that regards, but hints of cryovolcanism have been detected (emission of water vapor on several spots), so at least _some_ internal temperature is driving volcanic processes.

Still, this isn't really my area and you should definitely consider what a planetary scientist has to say, should one chime in to this conversation.

[Chris2048]

I can't see any ref to surface temp on Wikipedia, but this page: https://nineplanets.org/ceres/ says:

> Surface Temperature: -105°C

but also:

> the average surface temperature is about ... minus 38 degrees Celsius

[xxs]

I read that -30F, converted to C (5/9 of -62, like -35) and ughh, no way. That "planet" is too far away.

[walrus01]

Considering that there's organisms that live at ridiculous pressures, with absolutely no sunlight and at the extreme temperatures of deep sea volcanic vents, I would not be surprised at all.

https://en.wikipedia.org/wiki/Hydrothermal_vent

https://en.wikipedia.org/wiki/Hydrothermal_vent_microbial_co...

[crowbahr]

The question is can life arise in such an environment, or only migrate to one.

That's yet to be determined as far as I know: extremophiles have all evolved from less tolerant life forms as far as I'm aware.

[eru]

Though, of course, you might expect to see that, even if life can arise in extreme environments:

It's uncontroversial that life is much denser in more hospitable environments. If the extreme environments are in regular contact with the hospitable environments, and if evolution is sufficiently random, you would expect over time that most organisms anywhere have an ancestor in the hospitable environment.

Even if life can arise in the extreme environment.

[bitreality]

What is the most hospitable environment? A tide pool? Also the most hospitable environment for genesis is likely different from the most hospitable environment for a complex ecosystem.

[Symmetry]

For life without photosynthesis, which takes a while to develop, some place with a lot of free chemical energy because the first replicators will be very inefficient. White and black smokers under the sea are usually put forward as candidates.

[eru]

That's an additional good question that would complicate the simplistic model I suggested in my comment.

[sfvisser]

Live on earth might actually originate from geothermal vents at extreme (for us) conditions.

See the excellent book The Vital Question by Nick Lane.

[guerrilla]

One of the theories I heard recently was that life could arise anywhere there are energy gradients, conditions for forming bubbles and the right substrates. I'm not sure how accepted that is (heard it in a popsci lecture) but it seems plausible.

[eru]

I would still be surprised in the sense that I would gladly give you 100 to 1 odds that we won't find non-earth life on Ceres in the next hundred years.

What are your odds?

[walrus01]

Without a significant drop in the $ per kg cost of putting stuff in low earth orbit, I wouldn't take that bet. I don't think SpaceX starship will be revolutionary enough to put probes in LEO cheap enough.

Once in orbit it's possible to reach things in the asteroid belt entirely through very high efficiency ion/hall effect thruster propulsion, which can have specific impulse as high as 8000.

Any probe capable of drilling or melting into the crust of ceres or Europa or similar will have to be quite large...

[valuearb]

The Space Shuttle payloads to LEO cost $40,000 per pound.

Before SpaceX commercial launch payloads cost $5,000 to $10,000 per pound.

Falcon 9 payloads cost around $1,500 per pound.

Falcon Heavy payloads cost around $1,100 per pound.

Starship payloads will cost between $100 and $500 per pound. It will be able to lift at least 100 tons to orbit. And using in orbit refueling, it will be able to accelerate that 100 ton payload 6.9 km/sec, making landing it on Ceres trivial.

[walrus01]

I am hopeful that Starship will really achieve those figures, but I am also skeptical... I'll believe it when I see it being done.

That's still not cheap enough to do lander/surface manipulation science in the asteroid belt without significant philanthropic or government funding.

At $500/pound, if a Ceres unmanned probe lander with drill/melting apparatus weighs 15000 kg when placed in low earth orbit (before whatever staging/fuel it expends to get to ceres and land), that's still a $16.5 million launch cost before you add the cost of the R&D to build the spacecraft, operate its command and control network, etc.

I will be very pleased and enthusiastic but also shocked if something like that is accomplished for a project budget under $30-40m in the next 20 years.

