Nitpicking, I know, but to call it "Planet Ceres" in the title is more than a bit wrong. This is a dwarf planet at best and is also often classified as a really big asteroid (the only one in the asteroid belt that's rounded by its own gravity). If even the much larger Pluto can't get the "Planet" title, Ceres hardly deserves to be called that in a headline from a major newspaper.
I suppose the question is whether "dwarf" is a modifier to "planet" or whether "dwarf planet" is a compound word that cannot be split without losing meaning.
I would lean toward the former -- if there was not room in the headline for "Dwarf planet Ceres", referring to it as "Planet Ceres" still adds information and clarifies helpfully. "Ceres" may not be familiar enough to most readers for them to instantly think, "Oh, they must be talking about the largest asteroid/eighth largest known dwarf planet", but adding "planet" makes it clear that we're talking about space stuff.
Here's a Euler diagram on planets, dwarf planets, minor planets, so on and so forth from Wikipedia [1].
Alan Stern, who coined the term "dwarf planet," initially wanted it to be under the umbrella of planet as a distinct subtype. [2]
The International Astronomical Union (IAU), however, believed that what we call a dwarf planet — it was referred to as a planetoid — should not be considered a type of planet.
The IAU later held a session where they decided to use the term dwarf planets in place of planetoids, however they decided that a dwarf planet is not a type of planet.
It's semantically inconsistent, but that's where we stand right now per the IAU.
I don't know what the criteria are for defining a planet (and I know that there is a great deal of controversy), but "rounded by its own gravity" seems like a good dividing line to me.
That is half of the criteria the IAU decided defined a planet. The problem is that our moon is rounded by its own gravity and would be classified as a planet under that just criterion.
The other half is meant to exclude moons from the 'planet' definition: the body must 'clear' the neighborhood around its orbit. The Earth is in the same solar orbit as our moon but is much more massive, thus our moon doesn't count as a planet. Pluto doesn't meet this criterion because its orbit intersects with Neptune's orbit, and Neptune is much more massive.
Probably depends on your age. Did you grow up with Pluto being a planet? Having to learn about it in all levels of schooling as a planet? Seeing images of all the planets and Pluto is included?
Or did you grow up afterwards and learn from elementary school that Pluto is not a planet so people who still insist that Pluto is a planet seem anachronistic?
It would be like Hydrogen being removed from the periodic table and being told that from now on Hydrogen is no longer considered an element. Would you still try to say that you feel that Hydrogen really is an element, even though you are wrong and Hydrogen is not an element and never should have been included on the Periodic Table in the first place?
> Did you grow up with Pluto being a planet? Having to learn about it in all levels of schooling as a planet? Seeing images of all the planets and Pluto is included?
Yup, grew up with all of those things.
And when they discovered more Plutoids - some even bigger than Pluto - when I was in high school, I loved watching science change as more information came in. Because that's what science does.
I love that we now have better definitions to more accurately describe bodies orbiting a star, and Pluto is definitely not a planet the same way the 8 planets are.
Pluto was a planet when I learned about it in school. I also learned that it was the one that was discovered last.
When they decided to change its status to dwarf planet, I looked up the reasons behind it, read up on the complexities of the matter, and could see the reasoning behind the change.
Then again, I hadn't reached thirty yet. Even in my forties I find it takes slightly more time to change my mind on some things...
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).
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.
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.
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.
> 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.
> 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.
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.
Yes, but these figures weren't written in scientific notation so we can't tell. Especially the trailing 0 on 110 is ambiguous because people often write a 0 there where it really is 0 while the convention is that a 0 means it's unknown.
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.
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.
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.
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.
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.
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.
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.
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...
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.
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:
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.
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.
Orbital refueling absolutely changes the rocket equation in a huge way. The standard NASA human Mars plan involves a mega rocket large enough to lift the humans and their supplies in one shot from earth, along with the fuel to get to Mars and the fuel to get back.
