Could we survive without the sun?

[SLD]

OK. Here's a crazy question. I know most people think that it's insane to even consider that we could survive without the sun. But of course interstellar travelers do it all the time - at least in fiction if not real life. So that had me thinking if we could find another energy source sufficient to power life on the planet if the sun were no longer around. That may seem bizarrely hypothetical but what got me interested in the problem more seriously was a news report that we recently had a "close encounter" with another star. By recent, I mean only in the last 70,000 years. Here's the article if anyone is interested: https://www.popularmechanics.com/sp...000-years-ago-may-have-sent-comets-flying-in/

In that situation, the star passed into our outer Oort cloud and sent comets our way (possibly triggering a near extinction event?). So I thought, what would happen if a star came really close to our system such that it flung us out of orbit - either far out into the solar system, or even out of the system altogether. While that sounds drastic, we would have plenty of warning time. We would see the star coming probably thousands of years ahead of time. Say ten thousand. If we had ten thousand years to prepare, what could we do?

First we'd have to recognize that the atmosphere would freeze. So we'd have to find a way to tunnel deep in the earth and possibly use geo thermal heat to melt and vaporize the atmosphere at that level. We'd have to find a way to construct habitats that could survive. What if we had fusion power? Could we generate enough power to sustain an agricultural system for our food supply? We'd need artificial light, but that's not too hard.

it seems to me that with a ten thousand year lead time, we could engineer a solution. The problem would be what actually getting people to set aside their differences and work on the problem for thousands of years. Thoughts?

SLD

 

[bilby]

No need for fusion power; fission power will do just fine.

You could probably arrange for a sustainable environment with artificially lit farms, all powered by a few nuclear reactors, to support a few thousand, maybe tens of thousands, of people per facility.

I doubt you could keep too many millions, much less billions, alive though - probably the biggest challenge would be setting up such a facility, without the hordes of people who don't have a refuge destroying it. That might be a problem that could be mitigated by strict control on birth rate prior to having to go into the shelters.

The ability to obtain fresh resources once the atmosphere has frozen would be an issue - anything you can't dig to, you probably can't obtain at all. There's the potential for all kinds of nasty social problems too.

I don't see why (if it could be done at all) it couldn't be done in a century or less. I can't see a need for thousands of years of preparation.

 

[braces_for_impact]

I would think with a 10,000 year lead time we would find a new planet to inhabit rather than try to stay. I suppose we could use geothermal energy for awhile, but I don't see that being able to support high population levels.

 

[Jobar]

The Earth's core is kept molten by radioactive heat, and has nothing to do with the sun. So tunnel deep enough, and you could stay warm.

But living such a subterranean existence might be impossible over the long term. We'd have no natural survival options if our social/technological systems ever broke down. We'd definitely have to evolve into a much different species, I expect.

 

[bilby]

I would think with a 10,000 year lead time we would find a new planet to inhabit rather than try to stay. I suppose we could use geothermal energy for awhile, but I don't see that being able to support high population levels.

Where would we find a new planet?

About the only possible candidate is Mars, and frankly you are probably better off on an Earth that is rapidly departing from the sun's 'goldilocks zone' than on Mars - even assuming that Mars ain't also heading out of the Solar System.

Tens of thousands of years isn't enough time to establish the ability to travel to another solar system. Not in numbers sufficient to be a viable population, and with all the resources we would need.

Sticking with the Earth means hanging on to a vast supply of oxygen, water, and minerals - not to mention real estate. Farms take up a lot of room, and planets have room while spacecraft don't.

Essentially the OP scenario makes Earth a giant interstellar spacecraft. Launching a man made spacecraft from that Earth is just an excercise in throwing away 6x10²⁴kg of useful stuff, at great expense and for no benefit.

 

[repoman]

In 600 million years there will be no existing with the sun, except for an advanced civilization.

 

[lpetrich]

 Geothermal gradient -- the temperature gradient near our planet's surface is about 25 - 30 C / km. For a surface at 0 K and constant thermal conductivity as a function of temperature, that means a depth of 10 - 12 km to reach room temperature (20 C or 68 F)

1.2 Low Temperature Properties of Materials -- thermal-conductivity graph is at PDF page 28 out of 53. The closest thing to rock is quartz glass, and its thermal conductivity does not decline very fast with temperature.