Not saying it's impossible but we're well within the realm of "big budget" science. Like the operating budgets of one of the smaller (not McMurdo or Amundsen-Scott) permanent research bases in Antarctica, or something like the this:

https://en.wikipedia.org/wiki/Chiky%C5%AB

Big enough that even top tier universities form consortia to collaborate in science projects such as the ALMA array.

[valuearb]

Starship will launch larger probes to Ceres than we’ve sent to Mars, for a lower launch cost. We will do what we’ve done on Mars.

[simonh]

True, but in orbit refuelling means 3 or 4 additional refuelling launches, so now your cost per kg is back up to a few thousand $ per kg again. Still cheap for Ceres though.

[imtringued]

Yeah, orbital refueling doesn't change the rocket equation unless you can manufacture fuel in space. The only benefit is that you don't need a bigger rocket.

[valuearb]

A fully expended Falcon 9 launch costs around $50M. A partially reusable Falcon 9 launch costs around $25M.

Starship will be fully reused. It will launch a 5x larger payload than the partially reusable Falcon 9 at a lower launch cost. So somewhere in the $5M to $20M range.

Starship can be fully refueled in LEO with eight tanker flights, Even at $20m per flight, that costs no more than the Atlas V that just launched perseverance to Mars, only with 40 times more mass.

[eru]

What odds would make you take the bet?

And, perhaps let's talk about a conditional bet that removes the difficulty of space exploration:

The bet pays me X dollars, if human vessels can go to the asteroid belt and not find life. It pays you Y dollars, if we find life. And no payment in either direction, if we can't go to the asteroid belt and don't find life. Say, all limited to the next 100 years.

What's the ratio of X to Y that would make you accept such a bet?

[hyperpallium2]

(not OP) Another clarification: before you said "non-earth life". Panspermia[1] implies Ceres and Earth life are related, so that native Ceres life is hard to distinguish from Earth's (and arguably is the same as Earth life).

1. Backtrapolating exponential evolution finds an origin older than Earth. https://arxiv.org/abs/1304.3381

[eru]

To be more precise: what I meant is life on Ceres that hasn't come accidentally from any of our own probes since eg the start of the 20th century.

I'd be happy to pay up in case of pre-historic panspermia.

[Auracle]

Wouldn’t a nuke work?

[webmaven]

> Wouldn’t a nuke work?

Do you mean NERVA?:

https://en.m.wikipedia.org/wiki/NERVA

[eru]

Please elaborate.

[koheripbal]

Without any volcanism, it's hard to imagine there are hydrothermal vents at all.

[toshk]

I always wondered why we are overly focused on the conditions that created life on earth. Arguably it makes sense to see similar conditions lead to life. But do we really know enough to assume that's only way?

[at_a_remove]

Numerous other ideas exist for alien life, but most of them have their shortcomings. It all boils down to chemical reactions and physics.

Imagine a universe of only helium. No valence electrons would be readily available, so chances are you are not going to see helium molecules. Lithium, sure, as a metal. Continue examining various smaller (and more plentiful elements). Fluorine? Well, only one slot available, so you can make molecules with two atoms, but no chains. If you have two slots open, you can make a chain, but little else. Although try making a chain of oxygen -- even the three-link ozone is not particularly stable. Carbon can have four different bonds going at once, which is pretty crazy, and so you want something with three or four slots available.

But then you say, well, silicon could have four. And it could ... but for the fact that it is so huge by comparison to carbon (that whole other "electron shell") that it rarely has analogues to organic (carbon-based) compounds. Also, it doesn't like to do much until you get it fairly hot. So you climb back up a row and it looks like carbon, nitrogen, boron ... those are going to do your heavy lifting when you need multiple bonds, with hydrogen, oxygen, and the halogens or alkali metals somewhere on the outside. Hence carbon chauvinism. Carbon is something like the fourth most common element in the universe after all.

