What cosmological event could snuff out the sun without destroying Earth?

mfb

The issue is not the heat generation, but the general management with radioactive stuff and so on. RTGs might work, I would try to build them with long-living material on the surface.
That is the issue. Sun gives us free ~100-500 W/m^2, averaged over a year and depending on the position and weather conditions.
Wheat production is ~1000tons/(km^2 * year), therefore it gets 3GJ/kg of light (here I used 100W/m^2). This can be improved, of course, so maybe we can assume 1GJ/kg. Light generation is not 100% efficient, but the solar spectrum is not ideal for wheat growth, so this should cancel in some way. 1GJ is 280kWh, if you would have to pay for this wheat would be very expensive, even with current power plants.
Ok... do not use wheat for food production ;).

Fun fact: They work even better without the sun, as the surface is now a cheap and very cold reservoir. And they will continue to be possible for a few billion years.
Water: Recycling. Make your complete system water-tight, and recycle everything. The ISS already uses this.

CCWilson

I wonder how fast the temperature would drop as the Earth leaves the solar system - maybe not as fast as we'd think. All that heat stored in the core would continue to warm the planet's surface for millions of years and therefore also the atmosphere, with greenhouse gases holding the heat in. So cold as hell, but probably not cold enough to freeze oxygen and nitrogen for a long, long time. A lot would depend on whether carbon dioxide and methane and other greenhouse gases would stick around. How long, I wonder, could people walk around without space suits, wearing the kind of clothing climbers of Everest use?

Ryan_m_b

This wiki page might help, especially the information regarding the head content of the Earth and the fact that the majority of heat comes from radioactive material.

onomatomanic

I did some back-of-the-envelope seasonal temperature modelling recently, which I think should work for this case.

• If I simply switch off the Sun and neglect internal heat completely, the (global average) temperature drops below 200K after about 10 weeks and below 100K after about 30 weeks.
  
  
• If I make it slightly more realistic by sending Earth directly away from the Sun with the same speed at which it orbits now, the temperature drops below 200K after about 20 weeks and is still a little above 100K by the end of the first year.
  
  
• I have a dim recollection that the equilibrium temperature of Earth due to internal heat alone would be about a tenth of its present value, i.e. around 30K. If someone could confirm or correct that value, I can incorporate that into the model.

According to the wikipedia pages, the melting and boiling points of both nitrogen and oxygen lie between 50K and 100K, for preliminary reference.

CCWilson

In a novel I've started, the Earth has been flung out of solar orbit and is chilling down. Eventually it gets cold enough to freeze the component gases of our atmosphere. Anyone know what frozen oxygen and frozen nitrogen are like? Would they be more snow-like or ice-like? Among the significant components of the atmosphere, water vapor would obviously freeze first, then carbon dioxide, then argon, oxygen, and nitrogen. I'm trying to find out what the surface of the Earth would be like at the point that all the atmospheric gases froze. Would there be a layering of the frozen gases, or intermixing? Any idea what the texture of the icy covering would be - slushy, rock hard, snowy? And I'd appreciate any help in figuring out how deep that mess would be worldwide.

JohnRC

If the Earth were flung out of orbit, it would cool down very slowly -- the core of the Earth is still hot, and a few thousand kilometres of rock is a good insulation shield. There would also be quite a lot of heat generated by the Earth's remaining reserves of uranium, potassium-40, and thorium. The oceans are also a large heat reservoir; the atmosphere is not!

The first stage, I suspect, would be a substantial glaciation, in which a normal ice-age type climate would be followed by a freezing over of all the oceans, which would progress downward to the ocean floor. All plant life would die. I would expect this part of the process to take somewhere between a month or two and a decade or two, but that is just a wild guess on my part.

There would then be a significant "pause", because nothing much else would happen between T(surface average) ~ -10°C and T(surface average) ~ -150°C. Carbon dioxide would fall as hoar frost during this period, forming a layer about 1 or 2 centimetre thick; would pack down to an ice about 4 or 5 millimetre thick.

When the surface average temperature falls below ~150°C condensation from the air will start to produce liquid argon, oxygen, and nitrogen. At this stage the ground will be warmer than the air (radioactive decay energy still reaching the surface), so that the condensation will start in the atmosphere as a fine mist, and that mist will drift to the surface as the atmosphere becomes much thinner, eventually forming oceans of liquid air on top of the frozen water oceans. These oceans would contain a fairly uniform mixture of 78% nitrogen, 21% oxygen, and 1% argon, and would average roughly 30 metre deep.
The oceans would form when the temperature reached about -190°C, and would initially be rich in oxygen and argon.

The ocean would be a pale duck-egg blue colour -- if there were any light to see it with.