Starship enters LEO with empty fuel tanks, meaning it can lift much more payload per pound of fuel. Being refueled in orbit is cheap, because fully reusable flights are cheap. And for Mars, Starship only needs enough fuel to get there, it can make fuel on Mars. That means it doesn’t have to carry even more fuel to fly the return fuel to Mars.
We'll eventually get to the point where Starship-like rockets only ferry people, cargo, and, maybe, propellant to LEO for transfer to spaceships that don't need to go deep into any gravity well. These ships will then take you to orbit around your destination so you can board another shuttle to the surface.
You could probably aerobrake to get into orbit instead. But eventually it might make sense to build ships that are never supposed to touch atmospheres, or only upper layers. Some design constraints can be relaxed then.
There definitely is a place for Aldrin Cyclers, not soon, but eventually. It’s not to save on fuel, but to provide safer and healthier accommodations for the trip.
How it will likely work is passengers will take a Starship to orbit. It will be refueled in LEO, then accelerate to Mars injection velocity to match orbit with a passing Cycler. It will dock with the Cycler, passengers will switch to the Cycler for the duration of the journey. The Cycler will be much roomier, have better shielding, and likely rotate to provide Mars level artificial gravity. Passengers will have far better work, entertainment and workout options.
Once the Cycler approaches Mars, passengers will reboard their Starship, and it will Aerobrake to land, while the Cycler continues on in its orbit, which returns to Earth. The Cycler never slows to orbit either Earth or Mars, it just coasts between them but occasionally will need fuel for course optimizations.
The only problem is that Cyclers will take 9 months to go to or return from Mars. They will be like large cruise ships. Starship can make the trip to Mars in as little as 3 months, and some will still do that. They will be the equivalent of the long distance direct flight, trading a less comfortable and less healthy trip for a big time savings.
In the end you save a lot on fuel - you don't need to bring along shielding, life support equipment for the duration of the trip (only expendables and replacement parts).
The trajectory adjustments may be small enough that Hall thrusters, or even just reorienting solar panels or inactive radiators get enough light pressure to make it work. If we are OK with spending a little more propellant, the cycler can be put on a shorter quasi-cyclic orbit that requires course corrections on every pass (IIRC, the shortest trajectory Aldrin considered in his paper would enter Earth's atmosphere, or crust, I don't remember). The cycler maintenance cycles also don't need to coincide with in-transit crews and, in some passes, crews can bring more cargo (or the cycler can dock with autonomous cargo freighters).
If the cycler is large enough, it may have its own food production, so you don't need to carry that too, but then we can also imagine it as a full habitat that's permanently populated and passes by Earth and Mars every now and then and also plants us firmly into science fiction territory. IIRC, the shortest real cyclic path also takes a trip to the Asteroid belt before passing Mars on its way back to Earth. That, I imagine, would be a popular destination for future space colonists looking for resources in the belt to supply passing cyclers.
That would be a killer trip if it includes the belt. I’d pay for that!
But Cyclers won’t save much fuel. Starships (or their descendants) still have to accelerate and decelerate the same, and still need almost as much shielding (a solar flare during descent once you’ve left the cycler is still deadly).
Most of the starship mass isn’t radiation shielding, it’s reentry shielding, tankage, engines, etc.
But once we get to the Cycler stage I think fuel costs will be low on our lists of concerns anyways.
The most efficient propulsion methods are not suitable for atmospheric flight or landing because of their low thrust, but are excellent for long-duration interplanetary flight where you can "burn" for hours, or days, to change between parking and transfer orbits.
Sort of true. The rocket equation doesn't account for the added weight of lifting the rocket itself, just the added fuel. Multiple launches can reduce the practical overhead, even if not changing the overhead in the limit of 0% rocket mass 100% fuel mass.
Manufacturing fuel in space would be the way to go.
Or eg have giant solar panels in orbit that power a laser to shine at your spaceships. Either to propel them directly, or to transmit power for their ion thrusters etc.
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.
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?
(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).
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?
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.
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.
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.
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.
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.
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.
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...
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. :)
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.
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.
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.
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.
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.