Then you start talking about solvents -- all of this stuff has to slosh around in something after all, your chemistry experiments take place in liquids -- and the field is a bit wider but dang, water has some crazy properties that make it quite a catch when it comes to solvents.

You've got temperature ranges: down in the single digits of Kelvin you're not going to have much chemistry happening, and up in the thousands of Kelvins even iron boils and then again, no more structure.

Once you start looking for these various "sweet spots" it all comes down to finding a place where you can have liquids (your solvent), solids (for structure), and gases (even if they are dissolved in liquids). Combine that with the more common elements (especially those that are friendly to complex chemistry) and you have something not entirely un-Earthlike.

There's tons of Wikipedia articles on it, but ... the restrictions of chemistry are the bulk of the culprit, I'm afraid.

[henearkr]

You only considered chemistry-based life. Cannot hold it against you of course. But some hard SF writers like Baxter also imagined life based on electromagnetic interactions, nuclear reactions (life in the mantle of a neutron star), fluid vortices and turbulences (life in liquid or gaseous planets), etc. Basically he included a lot of substrates that could be used to implement complexity.

Also, a big drawback of searching only chemistry-based life is that it limits a lot the range of viable temperatures. Would be too slow and simplistic at low temperatures, and a complete uncontrollable chaos at high temperatures.

In particular, finding a brine on an ice dwarf like Ceres is not very exciting, as the temperature is too low, and no interesting chemistry can happen.

Whereas other substrates could be totally fine at different temperature ranges.

[Balgair]

That neutron star story is wild. Hard recommendation to read.

One point I have with Baxter is that his premises are just bananas, but the people acting in them are pretty recognizable. To be fair, if the characters were also nutter-butter, no one would read it, as it wouldn't be a story anymore, just a strangely formatted research paper.

https://en.wikipedia.org/wiki/Flux_(novel)

[gizmo686]

For another life on neutron star: Dragons Egg, Robert L. Forward

[henearkr]

I don't know if you read the other books from the Xeelee series, but the neutron star is probably not even the strangest life form Baxter considered :) I don't want to spoil too much though.

[Balgair]

The Xeelee Sequence is totally crazy.

Not many authors can go the distance from the beginning of the universe, to the end, and then back around again.

They Hyperion Cantos is also good reading. It starts with a re-write of the Canterbury Tales in the far future, and has the pilgrims making their way, not to Canterbury, but to face off with a six-limbed red-eyed spike-covered murder beast that exists outside of time. It ends with hyper-evolved humans and the second-coming facing off against god-like AIs.

Trust, me, it actually works really well.

[thom]

I can never forget reading Titan for the first time. Extremely bleak in many ways but worryingly plausible.

[simonh]

Where I think most of the proposed alternate forms of life in SF fail is they focus on complexity but disregard the need to maintain order. Vortices are a good example, theres plenty of complexity there, but also a huge amount of entropy and no real way to maintain ordered, purposeful changes in structure, or isolation of function. Complexity just isn't enough, so until some of those ideas get a lot more clearly developed, and solve some fundamental issues I just don't find them compelling. Great for fiction and speculation, but not really relevant in real world investigations.

Yes, I know that makes me sound like the boring, hide bound characters in such novels that are incapable of understanding this new amazing form of life, but frankly in the real world those guys would be absolutely right. The protagonists who contact the amazing new life forms just make far too many fundamental errors and intellectual shortcuts to really be credible.

[henearkr]

I agree those are mere plausible ideas with no real foundations, but the aim is to open our imagination to the realm of the plausible. Even those phenomena that are improbable and barely plausible, there are some of them we will encounter, and thanks to the work of sf writers we will not be too much caught off guard.

Specifically for your point on entropy and stability of vortices, I don't disagree totally though I'd like to call your attention on what is known with magnetic skyrmions. They are stable because to change spin the particles would need to overcome huge energy barriers. Then, the only difference with fluid vortices is that in a fluid there is friction that can bring the fluid elements to gradually shed their angular momentum at the contact of other elements with a different momentum. But in superfluid states that you could encounter at very low temperatures (like on some distant planet etc), it is plausible that there would exist analogous energy barriers preventing the fluid elements to directly shed their momentum! And even though, you can of course imagine fluidic circuits and rotational computations, which would have some stability thanks to the superfluid state.

