The NASA exoplanet visualizer is very cool. Did not know about that. Thanks for sharing. I imagine those hypothetical visualizations will improve over time as our understanding of the exoplanet data gets better. It is amazing what you can derive from a single pixel of light.

Not sure why, but the visualizer is giving me a strong urge to boot Outer Wilds again.

Love that game

That’s an interesting exoplanet, though not sure how someone would live on a gas giant.

Maybe they don't. They might live on a rocky planet further out and just use TrES-2b as a place to run their solar farm because it's extremely close to their star and (due to being uninhabited) didn't have any NIMBYs opposing large-scale construction projects.

Note how far out from the planet's orbit NASA expects the habitable zone. We aren't very good yet at finding planets that aren't huge or nearly hugging their star, so there might be planets out there.

To be fair, if your solar farm can be in orbit around a planet that's not your legal address for tax purposes, it can just orbit the star?

Maybe building on the planet had some advantages during construction, like easier delivery or being able to use local resources. Or maybe the atmosphere helps with thermal management. Or being on a planet is useful for the infrastructure that does something with all that power (beaming it to other planets, producing solid, liquid or antimatter fuel for export, refueling space ships or robots, etc). Tax purposes. Diplomatic reasons, maybe there are established protocols for owning planets but large scale light blocking installations in orbit would upset a neighboring nation (though you suspect their opposition has more to do with simmering tensions over the Agreppo peninsula than with concerns about the impact on agriculture). There are plenty of plausible reasons, probably all wrong.

Could be legacy reasons. Maybe they initially built it around this planet, or maybe they’re from a moon in or it around it, and now it provides more than enough energy for their needs. I find people looking for aliens always expect them to be doing the most efficient thing and forgoing any semblance of history.

Aww man would be so cool to meet aliens and they show us around their stuff, and it all seems really dumb and convoluted, and they hate it too, but it would be too expensive to rip it all out and start over...

I don't think it makes sense for a humanoid species, but silicon based, perhaps? Iain M Banks' The Algebraist [0] has a near immortal species called Dwellers that manage it somehow :)

[0] https://en.wikipedia.org/wiki/The_Algebraist#:~:text=Dweller....

this is one of my favorites by Banks. Really mind-twisting.

In accelerando by Charlie stross, they live on raft that covers a large percentage of the planet's sky.

Presumably gas planets have a layer dense enough that a solid would float.

And not melt?

Maybe they live on a moon or two.

> My theory is that its darkness is down to the fact that the civilisation there has figured out a way to harness solar energy to near 100% capacity, along the lines of a Dyson sphere [1].

Very unlikely, in light of the fact that "the air of this planet is as hot as lava".

I wonder how temperature is measured for an object this far away. If it's calculated based on the expected energy absorption of a planet with this level of reflectivity, the measurement would be wrong anyway, assuming alien tech.

Instead of the energy being absorbed as heat by the planet, it'd instead be stored in some other form or used for interstellar travel, construction etc, right?

> I wonder how temperature is measured for an object this far away.

From the black body radiation spectrum.

[UPDATE] It turns out that the temperature of TrEs-2b is not directly measured, but extrapolated from other measurements (at least according to Wikipedia - https://en.wikipedia.org/wiki/TrES-2b#Temperature ).

> Instead of the energy being absorbed as heat by the planet, it'd instead be stored in some other form or used for interstellar travel, construction etc, right?

Yes, exactly. So the only possible impact of energy harvesting would be to make the planet cooler than it otherwise would be. How much cooler depends on the efficiency of the harvesting. But one way or another, an extremely hot planet is very unlikely to harbor an advanced civilization.

Theoretically a civilization that could capture 100% of the energy from it's star would be able to use however much of that energy it wanted to heat or cool the planet. They could make the conditions perfect for them. There could be a reason why they'd want the surface to be extremely hot.

This might be just the powerplant and they could be living somewhere else. A gas giant seems improbable as an advanced civ homeworld anyway.

There are no other discovered planets in the system, but perhaps there are some, or at least moons.

Isn’t that the expected outcome when energy production eventually outpaces the planet’s ability to dissipate energy into space?

No. The temperature of the atmosphere has nothing to do with whether or not aliens are harvesting the energy. At equilibrium, all of the incoming energy has to get radiated back out into space eventually whether there are aliens harvesting that energy or not.

The problem with an atmosphere hotter than lava is that very few materials are solid at those temperatures, and it's hard to imagine how a civilization could build an energy harvester without solid materials.

Those liquid green aliens are probably looking at us and going "how can life exist with so much matter in solid form and so cold”.

Well, they have a point. This is why the presence of liquid water on earth is a big deal.

But when the rocks start to melt you have problems.

Tungsten/Carbon based life forms? Solid when most everything else is liquid or gas.