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.
> 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).
> [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.
Similar fun would likely be the safety sheet for FOOF (Dioxygen diflouride), a compound that you can't really get to room temperature without said compound tearing itself and it's container apart. I do recall it reacts "vigourosly" (I believe the paper I read on this used those specific words) with Chlorine triflouride at 90K (-180C, -300F).
To be fair, most stuff involving fluorine is like this. Compare https://fscimage.fishersci.com/msds/11171.htm (for extra chlorine trifluoride fun, this is one of the things you get if you react it with... water. Hence the entry in "unsuitable extinguishing media".):
> Danger! May be fatal if inhaled, absorbed through the skin or swallowed. Both liquid and vapor can cause severe burns to all parts of the body. Specialized medical treatment is required for any exposure... can cause metabolic imbalances with irregular heartbeat, nausea, dizziness, vomiting and seizures. Long-term exposure may cause bone and joint changes. Will attack glass and any silicon-containing material. Corrosive to metal.
> Potential Health Effects
> Eye: Contact with liquid or vapor causes severe burns and possible irreversible eye damage.
> Skin: May be fatal if absorbed through the skin. Causes severe burns with delayed tissue destruction. Substance is rapidly absorbed through the skin. Penetration may continue for several days. Causes severe tissue necrosis and bone destruction.
> Ingestion: Causes severe digestive tract burns with abdominal pain, vomiting, and possible death.
> First Aid Measures
> Eyes: Do NOT allow victim to rub eyes or keep eyes closed. SPEEDY ACTION IS CRITICAL! GET MEDICAL ATTENTION IMMEDIATELY!
> Skin: Discard contaminated clothing in a manner which limits further exposure. Destroy contaminated shoes. Spills should be flushed until medical attention arrives. SPEEDY ACTION IS CRITICAL! GET MEDICAL ATTENTION IMMEDIATELY.
> Ingestion: Get medical aid immediately. SPEED IS ESSENTIAL. A DOCTOR MUST BE NOTIFIED AT ONCE.
> Inhalation: SPEED IS ESSENTIAL, OBTAIN MEDICAL AID IMMEDIATELY. POISON material. If inhaled, get medical aid immediately.
> Wear appropriate protective clothing to prevent skin exposure.
> Wear a NIOSH/MSHA or European Standard EN 149 approved full-facepiece airline respirator in the positive pressure mode with emergency escape provisions.
The statement that it produces no chemicals more toxic than itself is true but misleading because the combustion products will largely consist of chlorine gas, hydroflouric gas (not the acid, the gas) and a variety of other flourine compounds waiting to make your internal metabolism incompatible with life.
I would also argue that CO2 and dry powder isn't an suitable extinguishing media for this, as CF3 doesn't give much of a shit when it's got it's own hyperactive oxidizer on board.
> 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.
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."
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.
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.
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.
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.
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.)
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.
> 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
(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...)
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.
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.
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).
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.
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.
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.
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.
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...
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.
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.
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.
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.
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.
That sounds like water in hydrated minerals rather than liquid water? In terms of settling inner solar system asteroids where the sun bakes everything you're looking for material with as much easily extractable water as concrete to make a comfortable home.
Earth-normal gravity, Earth-normal temperature, Earth-normal pressure, concentrated solar power, breathing air is buoyant, plastic and carbon fiber structural material--and breathing air and water--are convertable from atmosphere, cloud water is heavily enriched with deuterium. Way nicer than Mars.
You can operate an unshielded nuke plant tethered some distance below your balloon habitat, no worries about leaks.
We don't know whether humans can survive for long at Lunar or Martian gravity. Zero-G we know is a problem. So, Venus might be the only other notionally habitable planet.
Saturn, Neptune, and Uranus also have very close to Earth-normal gravity. I don't know what a human habitation at surface-level would be like on such a world, or how to escape the gravity well if you ever wanted to leave, but when it comes to surface gravity, it's pretty weird that our planetary system has five planets with almost the same gravity.