Only when the temperature fell below about 210°C would solid start to form at the carbon dioxide/water ice floor of the liquid air ocean -- probably starting with large crystals of argon, followed with smaller crystals of nitrogen, and eventually by tiny crystallites of a mixture of oxygen and nitrogen (separate very small crystals in a eutectic mixture). The whole effect would be ice-like with a blue surface layer.

However, there is a steady state of surface temperature that would be achieved when the energy flow from radioactive decay from the Earth's interior matched the rate of energy loss from the Earth's surface arising from blackbody-type low frequency radiation (as a radiating body at this stage, the Earth would be far from black). With a little bit of research (which I am not prepared to do) it should be possible to calculate (or at least estimate) what this temperature might be. I do not know, but I would hazard another wild guess that this would be around about -200°C, so that the oceans of liquid water might or might not form, and probably would not freeze.

chill_factor

the atmosphere can form a convective adiabat and have an upper atmospheric temperature in thermal equilibrium with space while trapping internal heat. The amount of radiated energy would be absolutely tiny because radiation scales to temperature to the 4th power and due to convection the top of the atmosphere is the only thing that's going to be in thermal equilibrium, which is at a low temperature of something like 30 degrees - and the only way to get heat off earth is through radiation. if the atmosphere is sufficiently opaque to far IR (which it is) then the absolute only way to radiate is by convecting warm air to the top of the atmosphere where it radiates; everything below the top layer is not going to radiate effectively because the far IR is going to be absorbed again.

Meanwhile there'll still be tidal stresses from the moon, internal heat and human heat.

Its very likely that a liquid ocean could survive and there'd only be massive glaciation instead of total freeze over.

Here's an article:

http://arxiv.org/abs/1102.1108

JohnRC

Here is the basis for some estimates:

Mass of atmosphere: 5.2 E 18 kg
density of liq nitrogen: 808 kg/m³ at boiling point -196°C
density of liq oxygen: 1142 kg/m³ at boiling point -183°C
estimated density of liquid air: 900 kg/m³ at boiling point
volume of liquefied atmosphere: 5.8 E 15 m³ = 5.8 E9 m.km²
surface area of earth's (water) oceans: 3.6 E 8 km²

therefore average depth of liquefied atmosphere overlying present oceanic area: 16 metre

fraction by volume of carbon dioxide 390 ppm

mass of CO2 in atmosphere 390 * 44/29 * 5.2 E 12 = 3.05 E 15 kg
total surface area of earth = 5.1 E 8 km² = 5.1 E 14 m³
density of solid CO2: 1560 kg/m³ at sublimation point –78°C
volume of solid CO2 frozen from atmosphere 2.9 E 12 m³
thickness of compact CO2 ice is therefore 0.0057 m or 5-6 mm.

----
reply to chill's post above:

Your scenario is the warmest possibility, chill. The problem with it is that the present structure of the atmosphere would not survive separation from the sun -- specifically the stratosphere which is warmed by the absorption of sunlight by ozone.

The top of the atmosphere is the thermosphere which is very very hot indeed! I presume that by "the top" you were meaning the mesopause at around 85 km altitude, which is the coldest part of the atmosphere.

If the sun were no longer in the act, then solar radiation which heats the stratosphere and the thermosphere is no longer in the action, and ozone will fairly rapidly disappear in a continuing cycle of atmospheric chemistry. There will also -- after a while -- be no cloud cover. Tidal stresses from the moon will continue to warm the Earth's from below, but they are a relatively small factor compared with continuing radioactive decay are they not?

Presumably the thermal structure of the Earth's atmosphere would revert to a simple one with decreasing temperature at increasing altitude, and you might be right that that would make radiative heat loss a very small factor; I had expected larger, with a steady state temperature around -200 °C.

Neither oxygen nor nitrogen nor argon gases can absorb infrared radiation. Once water vapour and carbon dioxide have snowed out, and methane and ozone have escaped their respective biological and photochemical replacement, and played out their chemical degradation, those are effectively the only gases left in the atmosphere -- the only reason the atmosphere is opaque to far infrared is ozone, methane, water, and carbon dioxide, as can be seen in any satellite observation through the Earth's atmosphere in the far infrared.

The Earth's low temperature darkness atmosphere would be quite transparent to far infrared.

chill_factor

yep that's true I hadn't thought of the carbon dioxide and water separating from the atmosphere.

would it be possible to pump huge amounts of methane into the atmosphere in amounts great enough to slow down the cooling?

JohnRC

I have checked up on the geothermal energy flux through the surface, and at present it amounts to about 0.1 watt per square metre. For that particular energy flux, the steady state emission temperature would probably be in the range of about 50-60 K if the emissivity of an ice-covered Earth were in the range 10-25%. The flux would increase with the geothermal gradient if the Earth's surface were to cool, but probably not by very much.