Of course all of that is baseless speculation, but the point of SF is precisely to appreciate the vastness of the world of plausible phenomena...

[Razengan]

"Life" could also be AI machines.

If we seeded a planet with sufficiently advanced robots, that can mine and build and learn and make copies of themselves on their own, and a few centuries later they have a civilization, does it matter what they're made of?

For all intents and purposes, it would be life.

Perhaps at some point we should/will have to stop saying "life" at some point and use terms like "agent" instead, to include disembodied intelligences shaping the universe through their decisions and stuff like that. :)

[fsloth]

I don't think you should confuse life and agency. I fail to see how a bacteria would have any agency.

[bryanrasmussen]

Well then if you found a place with bacteria but nothing advanced you would put in your captain's log that "the fundamental requirements for agency to arise were found, but as yet agency had not been achieved" or some such phrasing.

[ajuc]

> I fail to see how a bacteria would have any agency.

It does stuff on its own. That's agency.

[Razengan]

> I fail to see how a bacteria would have any agency.

Why would it not?

[at_a_remove]

Oh, I remember the convection cell Qax from Baxter, read Dragon's Egg when it came out, or Brin's Sundiver for solar dwellers, or go even further back for the Piers Anthony's OX, even the frozen lattices of light from 2001. I could try speculating on some pretty strange forms of life, and have, but ultimately life -- and as fuzzy as that term is -- might well be construed as interlocking sets of cycles, self-perpetuating at the expense of various resources, always with the second law coming up from behind, waiting to knock it all out of balance, pluck teeth from the gears.

I could talk about how the various conditions at the surface of a neutron star probably cannot support the kind of interactions that would lead to a nuclear pseudo-chemistry (the elements aren't as important so much as the kind of bonds, and therefore structure supported, are, with the other physical properties being less important), but I would like to take a different tack and think about life arising. How would all of those little cycles, circadian down to Krebs, get started?

My intuition? guess? is that just as we are big bags of internalized seawater, life would have hijacked, replicated, and then encapsulated already existing cycles, multiple cycles. Just once cycle wouldn't cut it, probably not even two. I think for us it was all about warm little tidepools, water comes in, then the day-night cycle keeps changing the concentrations. Another tide comes, more water and something, perhaps waste, is washed out. Enough times, enough luck, maybe something sticks, holds something back in case the next splash isn't as big. The next big trick is a membrane, something to isolate the cycles. Separates the outside from the inside. Now there's something to separate.

Overall, though? You're still going to need matter that supports both structure (at least for a membrane, a boundary between in and out) and fluidity (for those cycles). I've thought a lot about what the bare minimum would be, but the Earth chemistry is just a shorthand for "what bonds, and therefore structure, can be maintained?" and "how will it flow?" I am pretty confident in saying it would have to obey Fermi statistics, instead of Bose, because bosons love to play follow the leader, but fermions need to stand out (and apart) enough that they can at least stand. The convection cell entities were interesting to think about but would require an almost unparalleled level of stability and uniformity across large expanses of matter, sort of a large-scale "lab conditions" environment, free of fluctuation and interference, somewhere relatively calm. I have considered something not too far away from that, life existing in an environment where the average energy levels were constant, but the entropy wasn't: life optimized to hunt not for calories but for pockets of order to bolster its own.

Non-chemical life is fun to speculate about but ... I keep coming back to structure and fluidity. It's difficult to find phases of matter that support both that aren't in the chemical domain.

[henearkr]

Nice to see that I speak with a peer SF lover! ^^

I agree, I would be surprised if we discover first alien life in a non-chemical form. Somehow though I would love to be surprised!