(heat flux) = (thermal conductivity) * (temperature gradient)

So a constant heat flux with a lower thermal conductivity means a higher temperature gradient.


So far, the deepest mines are the TauTona and Mponeng gold mines in South Africa, at about 4 km, and the deepest drilled hole is the Kola Superdeep Borehole, at a little over 12 km. The mines and the borehole are limited by temperature, and a cold surface means that one may be able to go much deeper.

 

[Peez]

 Geothermal gradient -- the temperature gradient near our planet's surface is about 25 - 30 C / km. For a surface at 0 K and constant thermal conductivity as a function of temperature, that means a depth of 10 - 12 km to reach room temperature (20 C or 68 F)

1.2 Low Temperature Properties of Materials -- thermal-conductivity graph is at PDF page 28 out of 53. The closest thing to rock is quartz glass, and its thermal conductivity does not decline very fast with temperature.

(heat flux) = (thermal conductivity) * (temperature gradient)

So a constant heat flux with a lower thermal conductivity means a higher temperature gradient.


So far, the deepest mines are the TauTona and Mponeng gold mines in South Africa, at about 4 km, and the deepest drilled hole is the Kola Superdeep Borehole, at a little over 12 km. The mines and the borehole are limited by temperature, and a cold surface means that one may be able to go much deeper.

A cold surface also means a nice temperature gradient for geothermal electricity generation. The most obvious challenges would be oxygen and food generation as well as disposal of carbon dioxide and other wastes. Happily these may be addressed together with a little light, which can be generated from electricity. More complex problems would involve rare materials, energy for processing of materials, social engineering, and whether or not Fallout New Vegas should be required for everyone.

Peez

 

[SLD]

 Geothermal gradient -- the temperature gradient near our planet's surface is about 25 - 30 C / km. For a surface at 0 K and constant thermal conductivity as a function of temperature, that means a depth of 10 - 12 km to reach room temperature (20 C or 68 F)

1.2 Low Temperature Properties of Materials -- thermal-conductivity graph is at PDF page 28 out of 53. The closest thing to rock is quartz glass, and its thermal conductivity does not decline very fast with temperature.

(heat flux) = (thermal conductivity) * (temperature gradient)

So a constant heat flux with a lower thermal conductivity means a higher temperature gradient.


So far, the deepest mines are the TauTona and Mponeng gold mines in South Africa, at about 4 km, and the deepest drilled hole is the Kola Superdeep Borehole, at a little over 12 km. The mines and the borehole are limited by temperature, and a cold surface means that one may be able to go much deeper.

But you can’t go deeper until you’re forced to and then it may be too late.

SLD

 

[Elixir]

Farms take up a lot of room, and planets have room while spacecraft don't.

Meh. Can you say "Ringworld"?

Ringworld parameters
Radius 9.5×107 miles (~1.5×108 km) (~1 AU)
Width 997,000 miles (1,600,000 km)
Height of rim walls 1,000 miles (1,600 km)
Mass 2×1027 kg (1.8×1024 short tons) (1,250,000 kg/m², e.g. 250 m thick, 5,000 kg/m³)
Surface area 6×1014 sq mi (1.6×1015 km²); 3 million times the surface area of Earth.

 

[steve_bank]

No sun, no photosynthesis, no oxygen.

The closed system tried in 70s/8os, Biosphere, failed.

 

[Loren Pechtel]

Farms take up a lot of room, and planets have room while spacecraft don't.

Meh. Can you say "Ringworld"?

Ringworld parameters
Radius 9.5×107 miles (~1.5×108 km) (~1 AU)
Width 997,000 miles (1,600,000 km)
Height of rim walls 1,000 miles (1,600 km)
Mass 2×1027 kg (1.8×1024 short tons) (1,250,000 kg/m², e.g. 250 m thick, 5,000 kg/m³)
Surface area 6×1014 sq mi (1.6×1015 km²); 3 million times the surface area of Earth.