The steady state emission temperature is a firm number for a particular level of emissivity. Any remaining uncertainty and discrepancy between the picture that I have set out and that of chill_factor is down to the altitude and the "blackness" of the surface or atmospheric layer that the emission is effectively coming from.

There are two reasons, though, why pumping large amounts of methane might be unnecessary. The first is that the Earth is a huge thermal reservoir that would probably cool very slowly to reach this steady state. It should be possible to calculate how slowly; I have not yet done that. The second is that all of the plants are going to die in the darkness. They and the remaining microbiota will continue for awhile to metabolize and produce carbon dioxide, (and methane in some cases), until their environment gets too cool for them to continue. (Likewise the animals, but they are a much smaller part of the equation than plants and microbiota, which are roughly equal). This will prolong the period of high atmospheric carbon dioxide, and high level atmospheric emission from a layer much cooler than the surface.

Borek

I believe Andre (another user) posted links to papers that claimed radioactive decay plays much smaller role than it is commonly believed, and tidal heating is much more important. But I don't remember details and I can't find the thread where he posted it, so I can't check if I remember correctly.

CCWilson

Those answers are fantastic. Thanks.

Most discussions of why the Earth's core is so hot don't even mention tidal effects. They tell us that the three main causes are residual heat from the formation of the planet, frictional heat as iron and other dense materials sink, and radioactive decay.

What would happen if it did get cold enough to start raining oxygen all over the Earth? In particular, what if it rained oxygen over land that was cold enough to keep it liquid? Would it flow downhill? I'm trying to understand what the land surface would be like under those conditions. What would it be like to stand out there, warmly dressed, when oxygen and nitrogen rain starts to fall?

Drakkith

Other than it flowing downhill like any normal fluid, I'm not sure what would happen honestly. Normal rainfall comes from clouds high in the sky. I'd expect that if you were standing outside as the oxygen started to liquify if would be similar to standing outside as mist formed around you. But I really don't know.

If that's true, it would be interesting for your characters to be standing outside and wiping this liquid off of them when they suddenly realize it's the oxygen in the atmosphere condensing.

CCWilson

Once water vapor and carbon dioxide and some others rain or snow, leaving mainly oxygen and nitrogen, would there be clouds? Would there be fierce wind storms, do you think? Would all the oxygen - and later nitrogen - leave the atmosphere as rain and mist, or might it snow as well? In the first case, I suspect it would mostly collect in oceans and lakes and depressions, and only freeze when the temperature dropped even lower, leaving most land areas with just a thin layer of frozen oxygen and, later, nitrogen. If it snowed oxygen and nitrogen, there might be snow drifts and maybe deep ice over land and sea.

russ_watters

That's a rough question: That's odd because the water vapor in the air is always replenished by evaporation from the surface. We have a cycle in equilibrium. And carbon dioxide does not precipitate out. Off the top of my head, I'd say a lack of water vapor would reduce wind because water is partly a driver of the weather cycle. I could be wrong, though -- it is a pretty out-there hypothetical. No. Water precipitates because it can exist as liquid or solid at our temperature and pressure.

JohnRC

Most of the weather is driven by solar energy; with no sun, there would be much less energy to drive weather systems. However, there would still be some instability in the air column because warmer, potentially less dense air is overlain by cooler, and so convection cells may well be set up.

Apart from local factors like volcanic eruptions, I think that the air circulation might be a fairly gentle trade wind type pattern, driven by geothermal warming at the surface, and by tidal effects on both land and air mass. With solid oceans there would be no oceanic circulation to interact with the atmospheric system.

When the surface temperature gets to about -150°C (and the upper atmosphere is somewhat cooler), condensation to liquid argon and liquid oxygen can begin in the upper atmosphere. This will actually have a local warming effect (release of latent heat), and any downward motion of liquid droplets will also have a (smaller?) warming effect (dissipation of gravitational kinetic energy).

So the actual cooling is likely to stall between -150° and -200° C surface temperature.
While the cooling only proceeds slowly, oceans of oxygen will start to form -- more likely from gently descending mists rather than actual rainfall. At this stage oxygen snow is unlikely, because oxygen has a good wide liquid range. Towards the end of this stage, though nitrogen will probably form as crystallites of snow or hoar frost as well as mist. And the other factor is that the atmosphere will become very thin.

At about -210°C = 63 K the oceans -- uniform depth of about 14 metre over the oceanic 71% of Earth's surface -- will start to freeze. The atmosphere at this stage will have a pressure of roughly 4 Pa, made up of about 60% neon, 25% nitrogen and falling, 13% helium and very slowly rising, and 1% hydrogen (this does not allow for any meteoric material that might have been picked up during Earth's escape from the solar system

Borek

Once we get to temperatures where nitrogen and oxygen are liquid, water and carbon dioxide become rock solid (pun intended). They will be still able to sublime, but I am not convinced their partial pressures will be high enough to be of any meteorological importance.