It's either an amazing coincidence, or something about planet formation in our solar system that makes ~1G planets very likely.
Gas-planets would be a challenge with no habitable surface, especially those with high winds. Would a floating sky habitat be any easier than just living in space?
But anything at or near Neptune receives very little light. There's a big gap between Mars and Jupiter (5.2au vs 1.5au), 10au to Saturn, and then a massive gap to Neptune (30au); anything habitable probably needs to be in the Mars-Venus band, fairly close to the sun.
This is possible, but we don't actually know for sure. Only in the last few years has there been hardware on the ISS capable of creating partial-g for rodents [1], and so far (in published research, at least) it hasn't been used for anything except 1g.
> Face it, Luna and Mars are boring, low-value real estate.
It's worth noting that Ceres, and by proxy the vast material wealth of the Asteroid Belt, is only 25% further from Earth than Mars is. The biggest barrier is Ceres has 10% of the gravity of Mars or about 3% of the gravity of Earth. This isn't even close to enough for anything we would consider healthy living.
You think Mars is boring?? I think it's exciting. The more evidence we find that life may have existed there, the less valid our mythical creation stories of earth as the special only recipient of God's hand. Mythology is fun but it's given too much power in certain societies, while science and truth are devalued in turn.
To clarify, according to Bostrom, it would be an indicator of our lower chances of survival (raises priors on Great Filter being in our future rather than past).
The act of finding out if there is life or not will probably raise survival chances on net, compared to never looking.
Much like passively looking for the monster in the dark room. The monster is either there or it is not, but if you see it you have better chances than if you don't (barring some specific contrived scenarios).
If that bothers you, you'll love the nLab's page on the red herring principle :)
> The mathematical red herring principle is the principle that in mathematics, a “red herring” need not, in general, be either red or a herring.
> Frequently, in fact, it is conversely true that all herrings are red herrings. This often leads to mathematicians speaking of “non-red herrings,” and sometimes even to a redefinition of “herring” to include both the red and non-red versions.
Well, i usually use 'soy meat' example, which is obviously not meat. The case where adjective moves meaning outside of boundaries of original meaning, instead of just making it more precise, is kind of perverse. Perhaps people should use hyphen to make it one term in cases where the meaning is not result of composition (e.g. 'dwarf-planet' and 'soy-meat' vs. 'big planet' and 'pork meat').
Ceres actually has a similar classification history to Pluto, at one time being called a "planet" and then demoted to "asteroid". Later it became a "dwarf planet" when Pluto was reclassified.
Is this actually H2O water? I read the article but I am still unclear.
I am often excited to hear that water was discovered on some planet or moon but its always a disappointment to learn that its liquid methane or some other liquid that is not actually H2O water.
I think you must be thinking of some other word — maybe the fact that "ice" doesn't necessarily refer to water ice. If a science article says "water," they generally mean water unless the author's phrasing is extraordinarily sloppy.
Water usually means liquid H2O. Europa, for instance, isn't liquid water but ice that is squeezed and loosened to the point it acts like a liquid while still being well below freezing and basically just ice sand
The main part is that they found some type of material that is made of table salt and water https://en.wikipedia.org/wiki/Hydrohalite , real table salt and real water.
No, it doesn't create a plot loop. The book explains that all of the H2O on Ceres was used to apply spin to Ceres to create artificial gravity. This is a symbol of Inner Planet's dominance over the Beleter's, because a _real_ Belter would never trade precious water for artificial gravity. This is mentioned fairly subtly in the first book, and is easy to miss while taking in the rest of the world.
In addition the spinning up of Ceres is often mentioned as one the of many engineering feats attributed to Tycho.
EDIT: For scientific context to my statement H2O can be turned into really good propellant. Two of Blue Origin's engines run on Liquid Hydrogen and Liquid Oxygen for example.
I had missed that Ceres' gravity is due to its spin.
Does that mean humans are living upside down in their tunnels compared to Earth?
And if that's the case, surely a spin that's greater than the local gravity should shatter the planet itself as the matter has no reason to stay concentrated around its core right?
