What If: The Moon Is Habitable

[Lord MJ]

Imagine that the Moon is habitable and it has been habitable for as long as the Earth has been habitable.

Now lets assume two scenarios.

1. The moon has no intelligent life on it but it does have vegetation and animal life (or whatever is the equivalent of animals in an alien ecosystem).

2. The moon has intelligent life on it with a rate of technological advancement that parallels our own to the point that our development is only a few years distant from their development.

In both cases how would the existence of a habitable moon effect the development of human civilizations. When would human science realize that the Earth is habitable. When would humans be able to determine that intelligent life exists on the moon? How would it effect Earth's religions. I'd imagine that our religions would've evolved quite differently if the moon was habitable. I'd imagine that some people would believe that the moon was literally heaven.

There was several variations on this theme that can be explored. What if instead of our technology levels being equal the moon-men's technology was 100 or 200 years ahead of Earth's? The last couple hundred hears of our history would be drastically altered.

[Pablo Sanchez]

The moon would have to be much larger to be able to support life, so I'd have to ask any resident physicist/geologist whether a double-planet system of two earth-sized objects could result in both being capable of supporting life, or if the tidal forces at work would in some way prevent this.

[Ziggy Stardust]

When would humans be able to determine that intelligent life exists on the moon?

Pretty early, I'd imagine. IIRC, in real life the first detailed sketch of the lunar surface was in 1609. If there was intelligent life on the Moon, it would be very readily visible once people start looking through telescopes long enough.

[The Duchess of Zeon]

A more interesting question is what would have happened if Venus had avoided a spiralling warming cycle and was habitable in the present, with a functional ecosystem of its own verging from jungles around the small detached seas to large inland desert areas and some Serenghetti-like climatological zones at the poles. It doesn't, unlike this, require any changes to the astrophysical makeup of the solar system.

[Junghalli]

The space program would certainly get a major boost. In the uninhabited moon scenario I could definitely see us already having colonies there.

In the inhabited moon scenario, with the two civilizations developing civilization at the same time, I imagine first contact would have taken place in the early twentieth century, with the development of radio. The two civilizations would probably have been exchanging messages for decades by the time a moon mission became feasible (or an Earth mission - no reason to necessarily assume the humans would be the first ones to try sending people).

The moon would have to be much larger to be able to support life, so I'd have to ask any resident physicist/geologist whether a double-planet system of two earth-sized objects could result in both being capable of supporting life, or if the tidal forces at work would in some way prevent this.

The biggest problem will be that a bigger moon will make bigger tides. Let's say this moon is 1/3 the mass of Earth (this is probably around the minimum you need to have Earthlike conditions after 4.5 billion years). It'd have around 30 times the mass of our moon, and the tides would correspondingly be 30 times stronger. I suspect the result may be an Earth and Mars tidally locked toward each other. If not, you'll have some truly massive ocean tides, which would probably make much of the coastal plains uninhabitable. Either way, conditions on Earth would be changed considerably. The megamoon would probably have geologic effects as well. In a tidal locking scenario you might end up with a permanent Pangaea-like landmass on the far side and a massive midocean sea floor spreading zone right under the point where the moon is directly overhead. This means that assuming humans exist in the scenario (realistically they shouldn't) they probably wouldn't even know the moon existed until some adventurous explorer sailed into the near side hemisphere. It'd be interesting to see what they'd make of it.

You might be able to compensate for this by having the moon be farther away. I'm not sure how far away you can make it before it's no longer gravitationally bound to the Earth though.

How would it effect Earth's religions. I'd imagine that our religions would've evolved quite differently if the moon was habitable. I'd imagine that some people would believe that the moon was literally heaven

I don't know about that. It's not like ancient people would have know whether or not the moon was habitable just by looking at it. Galileo thought he was looking at a habitable world when he was seeing our moon. It probably wouldn't be until the beginning of the scientific era that people would realize the moon was habitable.

[erik_t]

The moon would have to be much larger to be able to support life, so I'd have to ask any resident physicist/geologist whether a double-planet system of two earth-sized objects could result in both being capable of supporting life, or if the tidal forces at work would in some way prevent this.

I don't think this follows. Titan is only about double the mass of Luna, yet it has an atmosphere of about 1.5x Earth density at the surface. And certainly STP isn't necessary for intelligent life; La Rinconada, Peru has only about 63% sea level density, yet has some 30,000 inhabitants.

There's a definite question of how a life-supporting atmosphere could form on Luna, but a substantial atmosphere on a body of that size certainly seems possible.

[Lord of the Abyss]

The super-sized Moon could just orbit farther away, which would reduce the tides I think ?

The Moon as I understand it is already big enough that it could hold on to an atmosphere for some time ( 100,000 years ? A million ? Something like that ). It can hold down an atmosphere, mostly; it's just that the gas molecules near the edge drift away, slowly. I recall one idea of terraforming the Moon and surrounding it with orbiting "shrouds", extremely large, thin transparent films that would knock any drifting gas molecules back towards the Moon and keep the atmosphere intact over geologic time ( assuming the system was maintained or self repairing ). It doesn't need to be anything like a solid bubble since the Moon can already almost hold an atmosphere.

