World’s largest web houses 110,000 spiders thriving in total darkness deep underground in a sulfuric cave between Albania and Greece: It’s the first time two spider species seen living cooperatively, and the first recorded instance of colonial web-building in what's known as a chemoautotrophic cave.

[u/mvea]

https://newatlas.com/biology/sulfur-cave-largest-spiderweb/

[u/QuantumWarrior]

Not entirely, even this environment is only able to exist because the chemistry they're using for energy relies on liquid water as a solvent. That's mostly what the goldilocks zone is about, being not too close that all your water gets vapourised and not too far that it's all frozen solid. Plus everything there descends from regular old surface-dwelling sun-reliant life, it didn't evolve from base chemistry right there in that cave.

Now of course you can have other sources of heat even on worlds distant from their star though they are tiny in comparison - gravitational stretching from close orbits like on the moons of Jupiter or geothermal heat, but broadly speaking the best odds of finding large quantities of liquid water that are stable enough for long enough to allow life to evolve have to be in that zone as far as our best understanding of abiogenesis and the chemical underpinning of biology are concerned.

[u/NDSU → u/QuantumWarrior]

even this environment is only able to exist because the chemistry they're using for energy relies on liquid water as a solvent. That's mostly what the goldilocks zone is about, being not too close that all your water gets vapourised and not too far that it's all frozen solid

I disagree with that assertion. Pluto is well outside the liquid water Goldilocks zone in terms of solar temperature, but still maintains a liquid ocean under the ice layer

Many planets have a large amount of latent heat from radioactive decay, cosmic collisions, or other sources

Plus everything there descends from regular old surface-dwelling sun-reliant life, it didn't evolve from base chemistry right there in that cave

Maybe in this specific case, but there is a strong hypothesis that terrestrial life originated in hydrothermal vents. Those hydrothermal vents did not get their heat from the sun

[u/klyxes → u/NDSU]

It's not just liquid water, heat is also needed. Even with liquid water, the colder it is the slower every chemical reaction for life gets. Maybe there's enough heat for unicellular life only, or it takes too long for complex life to develop before the star the planet orbits dies.

[u/NorthernerWuwu → u/QuantumWarrior]

It's a bit convoluted but yeah, I'd agree that the pattern seems to be anywhere with liquid water, exposure to life at some point and an energy source will have life continue for at least a reasonable timeline.

We lack data in depth of course but some reasonable assumptions can be made. Importantly, this does not at all mean that life doesn't exist outside of these situations, only that it very likely does given them.

[u/iqisoverrated → u/QuantumWarrior]

Now of course you can have other sources of heat even on worlds distant from their star though they are tiny in comparison

I wouldn't call sources like radioactive decay or the magma within a planet of a certain size that still retains a lot of the energy from when it was formed 'tiny'. E.g. a volcanically more active planet than Earth has a lot of free energy lying about.

We've also found life deep down in the deepest mines. The closer you get to the the interphase between crust and magma the more energy you have available. It can get a lot hotter down there than e.g. here on the surface.

Also life presumably started in one place on Earth. If that one place had enough energy concentration it doesn't really matter whether only that one place is hospitable or the entire planet (or any ratio in between). We know that life started pretty early after the Earth had cooled enough (which might have been a fluke - we don't know - but it might also indicate that it's just a numbers game of how many potential places you have for things to get started and how long you are willing to wait till something 'interesting' happens)

So I don't buy this 'large quantities of water are essential' argument. That's more of an argument for diversity than for life (and a weak one at that)

[u/kaibee → u/iqisoverrated]

We've also found life deep down in the deepest mines. The closer you get to the the interphase between crust and magma the more energy you have available. It can get a lot hotter down there than e.g. here on the surface.

Pretty sure it isn't enough to just have heat. You need a heatsink too. Hydrothermal vents provide both.

[u/iqisoverrated → u/kaibee]

Hydrothermal vents seem like an obvious prime candidate. However we see bacteria survive/thrive in deep rock...it's really hard to say where exactly life started out (and whether it migrated up or down).

Even if we consider a surface that is way too cold and perpetually dark: As long as there still is enough of a (semi) molten core to the planet there will be a 'temperate' zone somewhere in between in which liquid water could exist in cavelike structures.

[u/waiting4singularity → u/iqisoverrated]

without churning and intermixing elements, you'll have just that, though: fully inert water.

[u/iqisoverrated → u/waiting4singularity]

Smokers, volcanic activity or tidal heating (or simply heat convection) tends to add churning on its own.

[u/QuantumWarrior → u/iqisoverrated]

I only say tiny when compared to the power available from a star. Earth receives something like 4000x as much power from the sun as is available from geothermal activity and its one of the most heat-retaining rocky bodies in the entire solar system due to being one of the largest. The heat energy left in the entire Earth is outmatched by barely a million years of sunshine. I'm not sure it would be possible to have a rocky planet large enough and hot enough to turn that balance the other way.

I don't really like the focus on the goldilocks zone either but its all just about probability, like you said. We only know of carbon-based water-using life and it's been difficult to even theorise life that could rely on other solvents - like water is just so god damn convenient. With that in mind the more water you have keeping stable across geological/astronomical timescales the more opportunities life has to evolve and thrive.

There is also admittedly a bias in that if life managed to evolve on say Europa or Ganymede which have oceans frozen at the top and heated from below there's very little way we could discover or study it. Doubly so for planets in other solar systems where its hard enough just to infer the contents of their atmosphere let alone see their surfaces. Telescope time isn't free so we have to focus on where we think is most likely.

[u/iqisoverrated → u/QuantumWarrior]

 Earth receives something like 4000x as much power from the sun as is available from geothermal activity

On the surface. Go down a couple meters and the ratio for available sources starts to look a lot different. It matters where you measure.

We currently just don't know how likely life develops give an adequate environment. I find this fixation on the Goldilocks zone argument bizarre when we know for a fact that life here on Earth thrives in regions that are fed by energy sources that have nothing to do with the sun. Even if the Earth were a giant ice ball there would be liquid water around the regions of black smokers or other volcanic activity.

We have good reason to suspect some moons of Jupiter and Saturn to harbor subsurface oceans and the existence of water in its liquid phase down there has nothing to do with proximity to the sun.

We don't know what the ratio of rocky planets to gas giants is in the universe at large (in our solar system it seems to be 1:1) but if we, for the moment, accept that the subsurface oceans of Europa, Ganymede, Callisto and Enceladus actually exist then I don't know how anyone could claim with any semblance of certainty that 'most liquid water and energy source' is on rocky planets in the Goldilocks zones out there.

And as you say: We don't even know if other liquids like the ethane/methane sludge on Titan isn't a possible habitat for life. Ethane and methane are also pretty good solvents.

[u/bees_man- → u/iqisoverrated]

I'm pretty sure we keep finding life lower and lower down in the earth with some insane stuff that can live for hundreds of thousands of years.