It's very unlikely for life to arise under those conditions. To get life, you need to build a lot of random polymers in a short amount of time (relative to the age of the planet) and the only known way that can happen is in a liquid or a gas so you have diffusion working for you. But after that, to get technology, you need solids.

The good news is that you don't need to have the life arise under the same conditions that the technology exists. It's possible that the planet is inhabited by self-replicating tungsten-based technology that was created by life that arose somewhere completely different.

But the bad news is that we are much less likely to find the aliens than we are to find the descendants of the self-replicating robots they built millions of years ago. And the fact that we haven't found the robots makes it very likely that the aliens don't exist.

Secondarily, thermodynamics and other effects make many processes much less efficient at higher temperatures, examples including engines and solar panels.

They could be using iridium. When we're talking about aliens, we're already in the realm of hard-to-imagine, but it's worthwhile, I think.

Sure, energy in equals energy out at equilibrium, but another option is to have a steady state solution where energy is generated leading to potentially large temperature gradients.

Yes, that's possible. It could be that what we're looking at on the planet surface is the output of a huge planet-sized radiator, with a civilization living in air-conditioned comfort underneath. But the problem with that theory is that you can't actually use the whole planet as a radiator. You can only use the space-facing side. You have to use the sun-facing side for energy harvesting. That temperature gradient would show up in the spectrum, and AFAIK it's not there.

[UPDATE] I don't actually know if current exoplanet observing technology is capable of detecting such a temperature gradient, but given what I know we can observe I'd be a little surprised if it couldn't. A planet-sized energy harvester would make a pretty big dent in the passive thermodynamics, and detecting that should not be too hard. And it would be Really Big News.

This is a great video that touches on your point, the Earth must radiate the heat it receives to stay in equilibrium, even if it uses it to do work in the process.

https://www.youtube.com/watch?v=DxL2HoqLbyA

If we extract the maximum possible entropy of the incoming radiation wouldn't that mean we radiated at high-intensity but low-temperature?

What does that mean?

Everyday objects don't work like that. Saying ice cubes are cold is roughly equivalent to saying that they radiate less heat than the objects around them. If they radiated at "high intensity" then they wouldn't be cold anymore.

"A cold object that radiates heat at high intensity" is a contradiction.

Only for black body radiation do we have a perfect correspondance between spectrum and intensity. But there can be other ways of radiating. Non-black bodies. Antennas. Lasers.

Not even stars are perfect blackbodies.

The protomolecule was able to build structures on Venus. Then again, if your civilization was over a billion years old, all sorts of things might become possible.

That being said, it’s never actually aliens in astronomy. So far, anyway.

What would be an equilibrium if they spend collected energy on some process with low entropy output?

Like what?

I can't think of anything that would make a difference in the long run. Anything they do is still subject to the Second Law and the limits of Carnot efficiency. They can shunt a little bit of the energy off to the side and store it for a while, but it all has to end up as heat sooner or later.

Well, it's not going to outpace it, exactly. Unless the temperature is actually increasing (or decreasing), the energy in matches the energy radiated away, less the non-heat work.

> less the non-heat work.

Doesn't all the non-heat work eventually just become heat? Or am I misunderstanding your usage? Like a car with a solar panel still ends up radiating work as heat, by either air resistance (heat) or brake friction (heat).

That would be a strong alien to deal with 1.5 Jupiter gravity :)

> My theory is that its darkness is down to the fact that the civilisation there has figured out a way to harness solar energy to near 100% capacity, along the lines of a Dyson sphere

That doesn't work quite the way you think. If you harness all the energy your planet will start to glow, first red, then white. Eventually becoming as hot as your star, at which point you stop gaining energy.

Unless they are somehow converting that energy to matter, the laws of thermodynamics mean that all that energy eventually becomes heat.

Harvesting energy is a misnomer, what we want is the syntropy: the available work.

If we turned the Earth into a black body and used all Solar radiation to run computers or move stuff around at the theoretical limit, we'd still need the surrounding space to radiate off the heat as our cold well. So the temperature would be at whatever that equilibrium condition is, but wouldn't steadily increase. The equilibrium condition could be all over the place and would be largely determined by the composition of the atmosphere.

For the record I'm not in favor of paperclipping the planet like this. If anyone was wondering.

>If we turned the Earth into a black body and used all Solar radiation to run computers

>For the record I'm not in favor of paperclipping the planet like this. If anyone was wondering.

We should do this with Venus instead. It isn't doing anything useful at the moment, and is closer to the Sun than Earth. Mercury might be easier though.

Take incoming energy and make antimatter. Store for use outside of the sphere. That will be my premise for the book I am writing. ;)

Make equal amounts of matter and antimatter (you would have to anyway) and store them together in some kind of sealed power-unit.

Like Starget ZPM.

Nope, we are alone....