That'd make for a good story setup: aliens park a shadeship (c) at L1 and wait. They block out most but not all of the sun. After some time (months? years?), conditions on Earth become unbearable, so earthlings have to mount an attack.

Kind of like the movie Sunshine, but with more believable physics.

Edit: as a bonus, it could take place in ~50-100 years, when global warming has gotten worse. The aliens could disguise their motives for a while, claiming to be there to help counteract global warming. Warnings from a lone scientist would be ignored. Then, as things start getting too cold, their true purpose would become clear to all.

> The aliens could disguise their motives for a while, claiming to be there to help counteract global warming.

Seemingly benevolent aliens just here to help us fix our mess, but ultimately just want to sneakily take our stuff, is fun trope. https://www.gateworld.net/sg1/s4/2010/

"To Serve Man"

Or maybe they showed up 200 years ago and thought: this is a very nice planet, except it's a bit too cold. What can we (compel the natives to) do to make it some 6 degrees warmer on average so that it is perfect for us? And the rest is history.

This is kind of the plot of Pacific Rim. The aliens originally invaded in prehistoric times, but then the Earth cooled and they had to retreat to their dimension. Humans then warmed it back up so they could restart the Kaiju invasion plans.

Who would like to do the math on how big the shade would need to be and how long it would take to reach a tipping point?

Love this idea for a story.

As an alternative - it could be the oil producing countries, not aliens - seeking shade earth to disrupt solar and wind energy, and return to oil dominance.

Slow down there, Mr. Burns.

This sounds more like something out of a Mad Max type universe rather than sci-fi. A world living off fossil fuels because daylight has been reduced to 10% of the normal duration or something like that.

Or the "water company" from Tank Girl - blocking the sun to drive up revenues for the oil/coal companies.

Nah, you just need a simple Bond Villain Plot.

Step One: build a machine that can cool the Earth, solving global warming Once and For All.

Step Two: demand the governments of the Earth pay you $1 trillion to turn it off at the appropriate time.

I mean, a trillion dollars to solve global warming sounds like a pretty good deal to me?

That would be a good ending. The villain suddenly becomes the hero, but his evil purpose disappears and he gets depressed. :)

and then he proceeds to train ChatGPT5 with given money, even though it wasn't $7T he was hoping for.

It's not solving if they can turn it back on, it's a subscription. The elite want renters, 'you will own nothing and be happy'.

It should give people pause that with all the push for more renewables in California and Germany, they now have among the most expensive electricity on Earth.

You're conveniently leaving out that, at least for Germany, this was already the case before.

Shit, I think the US spent several times that per year, without even a good plan to pay it back. Does that mean the United States is irresponsible, or the amount is just so trivial they can't be bothered? Who cares, it's some other administration's problem.

Solving global warming, turning off the earth iceball machine when it's time? Easily worth $100 trillion. OP just has no supervillain potential.

"I demand the sum of... $1 million dollars!" -- Dr. Evil

Also sharks, with friggin lasers attached to their heads.

And countries which use reliable sources of energy like nuclear would be unaffected. How curious...

Perhaps building unreliable energy infrastructure dependent on favorable climatic conditions is not the greatest idea. Especially if there's going to be major climate change. How's Germany doing again with all its solar lol.

Well, if Exxon builds a space ship…

Alternative, more physically feasible attack—-aliens take over the moon and begin pushing it closer, messing up tides/weather etc. Humans are forced to fight to take back the moon

Shifting the orbit of the moon is more believable? Than placing a mega structure at L1 (which despite being mega, would be orders of magnitude less mass than the moon)?

So. That sounds like an idea for a sequel to Iron Sky. But with Space Aryans™! and not space aliens.

> They block out most but not all of the sun.

Interesting to think about:

  * How much mass could be positioned at L1 before changing the gravitational proposition of L1?
  * How large an object could be positioned at L1 before it exceeded the practical bounds of L1?
  * Presumably the object would reflect rather than absorb solar radiation. How would it deal with other solar ejecta?

An embargo on light.

>The aliens could disguise their motives for a while, claiming to be there to help counteract global warming. Warnings from a lone scientist would be ignored.

It's a cookbook!

Humans are so suspicious. The title is actually "How to Cook for Humans".

The most unbelievable part of this would be that earth cooperates enough to organize an attack. Seems more likely countries will use the opportunity to attack each other. In the end, the aliens should win. A few straggling survivors might see the ships land on Earth to survey the conditions.

Another good story setup involving aliens: aliens pop by, tell us we have 25 years to "get our shit together, and the ambiguity here is deliberate, humans" on this planet, or we will be garbage collected.

Then they come back a year later: "I have bad news: the timeline has been accelerated, you now have 10 years".

