According to Wikipedia this planet has an estimated surface gravity of 12.43 m/s2 with a margin of error of about 2 m/s2. That’s only up to 50% higher than Earth’s 9.8 m/s^2 (on the high end of the error margin) so it probably would be possible to get into orbit.
That said we don’t actually know much about it for sure. We don’t know if it’s a terrestrial planet for example. It could be composed mostly of gases and liquids like Neptune.
(Not a rocket scientist or mathematician, but I spent 100s of hours playing KSP RP-1)
Just doing some estimates using data from the wikipedia page:
The dV (delta-V) needed to get into low Earth orbit is around 9.4km/s.
The dV for K2-18b might be around 19km/s, more than double that of Earth’s.It’s practically impossible I think, you would need such a massive launch vehicle. For double the dV, you would need exponentially more fuel assuming current rocketry tech (fuel+oxidizer tanks and engines). There wouldn’t be any single-stage or two-stage rockets that could do this. With a 3 or 4 stage rocket maybe? But you would be sending nearly 100% fuel off the launchpad with virtually zero payload.
Check out the “tyranny of the rocket equation”. The more propellant you need to lift heavier rockets, the more propellant you need to lift that extra propellant and so on and so on.
I tried to factor in:
spoiler
- Atmospheric drag - K2-18b’s atmosphere is quite dense with a huge radius:
The density of K2-18b is about 2.67+0.52/−0.47 g/cm3—intermediate between that of Earth and Neptune—implying that the planet has a hydrogen-rich envelope. […] Atmosphere makes up at most 6.2% of the planet’s mass
-
Since the atmosphere is so thick and takes up a lot of mass, I’ve picked 500km as the low orbit altitude (comparing to Earth’s ~100km Karman line, it makes you appreciate how thin our atmosphere is ).
-
Rotational assist - I’m assuming it’s tidally locked since it orbits so closely to its star (33 day years), and so you wouldn’t get the assist from rotation like you do on Earth:
The planet is most likely tidally locked to the star, although considering its orbital eccentricity, a spin-orbit resonance like Mercury is also possible.
Kerbal Space Program is such an amazing game that secretly teaches you physics.
game that secretly teaches you physics.
those are the best!
I’m stealing this
Nice. It’s from XKCD if you want the source.
What about something like nuclear pulse propulsion, or some kind of massive spin launch?
Nuclear propulsion, like Project Orion, would probably make it more likely they’d manage to get out of orbit. No idea on the math here, tho
https://en.wikipedia.org/wiki/Project_Orion_(nuclear_propulsion)
If it’s tidally locked, no spin assist.
Missed that part but that doesn’t preclude what I was saying, just requires “more” of it
Likely tidally locked
With a denser atmosphere, wouldn’t that mean that you could get more lift from a traditional aerofoil than on earth? And if so, wouldn’t that technically make it easier to start from a high enough altitude that at least some of the gravity is mitigated?
Let’s say you do the same on Earth. If you fly to the top of the atmosphere you are 100 km above the ground. That’s a 1/60 of the distance to the center of the Earth. You don’t have to fight air resistance but gravity is almost the same, if I’m not wrong, less than 1% of difference.
You don’t have to launch from the ground, there are many things that can be done to allow them to reach orbit. It’ll be an enormously bigger undertaking but the physics doesn’t make it impossible. No reason to think of it in terms of our current situation either, what we are behind our current science when it comes to rocket science, due to * waves at everything else *
Pretty late response, but if the atmosphere is that dense and hydrogen rich, you could reduce the start amount of fuel by a lot and capture it directly during flight? Needs some elaborated technology and low angle flight vector but could work, does it?
It’s probably still a lot harder though. You’re not just heavier, but also slower which means you’ll spend more time fighting gravity. And all the extra fuel you bring for that makes the rocket heavier which means you need even more fuel to launch the fuel. Higher surface gravity likely means a thicker atmosphere too which is a big issue and a more massive body also has a faster orbital velocity. Although in this case the larger diameter might counteract that a bit because higher orbits have slower velocities.
My point is that this would probably still be a lot harder than just building a 50% bigger rocket. If you’ve ever tried launching from Eve in Kerbal Space Program you know the pain. Although in that case you also have to fly the entire rocket there first which is its own challenge.
you’ll spend more time fighting gravity
Aw man. This is already a significant portion of my day.
I assume it’s not just about the gravity, but also the much larger radius of the planet would mean much larger distance from the surface, and thus much more fuel needed.
