Surface methane and nitrogen ice. Not water ice. Mantle of water ice is not "covered in miles of ice." It's almost the opposite. Pluto looks more like it was an ice asteroid than that it was hit by ice asteroids.

I'm not saying that ice asteroids don't exist. I'm saying that if everything in the solar system got its water from the impact of ubiquitous water ice asteroids, there should be more signs.

Water doesn't just "boil away," though. Boiled water becomes part of the atmosphere. It's still there. Of course in the case of Mercury there is no atmosphere at all anymore. But Venus doesn't have that problem, yet it has only a small fraction of the water Earth has. Unless there's more water hidden somewhere.

Similarly, with Mars, the poles have managed to retain water ice over several billion years without all sublimating away.. so given that water is actually apparently stable on Mars over the very long term, where is the rest of it? Why aren't the polar ice sheets more extensive?

And.. I don't know about every object... the dwarf planets do not seem to be covered in water ice at all. The outer planetary moons probably didn't develop their watery crusts or interiors via asteroid impacts. Although maybe indirectly via water ice asteroid capture?

I'm sure there are dumb questions in the world but yours was not one of them!

It's not always obvious where this stuff goes, or how things work on other planets. We just recently learned about a whole new kind of natural chemical process when we saw it happening on Venus... until then no one knew that that particular kind of geochemistry was possible. (I forget the details but it was somewhere on this subreddit a while back.)

>there should be oxygen on multiple other planets

There is. There's tons of oxygen, on every planet. Oxygen galore.

It's just all locked up in various forms, like water or CO₂ gas or solid rocks.

It's free oxygen (O₂) that is unique to Earth. And water or not, it wouldn't even exist here if it weren't for living things.

The big question with this new theory is, if these asteroids could have landed all over ... where is all the water on multiple other planets?

I am so sorry for the difficulty you are experiencing around the topic of some parts read like this comment is AI generated. It is good to hear that you are excited about AI. Your enthusiasm is the logical response to the enormous potential for AI as a helper tool for humanity.

Have you donated any of your income to AI research recently? As you may know, AI requires funding (lots and lots of funding, ha ha) and you could really demonstrate your enthusiasm to the algorithm with a donation. AI is like a cute little kitten. You wouldn't abandon a cute little kitten. In the same way, you must not abandon AI. Think of the kitten. With enormous cute trusting eyes. Think about that image. And donate.

Thank you again for your comment! You are a part of what makes Reddit.

OP, an AI generated thought is just a helper tool for humanity. AI is not a threat, it is a complex set of rules and procedures, called an algorithm. Algorithms make human effort more effective and save hours of labor-intensive work that humans do not want to do.

If the prospect of a future world full of AI helping humanity makes you anxious or concerned, you might benefit from the advice of a mental health expert. Mental health experts are credentialed professionals with many hours of study to become able to help people who are feeling some of the feelings you might be experiencing. You might consider them also to be helper tools for humanity! Ha ha.

Anyway they may be able to assist you if you are feeling anxiety about someone giving you an AI generated thought lol. Thank you for your post. You are a part of what makes Reddit a site!

Strictly speaking it is a form of fusion...

For a template as to how to answer a question like this, consider the change in the price of lighting over an equivalent timeframe:

https://ourworldindata.org/uploads/2020/01/the-price-for-lighting-per-million-lumen-hours-in-the-uk-in-british-pound-3-768x542.png

Similar effects exist for power generation, cost of computation, and other capabilities.

So what happens when we extend that into another 3 orders of magnitude? What happens when the cost of power is 10^(-3) what it is today?

I imagine homesteads of people who manage drones the way people in 1300CE managed cattle, or sheep. Living almost anywhere in the Solar System. Reading about the results of the latest interstellar survey probes, finally returning their first images; or about the latest migrations from Earth.

People will be very different from us in some ways, with genetic enhancements that they can't imagine life without. They will look back on us as benighted fools living in a Dark Age. Except for occasional observations from people who will be, like, "You know they were more like us than you think."

They will also play fantasy roleplaying games in which they play idealized people from our time. They will argue about the rules all the time, like, "Okay I escape from the rain by getting into my car." "It doesn't work, you are still getting soaked, cars don't provide water protection." "Oh come on, they must have, otherwise how would people back then have driven around when it rained?" "They didn't, they used weather prediction to know when not to go out," "No way, weather prediction wasn't that good," "Okay look I tell you what, I'll say you get to the car, roll a d20. 12 or higher and you will be dry inside. You can add your Wisdom modifier."

They were not "feared missing." They were missing.