What to do? To whom shall we turn for a plan?

> Warnings from a lone scientist would be ignored.

A good movie plot, but I imagine in reality it would be obvious from the start that this would be a possibility and no scientists would be caught off-guard when the shade just didn't get removed. I can be almost certain as well that large factions of humans would "know" (believe, based on no facts) that is was happening all along and there would be incredible conflict across Earth as we figured out how to deal with this gentle attack, even before it was certain that is was an attack.

> even before it was certain that is was an attack.

If it was done without consent, then it is an attack, and it doesn't fu*cking matter whether it ends up causing physical harm (or even if the invaders genuinely thought they meant well).

Regardless of whether it ends up taking away somebody's sunlight forever, it's still robbing people of all their agency. That decision was never theirs to make.

this is such a good idea for a movie

This reminds me of the game "SPORE" in the last stage, you flew around in a spaceship conquering planets. The game had a balance problem, but while the space combat was difficult - it was rather easy to fly around a planet really quick "Terraforming". Remove the entire atmosphere, then add the atmosphere back and plant a colony.

As a bonus, the other aliens in the game didn't view destructive terraforming as equivalent to WMDs - you could do this without even declaring war.

That sounds like a great idea for a sci-fi novel, but before I steal and write it I thought I'd ask ChatGPT if it already exists, and it seems it does.

"The Forge of God" by Greg Bear The Makers deploy a vast, self-replicating robotic spacecraft called the "Doomsday Rock" near Earth's sun. The purpose of this massive construct is to absorb energy from the sun, causing it to dim and ultimately leading to the freezing of Earth, thus rendering it uninhabitable.

That’s not the plot of The Forge of God. Maybe it’s some other novel, but definitely not the Forge of God.

Spoiler alert: in The Forge of God the Earth gets literally blown to pieces.

I wonder how that would look from a feasibility perspective...

Let's see - Earth's radius is 6,378 km.

Area exposed to the sun therefore would be 6,378 * 6,378 * 3.14 = 127,731,695 [1]

If you wanted to block just 1% of the light, that would take a shade of 1 million square kilometers, which would be equivalent to a shade that is 1,130 km on a side.

Seems like it would be tough to do given all the dust and rocks floating around the sun. Also, you're only covering 1%, which is much less than cloud cover.

I'd assume you'd aim to block at the equator since that would have the most direct impact on the intensity of the sun over the course of a year.

[1] - I'm calculating the projection as a flat surface here, so the numbers aren't exact but close enough.

Interesting. That area would be roughly one million Sunjammers[1]. One Sunjammer is 1200 m^2 and wights 32 kg. To lift all this would be 32 million kg or 32000 tons. One Starship launch is designed for 250 metric tons when expendable so it would take 128 launches. Add in some fudge factor for orbital burns and I figure 150 launches would do it. Doesn't seem insurmountable.

Edit: Seems I misread the Starship capacity. This is probably only to LEO. Its hard to estimate but going by the geostationary payload, it would be one third of that, so triple the amount of flights. At a cadence of 2 launches per week it would take 4.5 years to launch all of it. ( 450 launches / 2 launches per week / 50 weeks a year)

1. https://en.wikipedia.org/wiki/Sunjammer_(spacecraft)

If you are clever with cabling through your shade and launch in the right orbit you can use the Earths magnetic field to keep the things oriented properly. Astronomers would hate you though.

I'd guess it would be far more efficient to launch more of these into regular orbit than trying to assemble them out in L1 and keep them from drifting off, even though you would need to launch at least twice as many for the same amount of coverage.

1 million square kilometers is 1 trillion square meters, or 833 million Sunjammers. It would take 3748 years to launch them at 2 Starship launches per week.

Does it have to be a sheet of material? If all we want to do is shade the earth, we could launch a few million KGs of glitter into low earth orbit or to the Sun-Earth L1.

They would attract each other and clump into a loose ball.

Probably only over thousands or millions of years?

>Seems like it would be tough to do given all the dust and rocks

I wonder if there's a solution that uses the dust and rocks. Maybe you nudge some near-Earth asteroid near L1 and then blow it up or something.

To provide full Sun shade, the shield should be at L1. and it should have the same angular size from Earth as the angular size of the Sun

> and it should have the same angular size from Earth as the angular size of the Sun.

Technically you need a bit more than that, for its umbra to block out the entire photosphere over the entire Earth:

https://en.wikipedia.org/wiki/Tangent_lines_to_circles#Outer...

"Just parking" between would not be possible without putting really a lot of energy into maintining the position of the shade. Due to orbital speed differences depending on the distance to the sun[1] and the pressure of the light[2] and solar wind[3] on the shade and Earth's gravitational interference. And the shade must be very much larger in diameter than the planet in order to cover it. How large depends on the distance from the planet.