There are so many possible environments and substrates, and we cannot think of all of them. The multiplicity of the places where things could happen, and the scale and age of the universe, also increase the possibilities that there are places with the right conditions or stability. The conditions on Earth were kind of lab-grade perfect too! Any nearby supernova, ill-directed solar flare, etc. could have nipped life in the bud. Only the huge number of Earth-like environment in the universe, and the large interval of time allotted, can justify that we have had the chance to arise in these conditions.

PS: also, to be fair, a lot of life forms in Baxter are actually engineered. But our First Contact (or First Observation) could be as well with a "natural" form as with an artifact! And that would not matter that much.

[imhoguy]

Reminds me Solaris written by Lem. https://en.m.wikipedia.org/wiki/Solaris_(novel)

[Johnjonjoan]

This is so non esoteric. I can't remember who said it but I'm reminded of the old saying: "if you can't explain something to a high school student then you don't understand it". You certainly understand it and I certainly appreciate you sharing your understanding in such an accessible way, thanks.

[marcodiego]

I think it was Feynman: https://kottke.org/17/06/if-you-cant-explain-something-in-si...

[jacobkania]

This was fascinating to read, thanks for sharing! I hadn’t thought about how much harder it would be to create life out of other elements due to chemistry. Had previously believed the chances were small that other life would be similar to us, given so many options. You’ve convinced me that it seems more likely that other life would be carbon/water based as well due to those limitations.

[throwaway2048]

Another problem with silicon is that its basic oxide (Silicon Dioxide) is a solid that is non-reactive with virtually everything.

If you assume water based life, there is almost certainly going to be oxides involved, such as how CO2 is involved with earth life.

And I think water based life chemistry is an extremely good bet, because alternative liquids based off of light, common elements are either only liquid at very low temps, (ammonia, methane) extremely reactive ( Hydrogen fluoride, hydrogen sulfide), or both.

Another consideration with silicon is that the earth contains vastly more silicon than it does carbon (in many ways life on earth is fairly carbon starved), yet life based on carbon arose, not silicon.

[thaumasiotes]

> Another problem with silicon is that its basic oxide (Silicon Dioxide) is a solid that is non-reactive with virtually everything.

I was amused once by reading an MSDS for silicon dioxide.

As I presume is required, they do list some hazards of exposure, but if you read the sheets for other substances the contrast is pretty striking. Look at the health effects listed on https://fscimage.fishersci.com/msds/09890.htm :

> Eye: Dust may cause mechanical irritation.

> Skin: Dust may cause mechanical irritation.

> Ingestion: May cause irritation of the digestive tract.

> Inhalation: Dust is irritating to the respiratory tract.

> Chronic: May cause cancer in humans. Prolonged exposure to respirable crystalline quartz may cause delayed lung injury/fibrosis (silicosis).

> NFPA Rating: (estimated) Health: 1; Flammability: 0; Instability: 0

So yeah, as long as you're not inhaling sand, you're fine.

[erik_seaberg]

I'm reminded of

> [Chlorine trifluoride is] also a stronger oxidizing agent than oxygen itself, which also puts it into rare territory. That means that it can potentially go on to “burn” things that you would normally consider already burnt to hell and gone, and a practical consequence of that is that it’ll start roaring reactions with things like bricks and asbestos tile. It’s been used in the semiconductor industry to clean oxides off of surfaces, at which activity it no doubt excels.

—Derek Lowe, “Sand Won’t Save You This Time”

[thaumasiotes]

And from an MSDS for that...

> Hazardous combustion products: None that are more toxic than the product itself.

( https://www.boconline.ie/en/images/chlorine_trifluoride_tcm6... )

It's a fun read.

[raverbashing]

SiO2's "toxicity" is more mechanical than chemical (it's coarse and rough, etc)

But it's pretty much inert chemically (for human levels of chemical reactions)

[Simon_says]

Sure. It's just sand, and it gets everywhere.

[int_19h]

> common elements are either only liquid at very low temps, (ammonia, methane)

But they are very low temps on our scale, which is centered around water.. There are many places, even in our own solar system, where these are liquid all the time, and water is solid all the time.

[throwaway2048]

Sure but the problem is that chemical reactions are MUCH slower at such low temps, perhaps much too slow for life to exist.