You’re sort of right. The change in distance from the surface is insignificant, but a spacecraft orbiting a bigger planet has to travel further with each orbit so its speed must be faster to avoid falling out of orbit, even if the gravitational acceleration at its orbital height is the same.
That’s not how…what???
F = G * (m1 * m2) / r^2
Note that radius is both squared and the dividing term. More distance = less gravity
Escape velocity does scale with (square root of) radius so its not a dumb thought.
And I’m not a rocket surgeon but I could imagine earth rockets might be operating near some physical limits that make a 50% increase (or whatever) infeasible.
Wikipedia says
energy = GMm/r.if
g=GM/r²thenenergy = mgr, proportional to r given g is constant.apologies
My previous comment was wrong, I derivated while integrating.
I stated an assumption and was contributing to the conversation. Even if that assumption is incorrect, there’s no need to be a dick about it.
It seems like a larger atmosphere would result in a longer duration exposed to atmospheric drag, thus requiring more fuel to overcome it.
I’ve been wondering what a hypothetical perfect habitable planet for spacefaring would look like. Could you have one where a plane line the SR-71 Blackbird or an even less capable aircraft could simply “fly” into orbit? Or what about something Earth-like but with a flat plateau at 15,000 m where you could launch rockets from?
Mars is better for launching rockets into deep space than Earth because it has a lower gravity field and also thinner atmosphere.
Classic planes require an atmosphere to generate lift. There’s an outer limit where that would be a viable mechanism, and on Earth it’s still far below LEO. Still too deep in the gravity well for ion thrusters to be viable. It requires chemical rocket fuels to bridge that gap.
Maybe someday fusion propulsion will break that limitations, but for now the best you can do is reduce the amount of fuel needed by flying to the upper atmosphere and reaching hypersonic speeds before kicking into rocket fuel propulsion.
Then after orbital injection, switching to ion thrusters to move around, and solar sails for exiting orbit into interplanetary/lunar routes.
Imagine a terrestrial planet that is Earthlike in all respects, but it simply has more persistent cloud cover, such that seeing an open cloudless sky is miraculously unlikely, as unlikely as humans directly witnessing an asteroid impact.
No ground based astronomy.
No technological discoveries or culture that derives from ground based astronomy.
No celestial navigation on the ground.
Very different / stunted / more difficult cartography.
Technological civilization is capable of emerging, but it would not be able to well understand anything beyond the terra firma, not untill it generated aircraft capable of breaching the cloud cover layer, and thrmen developed airborne observatories.
“Nightfall”, by Arthur C. Clarke is a short story based on this premise.
Except in the story it’s a complex multiple-star solar system that makes it very rare for all suns to set at once.
Edit: It’s actually Isaac Asimov.
Augh!
You’re telling me there’s an Arthur C Clarke short that I missed?
Damnit I am losing so many nerd points today.
I have written a post about exactly this phenomenon, arguing that that’s how most animals/insects see the world (assuming their sense of vision isn’t good enough or they just don’t care to look up). Apparently i was wrong, even insects can see the stars and navigate due to their light (milky way navigation).
Well, the church threw us back about a millenia, so what’s a few centuries.
Is there a particular instance you’re referring to here? Because contrary to popular belief, the church has historically been big on investing in what we now call science.
For instance, although the trial of Galileo is often characterised as “big bad church holds us back because religion is opposed to heliocentrism”, there was actually a lot of legitimate scientific beef against Galileo. Although he ended up being right about heliocentrism, he didn’t really have good evidence to support his claims; He didn’t understand Kepler’s laws of planetary motion, and his telescope produced so many aberrant artifacts that astronomers who use it were reasonable to be dubious of his claims.
If you’d like to learn more, here’s an excellent video by Dr Fatima, an astrophysicist turned science communicator. The philosopher of science, Paul Feyerabend also uses Galileo as a case study in his book Against Method
Because religion contradicts scientific approach to thinking. I personally like the way in which Carl Sagan gets rid of all the “noise” information when investigating how the world works. Religion is a noise
Because religion contradicts scientific approach to thinking
Any scientific base for that claim? Because there seems to be way to much religious scientist for it to be true.
Well, as soon as they invent radio and experience interferens radio astronomi will evolve… I guess?
I wrote and tried publishing a short story about a species like that.
where only occasionally people on top of mountains see stars, and they chuck it as a consequence of low pressure. eventually they invented flight, and assume pilots going high enough to see stars are having cognitive issues due to lack of air.
They asked pilots to draw the stars they see, and they get different drawings (they sent pilots at different times of the year because they couldn’t ever expect stars to shift) and assume its proof that thise stars are a cognitive artifact.