[1] See https://en.wikipedia.org/wiki/Orbital_speed#Planets

[2] See https://en.wikipedia.org/wiki/Radiation_pressure

[3] See https://en.wikipedia.org/wiki/Solar_wind

You would want to place it slightly on the sun side of the L1 point, where gravitational and solar wind forces cancel out.

Or you could just smack it with a really big rock. That nicely sterlizes the planet too, so you can reseed it with life from your planet after to make it more comfortable.

Honestly it's all kind of silly because distances are so vast. It makes little sense to travel to a distant star - much better to build space habitats in your own star system. And even if you were going to do that for some crazy reason, there's no shortage of uninhabited planets out there. There's no need to commit planetary genocide of an alien race. Also if you have that kind of tech level, space habitats make more sense than planets anyway. Finally if you seed distant star systems with your own species, you risk that species going to war with you later (see how that played out on Earth just across the oceans.)

I was thinking the deep freeze might be useful in preserving some potential food sources, assuming it happens quickly enough. But I agree sterilizing the planet provides some advantage as well.

Aliens probably would not be able to eat Earth life.

You are correct, but it's capitalism and the adrenaline kick. We are culturally conditioned folk, and all scripts about alien invasions that end up in movies follow a completely implausible scenario. Most don't even bother any longer to give a reason for invasion. I would blame the writers of those scripts, but movies without violence don't give the adrenaline kick and don't sell well.

Here is an idea for any writers reading this who want to break the violence cycle: whenever you feel you need to have a character kill another in a gratuitously violent way, twist the plot so that they instead end up having steamy sex. The readers will get an intense hormone rush that way too.

American viewers love gory violence, but get offended at steamy sex scenes. That makes no sense to me.

Ahh yes famously American media like Squid Games and Alice in Borderland are so filled with gory violence I can barely handle it. And American movies are famous for having so few steamy sex scenes in them that people are not constantly rolling their eyes at the “sex sells” mantra to explain their frequency.

> a really big rock ... nicely sterlizes the planet

Have you seen Earth? We've been hit with a big rock, we've turned out atmosphere into poison, and had several other mass extinctions, none of which sterilized the Earth.

Unless you mean a Theia-level rock to turn the entire surface into lava, but you risk changing the mass, composition, and satellite system of the planet. At that point it's a different planet entirely, so I don't know why you would expend all that energy. Just find another planet to live on.

It came pretty close, remember life slowly bounced back afterward. Something a little larger would almost do the trick. You just clean up what survives.

No I don't think it did. I'm not sure you're understanding the scale of things here. I don't believe it came close at all, if "close" means that a ground team could have sterilized the planet afterward. Even if 99% of life were destroyed, that doesn't mean there's one little tide pool with some barnacles surviving, that means there's extremely hardy single-celled organisms living in the deepest nooks and crannies all over the planet.

We can't even "just clean up what survives" in the cleanest rooms on Earth, using techniques specifically intended to do that. Life is incredibly tenacious, I really don't think you're going to wipe it off a planet's surface without destroying the surface (and atmosphere, probably) of the planet in the process. And if that's acceptable - again, why wouldn't you just pick a barren planet.

> Honestly it's all kind of silly because distances are so vast. It makes little sense to travel to a distant star - much better to build space habitats in your own star system.

Maybe their own star system is not safe for them. Say a political or religious minority that the majority would like to exterminate.

> And even if you were going to do that for some crazy reason, there's no shortage of uninhabited planets out there. There's no need to commit planetary genocide of an alien race.

If they've got cheap and easy FTL, sure. But suppose they don't have FTL. They are going the slow way, using a generation ship. At launch they may only know that their destination has a habitable planet but not know if it has intelligent life already.

Their generation ship environment might not be reliable enough for them to want to risk trying to move on to another star if it turns out the first habitable plant already has intelligent life.

Better than nuclear weapon, no nasty fall out. Better than death star, you still have a planet afterwards.

If they had made the death star bigger, they could have done this tbh.

Wouldn't moving the death star closer to the sun sort that out ?

Closer to the star would only help if the star's size was similar to the death star. And if the death star was made larger then it wouldn't be mistaken for a small moon.

Too expensive!! Stratospheric aerosol injection are way cheaper!

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

Reminds me of this HN story from yesterday:

https://news.ycombinator.com/item?id=39361279

What if the aliens already set the snowball on this planet and haven't come back yet

What if we are the aliens and have been back for millions of years?

Have you done the calculation how much material is required for such an endeavor? I bet there are more cost effective approaches.