No. The fact that Ceres is a sphere implies that its scale is large enough for its material to behave as if it were a fluid and so reach hydrostatic equilibrium. Without serious engineering it would indeed come apart if you spun it up.
I vaguely remember something about Tycho Corporation wrapping cables around it and making it stronger, but maybe I'm confusing that with a Scott Manley video about Ceres in the Expanse.
But yes, walking feet towards the surface of Ceres, head to the core. The core is also where the poor people live in The Expanse, because the gravity is less/worse there together with weird Coriolis effects like this https://www.youtube.com/watch?v=ryrGPjyKhO4
> For scientific context to my statement H2O can be turned into really good propellant
Note that in The Expanse universe, water isn't usually used as propellant, but simply as reaction mass. All we know about the actual propellant is that it's used in fusion reactors and is surprisingly efficient.
> Note that in The Expanse universe, water isn't usually used as propellant, but simply as reaction mass. All we know about the actual propellant is that it's used in fusion reactors and is surprisingly efficient.
It's actually ambiguous if Ceres was spun up before the Epstein drive was invented or not. If the H2O was consumed in an Epstein drive (fueled by D-He3 fusion) then only Hydrogen was consumed to produce thrust. What's not ambiguous is that the H2O on Ceres was consumed
We know that mars was colonized 200 years before the Epstein drive was invented. We know that the OPA was founded about 100 years after the Epstein drive was invented, and that 130 years after the Epstein drive is when the main story starts. We know Earth was the first owner of Ceres. We don't know how old Tycho is, other than Fred Johnson was not the first leader of Tycho.
It's an open question on to what extend the belt had humans in it during the 200 years humans were on Mars before the invention of the Epstein drive. It's safe to say that answer is somewhere between more than none, and less than what is shown during the opening of the series. It's highly plausible Ceres was spun up during that time.
> All we know about the actual propellant is that it's used in fusion reactors and is surprisingly efficient.
Since we're being specific with terminology, if it's used in a fusion reactor, it's not a propellant, since propellant is a combination of chemical fuel and oxidizer.
I suspect that isn't true, but it is an interesting question. There is a lot of water on the planet, some of it spends long periods locked up out of reach of drink ability.
I would guess that at most water has been drunk multiple times, but that there is some miniscule a fraction that moved between icecap, permafrost and deep water table and has avoided being consumed by an animal since it arrived on earth.
I would be interested to read a mathematical estimate of how many 9s of water on earth has been drunk at some point.
There is a related interesting observation that every breath you take contains on average one molecule that was breathed out by Julius Caesar in his dying breath:
My recollection was that Mars raided Ceres for ice, prior to or while spinning it up. It would take a hell of a lot of mass drivers, all pointed in the same axis, to spin up a dwarf planet.
Assuming for a moment the technology/scifi world of The Expanse, one thing that doesn't seem to be a scarce resource is electrical power, due to plentiful nuclear reactors. Wouldn't it be possible to flash brine into steam and separate the h2o from the salt, storing the salt in solid cubes or something?
I think many planets may have life below the surface. The hot core of planets behave like a heat reactor. Somewhere between the hot planet core and cold planet surface there should be a balanced temperature a mix. That mix may have a temperature of 0-37C.
We should be able to do the same on earth first. Where's our underground Polar habitats? I personally see Musks' Boring company" stuff as interesting as the rockets, I wish it where cheaper to build cities/tunnels underground.
> Ceres is the largest object in the asteroid belt between Mars and Jupiter and has its own gravity, enabling the Nasa Dawn spacecraft to capture high-resolution images of its surface
Scratching my head. Trying as I may. But not making sense.
I was confused by this too. I wonder if it means that the spacecraft was able to enter into its orbit and circle around taking pictures, as opposed to one pass by
Yes, clearly every asteroid has its own gravity. I guess what it should say is that it has a strong enough gravitational field to allow a spacecraft to be placed into orbit and have it stay there.