Eventually a pilot swears they are real and can actually use then to navigate, skepticism, he proves it. brand new research field emerges.
Although the story focuses more on deep DEEP time an omniengineering. (A term I just made up because mega engineering is a concept way too small compared to the one in the story).
If you want I don’t mind putting that story in the conversation.
Heck yeah, I’d read that. Feels like it could have been a Hal Clement story idea.
https://docs.google.com/document/d/1PTzQQKXLnBL1ICUK8IYa8YoUSD2ncQk5-jse-FaFPAI/edit?usp=drivesdk
tried putting the text in a comment, but it’s too long, I enabled comments.
Thanks! Will review.
no pressure. and be honest, if some parts are shite tell me. and especially if it is all shite.
Post it for sure
https://docs.google.com/document/d/1PTzQQKXLnBL1ICUK8IYa8YoUSD2ncQk5-jse-FaFPAI/edit?usp=drivesdk
tried putting the text in a comment, but it’s too long, I enabled comments.
I loved it. Thanks for sharing!
I’d read it
Shit yeah go for it, I love those kinds of stories!
Have you read Hitchhiker’s Guide to the Galaxy?
Hah, actually no I have not.
-1 nerd point lol
Good news: it’s all public domain (edit: it isn’t). Whole series is there, at least the public domain ones. There was a newer one that wasn’t public domain when I last checked, though that was a long time ago and it might be now.
Don’t read it for nerd points. Read it to find out why it’s associated with nerd points.
Edit: disregard above, no idea where I got that idea from, maybe from how easy it is to find the full novel online just by doing a search for it, I must have figured and then somehow along the way it turned into a fact in my mind.
Series? More then one? So long and thanks for all the books!
Don’t want to spoil anything because you really should, but this is very reminiscent of a plot point in one of the books.
If the planet is massive enough, getting to orbit becomes a real challenge because fuel consumption scales roughly exponentially with the mass of a planet (delta-v formula, rocket equation).
This leads to an almost sharp cut-off for the maximum mass that a planet can have so that a rocket which utilizes chemical fuel (e.g. methane+oxygen) can still reach orbit successfully. This maximum mass is roughly 10^26 kg.
For reference: Earth’s mass is around 6*10^24 kg.
While other propulsion types exist, such as nuclear + ion drive, these propulsion types are significantly more complicated.
Interestingly, if a planet is too small, it cannot hold an atmosphere. There is a surprisingly sharp cut-off minimum mass for this as well, at roughly 10^21 kg.
We really are in the Goldilocks Zone, aren’t we?
Well, yes. In the middle of the goldilocks zone that is based on the environment we are adapted to is where you would expect to find us :p
Haha fair point.
Only if there are not sentient life forms on that planet capable of getting off it
What if, and hear me out… Giant trebuchet?
I suspect that atmosphere composition makes different options more or less viable.
The difficulty/cost getting to orbit probably also would influence where a space elevator lands in terms of developmental priority.
I did not know that. It’s because it interferes with gravity? I’m dumb sorry
Not enough gravity, the atmosphere will drift away from the planet with the help of solar winds etc. Too much gravity, and the ammount of fuel you need to leave the plannet weighs more than the rocket the fuel is being used to lift can carry.
Even in our current ships, most of the fuel used to leave orbit is really used to carry the other fuel you need later.
That’s interesting! Thank you!!
Jokes on us: Because of the gravity issue, alien life on such planets jumps right to stargate technology.
“They spent almost a thousand years fooling around with rockets!”
Uhh, one stargate doesn’t go anywhere.
You can accelerate it into space at g forces which would liquify living beings, perhaps?
I’d say they stand a whelks chance in a supernova of that succeeding.
that’s why you communicate via radio waves to other life in the area and build a network
The interesting thing about this is that it could be a double whammy. The collision that formed the Moon not only made Earth smaller, it also ejected a lot of material away from the orbit. This made Earth even smaller than it would otherwise have been, had the two bodies merged. And the Moon also formed in the process. The Moon causes the tides which are theorized to have a significant beneficial effect on evolving more complex forms of life.
So just being small might not be enough and having a big moon might also not be enough, but Earth was lucky enough to have both. And that’s just some of the things in a long list of things that have to go right to get complex life on a planet.
My feeling is that life is pretty rare, but given there are so many star systems in our galaxy there might be a lot of it still. But most of it is probably very simple stuff. Getting to where Earth is, might be a once every couple of millions of years event within our entire galaxy. So there really might be nothing intelligent out there at this moment in time, there might have been earlier and there might be in the future, but for right now we are it.