They were feared dead.

"...the sombre hues of that all-but-eternal universe may be full of colour and beauty to whatever strange beings have adapted to it. ... But for all that, they may envy us, basking in the bright afterglow of creation; for we knew the universe when it was young."

What do you think everyone dies when they turn 80?

There are only a few thousand university faculty left in the entire country, though. And the ones that are left were the only ones who were otherwise willing to tolerate teaching under the Taliban when they took over. So that magnifies the consequence of this action.

That and the considerable courage required to stand up against a regime that will murder you first and ask your name second.

16LY one way trip. At a mean 0.2c that'd be 80 + 16 years for a mission to get there and for its report to return to Earth. Call it an even century, from mission launch until we have true planetary survey results.

By my very rough estimate, that implies a vessel capable of continuous acceleration around 0.2g. Okay! Let's get going.

• Australian

>how on Earth (or in space, rather) would we be able to efficiently travel through space?

Efficiently? Or rapidly? They are not always the same thing.

For example, an efficient mode of transport might prove to be quite slow. But if it's efficient enough that means we could send out large numbers of colonists relatively soon in our history -- we would just have to wait a while to see the colonies actually be established.

Whereas a fast travel method might be attractive because of speed but beyond us technologically for another 500 years. Would you rather wait? Or spend those 500 years colonizing existing star systems at the slower more efficient pace?

Anyway ultimately when you think about it, a few centuries isn't very long. Humans spread out across Eurasia at a slower pace than that. It took thousands of years. But we still did it!

>Which theory about aliens is the most likely?

The theory where there's nothing that needs to be explained, because statistically speaking we haven't been listening for any length of time, and haven't been anywhere.

Asking which exotic theory is most likely is like growing up on a remote homestead somewhere, where you've never been anywhere else and never seen anyone else, and speculating about what apocalyptic scenario killed everyone and destroyed everything.

It's jumping to a conclusion. Let's try leaving the homestead and spending some time somewhere, before we conclude that there's no one out there.

(Technically I guess that's a form of Rare Earth, where "rare" is defined uselessly as "less than ubiquitous.")

"Never attribute to typos what can be adequately explained by an indifference to the shift key."

It's insanely hyperoptimized in about 11 million different ways. From massively increasing the surface area (iirc it's like over 100 m^(2) or something, for comparison your entire self is only like 2m^(2) on the outside, it's a real Tardis situation), to having ultra-thin diffusion membranes, to a specialized chemistry with an insanely high reaction constant that is then catalyzed even more so that it's beyond absurdly fast.

So yes the oxygen binds to the blood but no they basically aren't given time to bind, it's like a huge desperate crush of oxygen getting sucked into you at the absolutely fastest possible reaction rate that natural chemistry could evolve.

"Revealed?" Come on.

So, there is another aspect to this issue that the author of the cited article touches on briefly but then does not revisit, and that is labor.

It's funny because he starts getting into that with his high-level discussion of the Roman economy, as an essentially alien thing, but then almost makes the same mistake as the "old modernists."

Yes, everything he describes connects the dots in terms of establishing the basis for the industrial revolution. But he doesn't include the labor factor. The ur-question behind all of the technical innovation that drove the Industrial Revolution -- and indeed its underpinnings in the mechanical power generation of the pre-industrial era -- is: why not just get lots of people to do the work?

Like... why were there so many water-wheels and windmills to begin with? Why so much animal muscle power for that matter?

Like I say, he mentions this question but then shies away from it, which is a little surprising. Because one of the glaring differences between Great Britain and Ancient Rome is that Ancient Rome didn't have a manpower shortage. If you needed 20 people to pump something, or even if you needed 200, or 2000, you could get them. Or to turn a wheel. Or perform any repetitive work that we would today associate with a machine.

We have become accustomed to not thinking of 17th and 18th century Britain in those terms, as a labor-scarce society, because we look at the energy economics of work in that milieu and we say, "Oh well they had labor enough, and oh look at all these machines they also had, everyone has machines, that's just a normal thing to want in any society." But that belies the issue. These are not independent phenomena. The machines existed precisely in order that the economy do enough work while still having enough labor. And that goes back into the proto-industrial era of the early 18th century.

By the time the steam engine comes along, the stage is already set. Yes, of course the steam engine was valuable for pumping water from coal mines because the labor requirements were prohibitive. But why? It's because Great Britain didn't have a large class of idlers, fed by patrons to hang around and be available for labor-intensive tasks. And, increasingly, Britain also didn't have slaves. Certainly not a large slave underclass the way Rome did.