Somewhat related I saw it’s going to take NASA’s new Perseverance rover about 7 months to get to Mars and it’s traveling at something like 25,000 MPH. Since NASA had to take the planetary orbits and launch timing, etc. into account I’m assuming that’s the fastest ideal velocity for the rover but not necessarily the fastest possible.
So I guess my question is, given that Ceres is so much further away than Mars, what’s the constraining factor for faster space travel? Safety? Fuel? Hardware? Technology? If Elon was going to spend every penny he has to get to Ceres as fast as possible, how would his billions best be spent?
Faster is normally not all that important: it's much better to save fuel and send more stuff than to get there a few months earlier. Fuel costs vary roughly with delta-V, the total amount you have to accelerate or decelerate your spaceship. Because of the tyranny of the rocket equation, they aren't linearly proportionate to delta-V, but in general, if it takes more delta-V it's going to be harder and more expensive to send a spaceship there.
Here's a map of the solar system by delta-V [0]. Good news is it's roughly equally difficult to get to Ceres as to get to Mars! It's further away, but it's smaller which means less decelerating when you get there.
For your actual question...you can get faster routes with more fuel. We're pretty close to the limits of how big a rocket we know how to build and still get it to Mars (or Ceres) with a 2-ton payload (enough for a lander, a rover and a little fuel) using the most fuel-efficient route. If you want to get there faster, which might be important for manned missions, you need a smaller payload or a bigger rocket. Or the most likely solution - you launch lots of rockets and join up the payloads into a bigger spaceship in Earth orbit. If Elon's goal was to make a one-way trip to Ceres as fast as possible, he'd be doing mostly the same as he is now - focusing on being able to build lots of rockets and launch them cheaply.
Whoa! Thanks for the awesome answer and the map! This blew my mind:
> Good news is it's roughly equally difficult to get to Ceres as to get to Mars! It's further away, but it's smaller which means less decelerating when you get there.
As someone without any background in science I only ever hear about the journey to moon and mars so it’s super interesting to eyeball the marginal difficulty of getting to different planets on that map. Thanks for sharing!
> It's much better to save fuel and send more stuff than to get there a few months earlier.
Yes. For cargo and probes/rovers. Not for humans. The faster we can arrive, the less supplies are required and the risk of something going wrong while the nearest help is light minutes away is lessened.
> For your actual question...you can get faster routes with more fuel
Not fuel, but more Delta-V. Which may or may not imply on more fuel. Options are: more fuel (rocket equation bites here), less weight, more efficient thrusters, aka higher ISP (see the nuclear propulsion sibling comment).
What this gives you is the ability to use other trajectories besides pure Hohmann Transfers - which are efficient, but slow.
Ideally we would send supplies ahead of time with the most efficient transfers possible, then get humans there as fast as we possibly can. Otherwise this would take a while, around 400 days, one way. So over two years just to get there and back, plus wait time until the next launch window.
Based on the linked (very cool) map, I don’t think what you say is accurate? A flyby of Ceres would be slightly harder than entering Mars orbit, and entering Ceres orbit would be harder than entering Neptune orbit.
Yes for a flyby or orbital mission. I was thinking of a landing mission which costs more delta-V. In practice, you can get that delta-V by aerobraking when going to Mars but not to Ceres, though on the other hand you need to build the spacecraft to withstand the Mars atmosphere. So maybe the answer is "it's complicated" but either way it's reasonably close, not the 5x further you might think from looking at the closest approaches of the orbits of Earth, Mars and Ceres.
The 7 month trip is not the fastest, it's the most fuel efficient because it needs the least amount of dV. Hoffman transfer orbits are what you should google about( and they exist for every planet).
> Dwarf planet, believed to be a barren space rock, has an ‘extensive reservoir’ of brine beneath its surface, images show
Believed by who? We already knew it was made substantially of ice. Isn't this just discovering that some of it is liquid?
Wikipedia quotes a PDF from 2017 regarding the quantity of ice, and by then the fact of Ceres having so much ice had already been worked into the story line of The Expanse.