Fun fact worth noting: humans and octopodes split back when our shared bodyplan was effectively a worm who just got legs. Octopuses have been shown to be able to learn and memorize letters, patterns, their different keepers (e.g., spitting at one particular keeper they didn’t like), etc., and all the intelligence they’ve been demonstrated to learn evolved separately from humans.
So we’ve actually got two examples of “worm with newly-evolved legs” becoming pretty damn smart on Earth, not just one - which makes my bet more on the “if the biosphere got to worms with legs, there’s a lot of smart stuff there”
I hear a biologist once say that if the octopus could live to be 80 like humans, they would be in charge of the planet instead of humans.
The main disadvantage octopi have is their antisocial behavior. The parents don’t raise and teach their young. They live in solitude. The only time they spent time together is for mating, after which they die.
Octopuses that can talk to each other, hunt in groups, and raise their young collectively would be pretty formidable. Even if they managed to get there, they would still be living underwater making the use of fire pretty difficult.
Children of Ruin is a great book that describes a civilization of octopus, if you want to explore this a bit.
And that’s just some of the things in a long list of things that have to go right to get complex life on a planet.
There’s ground bacteria that adapted to live in human-made tar lakes, digesting tar instead of straw.
I assume the amount of energy required for ‘only’ 50% more is massive.
Apparently with 50% higher gravity it would be pretty much impossible with chemical rockets, but with the median of the estimate (so about 12.43 m/s2) it would be possible, you’d just need an incredibly large rocket, or non-chemical propulsion (e.g. nuclear).
A space program on that planet would definitely advance much slower than on Earth.
How well funded have our space programs been? Maybe they aren’t diverting massive portions of their resources to war and can actually focus on space.
They were well funded back when their real goal was to develop ICBMs capable of delivering nukes.
Much slower as in hundreds or thousands of years, so practically no difference at all.
Also i wonder since the diameter is larger, is this effectively like putting everything in a higher orbit which is also more difficult then if it was just twice as dense.
I’ve been wondering this for years now. Sci fi and even actual scientific speculation tends to assume aliens would be way ahead of us in terms of technology because their planets may have been formed earlier. I don’t think time alone matters. If they don’t have resources, if fhey don’t evolve the same way, if they have more difficulties in doing shit due to any number of reasons… They could be far less advanced than us. Maybe nobody in the entire universe has figured out how to realistically travel between stars yet. Maybe we are the only ones who have even managed to get off our rock.
Imagine humanity in 1000 years. We would be among the stars.
Now imagine humanity in 10000 years, 100000 years or even 1000000 years.
A million years is still a fraction in the cosmic timescale.
It would be nearly impossible to have other civilizations be on exactly the same technological level as us. They would indeed be either much less advanced, or much more advanced.
With all the crazy ass things that can kill us off, I don’t think we’re alone in the universe, but we may very well be alone in time.
The Fermi Paradox might just the the likelyhood to get wiped out from motions to everything and we’re too far away to get contact in this gnat’s ass of a conscious timeline we’re in.
Maybe they just don’t want to leave their planet because it’s dope af
Some humans want to travel even when they’re perfectly happy.
There still is the „Early Bird Theory“.
When you look at us, the Earth, life has formed almost immediately after the conditions where given. On top of that the universe itself isn’t even that old. There is a good chance, that Fermi was right but we are just the first ones.
… which makes me think that whatever or whoever designed us had some work left to do. You left in some bugs buddy.
There’s also a theory that we’re too late, and that our existence is like the remaining microbes in a puddle of water in a desert.
The universe used to be lukewarm with conditions for life to exist everywhere, until it expanded and started cooling.
On a positive note, this could also mean that life lies dormant everywhere just waiting for the right conditions, so that anywhere that has the right conditions also has life.
I wonder what another being would need of us if it was already able to travel through the vacuum of space while self-sustaining.
They’d want our coconuts, I bet. They’re pretty cool, I bet aliens don’t have coconuts. They might have some cool alien fruit to trade for coconuts. Or weed.
alien pointing at a coconut tree
Look, m’lord! Horses!
This is just arrogance.
We have only been announcing our intelligence for 100 years. It takes 100,000 years just to cross our galaxy. No-one knows we are here yet.
There’s also the Dark Forest hypothesis - the idea that maybe many alien civilizations exist out there but stay silent because revealing themselves would make them targets/prey to a more high-tech hostile civilization.