It doesn't have to be very thick at all. Harder part would be to keep it in place, as it would act as a sail.

Okay, like what exactly?

"You're in the way of a construction project, sorry, but please evacuate the planet". The fake notice costs you next to nothing.

"The plans for demolition have been available on Alpha Centauri which is only 4 light years away you know."

I like the idea of the solar system getting eminent domained for a scifi

Here you go: https://en.wikipedia.org/wiki/The_Hitchhiker%27s_Guide_to_th...

This is literally the plot of Hitchhiker’s Guide to the Galaxy. It’s a great read.

This is dangerous talk. Aliens might be crawling HN and feed their AI models to find our weak spots! Beware.

No worries there - their AIs will spin them hallucination-riddled nonsense, just like our do.

> Have you done the calculation how much material is required for such an endeavor?

It's a tiny fraction of what's required for a proper Dyson sphere. And we know civilizations can afford those because we can no longer see their stars.

For anyone who's hung up on saving nickle, we could do a low budget Worldring² or even thriftier Shadow Squares®.

     ²Nivenlarry  ®Larry Niven

> And we know civilizations can afford those because we can no longer see their stars.

That's a giant claim you just made like it's fact.

> That's a giant claim you just made like it's fact.

You are correct. That is absolutely a thing I did.

But it doesn't make any sense, given we do not have good evidence of alien civilizations, not to mention Dyson spheres.

> But it doesn't make any sense, given we do not have good evidence of alien civilizations, not to mention Dyson spheres.

Also correct. Even past that, we haven't been mass-cataloging stars long enough for a Dyson sphere to be constructed and remove a star from our view.

So why make the initial claim "And we know civilizations can afford those because we can no longer see their stars."? Is it humor or irony I'm missing?

The absurdity of it makes me happy.

Fair enough. Poisoning the well for giggles.

> Fair enough. Poisoning the well for giggles.

One man's poison is the same man's alcohol and mankind revolves around that.

It is especially big claim because there have been recent searches for Dyson Spheres and none of have been found. I think the Gaia spacecraft covered most of the visible half of the galaxy.

Dyson Spheres would be really obvious, emitting infrared radiation unlike normal stars.

I really liked Pandora's Star (The Commonwealth Saga) by Peter F. Hamilton.

> I really liked Pandora's Star (The Commonwealth Saga) by Peter F. Hamilton.

It looks promising; I'll check it out. Appreciate the recommendation.

Currently reading that. And I am trying like hell to figure out how all of the different stories will come back together.

Oh you are in for a treat. They don't fully finish in that book, for the conclusion you need high-octane Judas Unchained with the best inter- and then planetary chase scene. A great book with lovely twist in the end.

The flaw with your theory is Dyson Spheres don't hide the star. They convert visible light into infrared light. No energy conversion is perfect and always produces waste heat. Dyson Sphere basically looks like a really large star.

The infrared star stands out because it is different than normal stars.

> The flaw with your theory is Dyson Spheres don't hide the star. [follows with sound reasons]

These are really good points. I figured the flaw in my theory is we haven't had precision observation long enough for DS to get constructed. Also that if we noticed the disappearance of a star, that we'd attribute it to a DS and not some natural occluding object.

You have to make sure it doesn't drift away from the Langrange point, which is unstable…

Well, assuming an alien species that can deal with interstellat travel I am sure they can figure out a way to stay at a lagrange point.

What do you mean it's unstable? You orbit the Lagrange point, right? Sure you might have to spend some fuel maintaining the orbit, but we have a bunch of spacecraft at Earth sun L2 doing that just fine (e.g. the Webb). Is L1 less stable than L2 for some reason?

edit: SOHO is at L1

They tried that with the moon but parked it in the wrong spot.

“space toupee”

Sure if you've got unlimited time

I can’t believe I remember this. You jogged an old memory of Angry Beavers loose. IIRC in one episode they were tasked to save the day Armageddon style but started getting pulled into the sun because they strayed too far into its gravitational field and couldn’t boost out. So the beavers went out and built a dam in space to block it, which saved them but then Mission Control calls them up and says they’ve launched a new ice age.

This is all from memory and frankly I’m finding it fun trying it recall it without confirming it haha

Any sentient species that can generate, store, and then convert the amount of energy to either move a sunshade or move the infrastructure needed to construct and then deploy a sunshade at the distances needed to reach inhabitable worlds no longer cares about planets.

They can use that same technology to create, on a whim, inhabitable structures of arbitrary size and composition around any star- converting gas giants (or gas clouds or the solar winds) into perfectly positioned and constructed habitats in ideal locations.

Competition over planets would probably be as foreign and incomprehensible to them as what occurred in the universe prior to the Planck epoch is currently to us.