[philipswood]

Essay by Isaac Asimov considering viable chemistries for life: "Not as we know it. The chemistry of life"

http://www.bigear.org/CSMO/HTML/CS09/cs09p05.htm

I was surprised to realise (that besides being N author) that he was a professor of biochemistry.

[philipswood]

He ends up with a "list of life chemistries, spanning the temperature range from near red heat down to near absolute zero:

1. fluorosilicone in fluorosilicone 2. fluorocarbon in sulfur 3.*nucleic acid/protein (O) in water 4. nucleic acid/protein (N) in ammonia 5. lipid in methane 6. lipid in hydrogen Of this half dozen, the third only is life-as-we-know-it. Lest you miss it, I've marked it with an asterisk."

[RandyRanderson]

Also water has one of the highest heat capacities [0] of elements that are common so this makes a great solvent that is more resistant to freezing and boiling. For this fact and the ones above, I see it as very unlikely that complex life exists outside any region that doesn't have liquid h20 almost all the time.

[0] https://en.wikipedia.org/wiki/Heat_capacity

[IgorPartola]

Thank you for that write up.

What about non-chemical life. What I mean by that is something like a giant CPU with traces literally the size of freight trains? I recently finished the first Dark Tower book and it’s got me thinking about scale.

[hoseja]

Then you run into speed of light issues. In one nanosecond, that is one 1GHz cycle, light travels only ~30cm.

[IgorPartola]

Hah, good point. The authors of our simulation really put a damper on things, huh?

[frogperson]

This is an outstanding comment. You have made my day.

[qppo]

Are there conditions in the universe where the chemistry required for life can occur with other compounds, that don't exist on earth? For example, extreme temperature, pressure, gravity, electro-magnetic field intensity, etc.

[Dragonai]

Terrific comment. Thank you so much for the excellent explanation!

[renewiltord]

Well, look at it this way: you left your home in the morning for work, went to lunch, went back to work, met a friend for coffee, dropped by the office to pick up your stuff, then got home and found you didn't have your wallet.

You know that, in the past when you lost your wallet, you dropped it somewhere or you left it behind somewhere. However, because you are a free individual and because the universe is full of possibilities (including the event that the quantum froth poofed your wallet away and created an identical one in your hedge), you can do practically anything now in search of your wallet. Do you:

* Retrace your steps to see if your wallet is anywhere along the path

* Call your mother and see if she has your wallet

* Begin a global wallet-hunt in case the wallet was transported to Cuba

Like most people you have an intuitive understanding of what to do: Given limited resources you should allocate them in order of decreasing likelihood of success.

Most things do not lead to life. Our prior on "There is silicon-potassium self-replication on Charon" is pretty low because our prior on "X self-replication" is pretty low for most things.

Try it out. Suggest an alternative and honestly set your priors on it, then condition those priors on the evidence that you have seen on Earth, and the limited evidence from the Moon and Mars. Now look at those posteriors for your alternative and compare it with the kind of life we know. Almost certainly microscopic, but if it isn't, you should publish.

[PaulHoule]

If your definition of habitable is "has liquid water" probably most of the habitable places in the universe are like Ceres, the moons of Saturn, even deep inside Pluto. Between the effects of pressure, geothermal energy, and gravitational tides you find liquid water in those places more than the inner solar system where water gets evaporated and blown away.

(The trouble is that those places don't have sunlight and probably fewer energy sources overall.)

It could be the answer to why we don't meet aliens: they couldn't care less about dry places like the Earth. You could travel the stars hopping comet to comet, but after spending 10,000 years like that you might be comfortable enough in your lifestyle that you wouldn't want to stop at a star. (All contingent on solving the energy problem, either you get lucky and find a lot of uranium or you invent D-D fusion.)

[Symmetry]

My pet theory is that life is pretty common in the universe, it happened on Earth almost as soon as the oceans formed. But photosynthesis, mitochondria, and multi-celularity each took a lot longer and probably represent the biggest barriers to intelligent life.