I’d imagine any intelligent alien life form would be intelligent enough to realize that they’ve reached a point at which they can simply life in a sustained utopia. Heal the planet, work less, fill time with hobbies and pursuits. Humans have this flaw, and it’s that the mentally ill squander the world’s wealth and use it for dick-measuring contests. A small minority of us will kill their own mother for a job promotion, and the people at the very top want to squander it all so they see another 0 in their bank account, or outrace the other 7 megabillionaires to the dick-measuring contest on Mars. I could only hope aliens aren’t as as stupid. We could just litter the earth with trees, solar panels, 2 br condos, and hammocks, and have AI work for us, but nope. Every single die shrink leads to more transistor density and never any power efficiency because big numbers are better for shareholders. They sold us downstream. If any alien contacts us or leaves a trace they’re most likely just as dangerous to our survival as we are. Space conquistadors
3 body problem is a good book for thought experiments, but it didn’t really discuss the arguments against the dark forest hypothesis
-
assumes universal hostility.
-
Interstellar warfare is protracted and impractical.
-
Ignores potential cooperation and ethical diversity.
-
assumes aliens think like humans
Regarding the first point, I think it just assumes the possibility for hostility, not the universality of it. If there’s a room with a thousand people and I know one person in the room has a gun and wants to kill me, I’m still going to hesitate to enter regardless of the 999.
Also, any intelligence that arises out of evolution is going to have at least the rough concept of violence.
Counterarguments
The 999 are going too overpower the violent 1.
The concept of peace will be known and experience will have demonstrated that it is more valuable than war.
Counter-counterarguments.
That assumes the 999 are in a position to stop the 1. Assuming FTL travel/communication/detection is never possible, reaction ability is always going to be limited. A relativistic projectile aimed at a planet can be a silent civilization killer.
This is more about cautiously reacting to the possibility of hostility in the very high stakes scenario of first contact, not the confirmation of hostility. In the room analogy, we don’t know who has the gun, whether it’s truly 1 person or 0 or 100 or 500, if most or all of the 999 are blindfolded or willing to defend newcomers, whether overpowering the violent one(s) is actually possible due to everyone being spread out and any guns having functionally unlimited ammo, whether other people have already been taken out for just showing up or resisting, and whether all of the above even matters if the aggressor gets a kill shot off before any of the above takes effect.
Evolution is inherently a competition for limited resources with winners and losers, so violence innately comes with the territory. Even grass and trees are in a war for sunlight. The concept of peaceful cooperation may be common due to the individual specialization likely needed for a species to become space-fairing, but it’ll be a higher level, more abstract idea, and the universality of other species applying it more broadly cannot be assumed.
Yes. Those are the book’s arguments. A counter-counter argument is a repeat of the same argument.
-
It’s not convincing because it’s impossible to hide. You always produce waste heat which would be visible (if you use 100W of solar power, you dissipate 100W in deep infra red into space)
We would expect to see stars putting out an amount of energy for a bright star, but in deep IR as they’re wrapped in Dyson spheres or swarms
I don’t think you could exhaust the waste heat of a civilisation in a black hole. Perhaps a civilisation living in computers could, but not a biological one
We make a mistake by assuming that life forms would likely be at the same scale as us. Larger planets would likely develop life forms appropriate for those planets instead of appropriate for ours.
Most of the life we see on Earth isn’t even our size!
Life on earth scales from microscopic bacteria all the way up funguses that have an underground network covering thousands of acres.
The chances of us finding life on another planet is pretty slim, the chance of that life looking like us is astronomically miniscule.
Uh… being smaller or larger does not really change the laws of physics… if the gravity is too high, no fuel has enough energy density to escape the gravity of the celestial body.
If you need 150kg of fuel to get 100kg worth of matter to escape velocity it does not matter how much fuel you have. It will not ever be enough to leave.
The tallest people on that planet
A while back I read an article that stated earth was about as high G as you could get and still be able to get to orbit with chemical rockets (barring huge leaps in tech). I could be remembering that badly though, so take it with a grain of salt
To everyone saying launching to orbit is impossible, I have two words: Orion Drive
so it’s possible, once
Getting to orbit? I don’t know if they can even stand up 😆
What does not kill them makes them stronger? 😎
John Carter of Mars? That you?
It might take them a few more centuries than us to develop the tech, but just because we use chemical engines doesn’t mean it’s the only viable method. I’m sure they’d figure something out eventually.
I’ve played kerbal space program with increased gravity, you just have to use asparagus staging, no prob!
They’ve just got to dig a hole down through the core of the planet and then drop craft down the hole to “slingshot” them into orbit.