Can you say "unstable"?

How about "unobtainium"?

- - - Updated - - -

No sun, no photosynthesis, no oxygen.

The closed system tried in 70s/8os, Biosphere, failed.

Doesn't mean it can't work, just that one poor attempt failed.

 

[bilby]

Farms take up a lot of room, and planets have room while spacecraft don't.

Meh. Can you say "Ringworld"?

Ringworld parameters
Radius 9.5×107 miles (~1.5×108 km) (~1 AU)
Width 997,000 miles (1,600,000 km)
Height of rim walls 1,000 miles (1,600 km)
Mass 2×1027 kg (1.8×1024 short tons) (1,250,000 kg/m², e.g. 250 m thick, 5,000 kg/m³)
Surface area 6×1014 sq mi (1.6×1015 km²); 3 million times the surface area of Earth.

OK, I stand corrected. Planets have room, while spacecraft we could actually build don't.

For a start, we are three orders of magnitude short in raw material tonnage, even if we used up our entire planet.

 

[Jokodo]

OK. Here's a crazy question. I know most people think that it's insane to even consider that we could survive without the sun. But of course interstellar travelers do it all the time - at least in fiction if not real life. So that had me thinking if we could find another energy source sufficient to power life on the planet if the sun were no longer around. That may seem bizarrely hypothetical but what got me interested in the problem more seriously was a news report that we recently had a "close encounter" with another star. By recent, I mean only in the last 70,000 years. Here's the article if anyone is interested: https://www.popularmechanics.com/sp...000-years-ago-may-have-sent-comets-flying-in/

In that situation, the star passed into our outer Oort cloud and sent comets our way (possibly triggering a near extinction event?). So I thought, what would happen if a star came really close to our system such that it flung us out of orbit - either far out into the solar system, or even out of the system altogether. While that sounds drastic, we would have plenty of warning time. We would see the star coming probably thousands of years ahead of time. Say ten thousand. If we had ten thousand years to prepare, what could we do?

First we'd have to recognize that the atmosphere would freeze. So we'd have to find a way to tunnel deep in the earth and possibly use geo thermal heat to melt and vaporize the atmosphere at that level. We'd have to find a way to construct habitats that could survive. What if we had fusion power? Could we generate enough power to sustain an agricultural system for our food supply? We'd need artificial light, but that's not too hard.

it seems to me that with a ten thousand year lead time, we could engineer a solution. The problem would be what actually getting people to set aside their differences and work on the problem for thousands of years. Thoughts?

SLD

I'm unsure about the ten thousand years lead time (if it's a star - yes, but for a rogue planet or brown dwarf, not so much). Fairly large objects can still hide in our backyard:  Planet_Nine is suspected to have around ten earth masses + and to reside in an orbit with a semi-major axis of 700 AUs -- and the fact that we haven't spotted it doesn't count as an argument against its existence: We wouldn't expect to spot it at that distance. 700 AU may sound like a lot, but it's only 1e14 metres. Now if we're talking about an object exterior to our solar system, those tend to have high relative velocities  ʻOumuamua had a relative velocity of 26 km/s before being accelarated by the sun, and that's actually within the typical range for nearby stars with similar histories. Halo stars crossing the plane of the Milky Way can have relative velocities up to 200 km/s and more.

If we take 30 km/s as the likely initial velocity of our intruder, it'll only take it 3.5e9 seconds to get from where we wouldn't expect to spot it to here. That's 110 years and 11 months, and that's before we take into account that it will be accelerated on approach.

The second reason we might not is that just spotting it isn't enough to predict we'll be flung out of the solar system. Even with a much larger intruder, most encounters would be rather boring. 9x% of the time, a bypasser with even 0.1 solar masses that passes right through Earth's orbit will at best fling Mercury into a Venus-crossing orbit and destabilise the asteroid belt. In order for any planet to be actually flung out, the encounter must be very close indeed. So even if we spot a massive object heading right at the inner solar system, we'll have to wait until it's much closer and our observations concurrently more precise before we could wager a guess at whether it might actually kick us out.