Plus, as you say, most liquid water is in the deep dark under ice sheets far from the nearest star which makes photosynthesis difficult.

[Chris2048]

> it happened on Earth almost as soon as the oceans formed

But that might have been the final item in a long list of requirements. Maybe life form quickly (on a planetary-scale of quickness) once they are met, but who knows how long that list is.

TBH, I think people fixate on "life" because of some star-trekkian fantasy about aliens, and specifically, other space-faring aliens. There are lots of interesting life-forms on earth that are ignored. We have a lot yet to learn about chemistry, let alone the biochemistry of bacteria, algae, mould. Dolphins and octopi have yet to build boats, let alone spaceships (arguably the monkeys are ahead on this game).

TBH, I'm more interested in what kind of interesting materials and phenomena might exist on other planets. As for life, I think its more interesting to think about what kind of alien environments we can seed with life (and what would form) rather than the moon-shot of actually finding life we are exited about.

Also keep in mind: life or not, it might be more likely we find something else interesting or dangerous. e.g. some kind of adaptable self-replicating enzyme, but made of something more durable than protein (and reproducing in the environmental). Consider the rubber-eating contaminant in https://en.wikipedia.org/wiki/The_Andromeda_Strain

[gus_massa]

You are not so far from the current models. Take a look at https://en.wikipedia.org/wiki/Timeline_of_the_evolutionary_h...

(I think multicelularity of eucaryotes is easier in comparison with the other two steps, it has evolved like 20 times. But in the timeline, it took a long time...)

[ncmncm]

Rocky planets are interesting only to extreme primitives. Once you leave the nest, Oort cloud objects are the most useful. That is where to look for visitors.

[082349872349872]

"But Moooooom, I hate having a few seconds lag to all my friends."

"If all your friends descended to the bottom of a gravity well, you would too? After all, we're not savages."

[freehunter]

Because it’s hard to detect life on other planets. It’s easier if we know what we’re looking for. We know where we came from, so it’s easier to detect.

[gameswithgo]

water and carbon a both uniquely suited to self assembling complex stuff, so its bot crazy to assume those are likely involved

[bjo590]

In addition, we have a large sample of water & carbon based life. We would be able to pick up on more subtle clues if we saw another water & carbon based life-form than if we found a life-form based on other raw materials. Being able to pick up on subtle clues is incredibly important for the search for microorganisms within our solar system, or to have any search of life outside or solar system that doesn't involve looking for signs of intelligence (Scanning for patterns in radio waves, looking for dyson sphere construction, etc).

[BurningFrog]

Everyone agrees that (1) as far as we know, life can arise from a zillion different circumstances, and/but (2) the sane thing is to first look for it in environments similar to the only place we know has life.

[WhompingWindows]

Our biochemistry is based on the most frequently occurring elements in the solar system. It's the most likely biochemistry to use carbon, silicates for instance are much less likely for a number of reasons.

[JohnBooty]

    But do we really know enough to assume that's only way?

I've never heard anybody in the sciences make that assumption. It's just that other biochemistries are speculative at best. Searching for this stuff is time- and resource-intensive, so naturally we look for the sort of life in which we have some expertise.

And to be fair, we are not exclusively looking for Earth-like biological markers. Lots of people looking out for signs of Dyson spheres or other biology-agnostic possible signs of life.

[api]

The question is whether there is a source of energy for that subsurface ocean. If it's geologically dead the entire thing could be uniformly quite cold. Unlike some of the moons of Jupiter and Saturn it's not headed by gravitational tidal effects.

[ojnabieoot]

The idea of multicellular life on Ceres is implausible for the reasons you mentioned, but there could be something like archaebacteria or other extremophiles with very slow metabolisms and which don't reproduce very often. As it's a brine ocean, the water could be chemically "hot" enough that a form of life is sustainable in a bio-geological cycle.

Here's an interesting article exploring the lowest possible temperature for life on earth (which is largely focused on vitrification blocking cellular metabolism but has both theoretical and empirical insights): https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3686811/pdf/pon...