If a big Moon is really too much for Earth to handle, one could postulate a self repairing artificial system like the one I mentioned above ( emplaced by some alien species billions of years ago ) keeping a real-world-sized Moon habitable. It would add the effects on society of having such large artifacts visible in the night sky to the OP's scenario though.

[Kuroneko]

You might be able to compensate for this by having the moon be farther away. I'm not sure how far away you can make it before it's no longer gravitationally bound to the Earth though.

I'm going to assume equal masses, so that the tidal effects are symmetrical. Tides scale as m/r³, and the the Earth is 81.3 times more massive than the Moon. Thus, we can have an Earth-sized object 81.31/3 = 4.33 times farther away and produce equivalent tides. The problem, however, is that the Hill-Roche sphere is 0.01AU, and this is just outside of it. Thus, such a configuration is unstable. Further, the H-R sphere is a bad approximation for comparable masses, so to be safe we should try for a retrograde orbit under half the H-R radius, which would produce tidal forces 11 times those of the Moon or more. Since it also scales as m1/3, this is independent of planetary mass.

That's probably not so bad; if both planets are smaller, larger tidal forces might actually be a good thing, in as much as they would increase geological activity and prevent the bodies from cooling too soon from their formation.

[Pablo Sanchez]

The moon would have to be much larger to be able to support life, so I'd have to ask any resident physicist/geologist whether a double-planet system of two earth-sized objects could result in both being capable of supporting life, or if the tidal forces at work would in some way prevent this.

I don't think this follows. Titan is only about double the mass of Luna, yet it has an atmosphere of about 1.5x Earth density at the surface. And certainly STP isn't necessary for intelligent life; La Rinconada, Peru has only about 63% sea level density, yet has some 30,000 inhabitants.

Don't both planets in a binary system tend to have a similar physical composition, because the stable orbital system between bodies of similar mass means that they must have formed around the same time from the same materials--or formed in the way that Earth and Luna did (Luna being ejected from the Earth by a massive impact). Since MJ said that the planet we're talking about was the Earth, specifically, I didn't read it as likely that the Earth could have possibly developed a satellite with a dramatically different composition from itself. Also, I'm pretty sure that a major reason that Titan maintains an atmosphere is it is much farther from the sun and consequently much cooler; if there was a similarly sized rocky-ice object 1 AU from the sun (as opposed to 9 AU!) I believe it would have boiled that water and atmosphere away because of the much greater energy input.

[Junghalli]

^ Actually, it occurs to me that in this scenario this "moon" might be Thea (the Mars-sized object that smacked into Earth to make the moon). In this scenario it might have been captured instead of impacting.

[Surlethe]

Also, I'm pretty sure that a major reason that Titan maintains an atmosphere is it is much farther from the sun and consequently much cooler; if there was a similarly sized rocky-ice object 1 AU from the sun (as opposed to 9 AU!) I believe it would have boiled that water and atmosphere away because of the much greater energy input.

Isn't Titan's atmosphere much heavier than Earth's, full of hydrocarbons and such? That might be another reason why it retains an atmosphere with lower-than-Earth gravity.

[Pablo Sanchez]

Isn't Titan's atmosphere much heavier than Earth's, full of hydrocarbons and such? That might be another reason why it retains an atmosphere with lower-than-Earth gravity.

According to what I can find online it contains hydrocarbons but is mostly (90%) nitrogen.

[Coyote]

I could see a number of effects on religion. If the Moon is full of plant & animal life, it could have the effect of boosting the idea that God has laid out a bountiful universe for us, and prop up the idea that we are special --and deserving.

A Moon with intelligent life, however, would possibly undermine that. I could see attempts to convert Lunarians or possibly even religious wars-- but no doubt about it, the religions of the world would have to accept that there will be others out there who don't see things the same way they do. It may make them more mellow and accepting, but the extremists will be pushed to super-extremism, I think, as they seek to crusade into the stars aganst the heathens.

[GrandMasterTerwynn]

Also, I'm pretty sure that a major reason that Titan maintains an atmosphere is it is much farther from the sun and consequently much cooler; if there was a similarly sized rocky-ice object 1 AU from the sun (as opposed to 9 AU!) I believe it would have boiled that water and atmosphere away because of the much greater energy input.

Isn't Titan's atmosphere much heavier than Earth's, full of hydrocarbons and such? That might be another reason why it retains an atmosphere with lower-than-Earth gravity.

As has been stated, it's mostly nitrogen. The chief reason Titan can hold on to such a dense atmosphere given the world's paltry gravity is because of where it is in the solar system. In other words, it's out so far that it's cold enough that the thermal velocity of Titan's atmospheric gasses is lower than its escape velocity.

[Samuel]

^ Actually, it occurs to me that in this scenario this "moon" might be Thea (the Mars-sized object that smacked into Earth to make the moon). In this scenario it might have been captured instead of impacting.