[baggy_trough]

If that's the case why would it be an ocean at all, rather than a block of ice?

[ojnabieoot]

The article said it was a brine ocean, so salinity or some other solute - even at Earth gravity and air pressure, highly saline water can have a freezing point as low as -20C.

[baggy_trough]

The maximum surface temperature on Ceres is -118C. How would you get to -20C without geological heating?

[api]

Pressure? Water unlike most materials expands when it freezes.

[darkerside]

When you apply pressure to ice, does it melt or freeze?

Google says, https://van.physics.illinois.edu/qa/listing.php?id=1593

[loosetypes]

Would evolutionary timelines or cycles be slower in an overall colder planet?

(Thinking of those interactive diagrams for temperature on the kinetic energy of molecules zooming around in closed space)

[clarkmoody]

Did you ever read Dragon's Egg?

It's a speculative hard sci-fi that posits ultra-fast evolution for life on the surface crust of a neutron star!

[loosetypes]

Interesting! Thanks. No I have not.

Although I was previously recommended Rocheworld by a former NASA researcher, with the note that Robert L. Forward made every effort to describe a scientifically plausible double planet.

Incidentally, it looks like Dragon’s Egg is his only work available on Audible. I’ll add it to my list.

[raghava]

> Dragon's Egg

TIL!

Oh, looks like this movie "Evolution" ( https://en.wikipedia.org/wiki/Evolution_(2001_film) ) was also on those lines then!

[rbanffy]

It's an interesting idea, but I find characters developed on the surface of a neutron star will end up being implausibly flat, lacking any depth.

(badum tish)

[clarkmoody]

I see what you did there...

Also, the book does describe a character's apprehension at climbing to the dizzying heights of a few millimeters off the surface.

[rbanffy]

Somehow I don't think they are going to invade other planets anytime soon.

[eru]

Well, at least that seems to be the case on earth. Creatures from the cold deep sea have slower life cycles than creatures in the tropics.

[lostmsu]

Shorter life cycle sounds like faster evolution actually.

[9nGQluzmnq3M]

> the water on the surface is 20% carbon by mass

Sorry, can you explain what you mean by this? Are you using "water" figuratively for all liquid, as opposed to H2O?

[Symmetry]

We conventionally call the Earth's seas "water" despite the fact that they have a lot of dissolved CO2 and fish in them. Presumably Ceres's seas don't have anything like a fish but without microorganisms to scavenge they'll tend to have a lot of carbon containing compounds.

[austincheney]

-30F is too cold for Earth life though. Enceladus is known to have substantial warm salt water.

https://en.m.wikipedia.org/wiki/Extraterrestrial_liquid_wate...

[Tepix]

-30F (-34°C) is the surface temperature. There are probably not many people who believe that Ceres has life on its surface.

[smithza]

What of the lack of atmosphere and lack of active mantle/core? Solar energy has little chance of staying within the system.

[Symmetry]

The potential lack of vulcanic and geological activity now is a big problem. For the first 700 millions years life on Earth depended on chemosynthesis and that's where the energy for that comes from. Presumably there could have been more active geology far in the past, though, possibly implying life that died out.

[bjo590]

Isn't surface temperature a good proxy value of the amount of energy inside the system?

[jayparth]

Well not necessarily. The Martian equator can get as hot as 18C. It doesn't retain the heat (due to no atmosphere) and it gets cold like even a few centimeters off of the surface.

[bjo590]

Wow, I learned something new and can now think about the world more closely to how it really is. Thank you.

[jayparth]

Your comment made me smile :)

[op03]

I had to stand around waiting for a bus in 0 F for a few years of my life. Did not detect any life around that bus stop.

[nkrisc]

You didn't look closely enough. You were surrounded by it.

[618033988749894]

That was one late bus.

[saagarjha]

This is an excellent microcosm of the problems searchers of extraterrestrial intelligence face.

[bzb4]

0 degrees fahrenheit = -17.778 degrees celsius

[orthecreedence]

Are you an android?

[thefounder]

Source?