The problem is that screws up the Earth alot- we got part of our core from Thea, as well as alot of other material.

I could see a number of effects on religion. If the Moon is full of plant & animal life, it could have the effect of boosting the idea that God has laid out a bountiful universe for us, and prop up the idea that we are special --and deserving.

A Moon with intelligent life, however, would possibly undermine that. I could see attempts to convert Lunarians or possibly even religious wars-- but no doubt about it, the religions of the world would have to accept that there will be others out there who don't see things the same way they do. It may make them more mellow and accepting, but the extremists will be pushed to super-extremism, I think, as they seek to crusade into the stars against the heathens.

Or one God per world. How did the ancients think of the planets again? Did they think that the God it was named after was associated with it or was it just a name?

[Pablo Sanchez]

The problem is that screws up the Earth alot- we got part of our core from Thea, as well as alot of other material.

If the impact was more energetic, like if Theia had been larger and faster moving, could the objects resulting from the collision have been more nearly similar in size, rather than one being dramatically larger than the other?

[Coyote]

Post-impact Thea loops around, caught in the Sun's gravity, and-- by a twist of fate --get caught on th ereturn loop by the proto-Earth it once smashed, and the two settle into a coexistence... heh.

We'd have better luck imagining a habitable Venus and/or Mars, really. That would be cool.

[starslayer]

If the impact was more energetic, like if Theia had been larger and faster moving, could the objects resulting from the collision have been more nearly similar in size, rather than one being dramatically larger than the other?

As it was, the Theia/Earth collision was a very oblique impact. If you want the size disparity to be smaller still, though, the impact would have had to be almost literally a grazing strike. Theia cannot have moved much faster than it did simply because it shared Earth's orbit, and thus had its orbital velocity. If Theia had been larger, then there would have been more ejecta, and the Moon could possibly have been larger than it is.

[PeZook]

If the Moon is habitable, it has an atmosphere. If it has an atmosphere, we're not going there in the sixties - we barely managed to get a small return rocket there which would have no chance to reach orbit with an atmopshere present, not the mention descend: a LEM would have to carry a heat shield of its own and be capable of withstanding the forces of re-entry, probably as much as tripling its mass. No colonies for us, sorry, not even the Energia could deliver 45 tonnes to lunar surface.

[The Duchess of Zeon]

If the Moon is habitable, it has an atmosphere. If it has an atmosphere, we're not going there in the sixties - we barely managed to get a small return rocket there which would have no chance to reach orbit with an atmopshere present, not the mention descend: a LEM would have to carry a heat shield of its own and be capable of withstanding the forces of re-entry, probably as much as tripling its mass. No colonies for us, sorry, not even the Energia could deliver 45 tonnes to lunar surface.

We could assemble a lander in orbit from multiple launches, you know. Sea Dragon comes to mind as a rocket design that could be mass produced for the purpose of doing this.

[PeZook]

We could assemble a lander in orbit from multiple launches, you know. Sea Dragon comes to mind as a rocket design that could be mass produced for the purpose of doing this.

It would still have to re-enter, land gently, then take off and reach orbit entirely by its own, with no support infrastructure whatsoever. We could, maybe, do that in 1989, but definitely not in 1969.

[Fr33ze]

In both cases how would the existence of a habitable moon effect the development of human civilizations.

It also depends on how the habitants behave on the Moon, but on the top of my head it's as the following:

Changes * (environment + lunar calendar + women + ...) = ?

[Lord of the Abyss]

In both cases how would the existence of a habitable moon effect the development of human civilizations.

It also depends on how the habitants behave on the Moon, but on the top of my head it's as the following:

Changes * (environment + lunar calendar + women + ...) = ?

The moon doesn't actually affect women, you know.




Unless they're werewolves.

[Coyote]

A habitable Moon would have been deduced through observation well before we got to the point of trying to land; even if we hadn't figured it out, the first few fly-by probes would have told us what we needed to know. Knowing that the Moon was habitable would make it reasonable to push for an in-orbit build for a lander. Controlled crashes beforehand would give us data on whether or not parachute scould be used to control descent to the Moon.

More than likely, the Moon wouldn't be a lush garden; realistically a 'habitable' Moon would be one with a cold, thin atmosphere where at its lowest points would be like the highlands of Peru or possibly even higher --that point where oxygen masks aren't necessary if you're sitting around, but more than a few minutes of activity will have you gasping and reaching for an o-mask. The 'life' would probably be various lichens and extremophile stuff that can excrete oxygen while living in such an environment.

[Lord MJ]

We could assemble a lander in orbit from multiple launches, you know. Sea Dragon comes to mind as a rocket design that could be mass produced for the purpose of doing this.

It would still have to re-enter, land gently, then take off and reach orbit entirely by its own, with no support infrastructure whatsoever. We could, maybe, do that in 1989, but definitely not in 1969.

A habitable moon would result in much more effort putting into developing space technology than what has happened in real life. We may not have made it in 1969 but our rate of development would be accelerated relative to what is in real life such that 1989 space tech in the alternate reality is more advanced than 1989 real life space tech.