The dying of the light

[eatU4myT]

Let's suppose for a moment that our descendants in 1 billion years have forgotten that the sun was expected to become a red giant. Perhaps they lost all the astronomy text books in a freak yachting accident, who knows. At any rate, they have access to all of the scientific instruments that we have sent into/pointed at space, and also to the results that we have obtained by using those instruments in our time. Which instruments and observations would be the first to suggest to them that something was happening to the sun?

[DDE]

1 hour ago, eatU4myT said:

Which instruments and observations would be the first to suggest to them that something was happening to the sun?

Here's the problem: there is no single point where something starts to happen to the Sun. The initial process that has a fatal outcome for the Earth's biosphere - the increase in luminosity - occurs gradually over a geological time scale:

So they should be able to always observe such a tendency... if, and only if, they crunch numbers over hundreds of millions of years to get a statistically significant trend.

[Shpaget]

Dude 1: Hey Dude 2, look what I found! An ancient image, I think they called it photograph, of the setting Sun as viewed from this exact location. Look how tiny the Sun was back then.

Dude 2: Awesome! Wait what?

[kerbiloid]

Bacteria 1: Bloop!

Bacteria 2: Gurple!

Conditions are rather different to let the yellow-dwarf life keep existing on the same planet under the red giant.
And as the geological processes have stopped, no new life can appear, only the existing one is getting extinct without the magnetosphere.

Edited August 16, 2020 by kerbiloid

[Guest]

Existing one can adapt to live without magnetosphere, though. As long as it happens gradually enough, additional protections against radiation will develop. Some organisms already have them, Tardigrades can survive inside a nuclear reactor, for example. In fact, in Chernobyl there is a mold that feeds on radiation. Life isn't just big animals and humans. Indeed, all those are quite heavily optimized for a very specific environment, and it doesn't take much to kill them off. It likely won't ever go down to bacteria, it might regress to insects for a while. And of course, marine life won't be affected by losing the magnetosphere, because it's living inside a pretty solid radiation shield. As long as the oceans don't boil off, anyway.

Also, geological processes have not stopped. Ask anyone living in Japan, California or a Yellowstone park ranger. Completely new forms of life don't appear, but that's only because existing ones are hogging all ecological niches already.

1 hour ago, DDE said:

Here's the problem: there is no single point where something starts to happen to the Sun. The initial process that has a fatal outcome for the Earth's biosphere - the increase in luminosity - occurs gradually over a geological time scale:

It won't be fatal to Earth's biosphere for a long, long time, though. Sun will increase in luminosity on geological timescales, far longer than those evolution works at. So, Earth's biosphere will adapt, gradually, to ever increasing temperatures, as it has already been doing. 

Unless humans get involved, the organisms living on Earth a billion years from now will resemble modern ones about as much as moderns biosphere resembles the one from a billion years ago. That is to say, very little. There will be some kind of life on Earth as long as it's physically possible for it to be. Indeed, from what we know so far, the only threat to life in general are changes that occur faster than evolution can keep up (this is what happens during a mass extinction event). Even when the Earth ends up inside the Sun, for all we know, we might just end up with creatures adapted to survive and thrive inside a star. There might be some thermodynamic barriers to it going quite that far, since most molecules fall apart at that temperature, but seeing as organisms had managed to adapt and even compete with each other in areas that regularly go below zero, which normally destroys cells by causing the water in them to freeze, I'd say it's got a pretty good chance. 

Edited August 16, 2020 by Guest

[K^2]

4 minutes ago, Dragon01 said:

Even when the Earth ends up inside the Sun, for all we know, we might just end up with creatures adapted to survive and thrive inside a star.

I was with you up to this point, but here I have to call B.S. Even if hypothetically life can exist in a star, which seems very dubious from thermodynamic perspective, it can't be life that evolves from anything on Earth. First of all, because absolutely everything life here uses in one way or another relies on chemical bonds, which go away completely in Sun's atmosphere. Secondly, because while it starts out slowly, once the star expands sufficiently, the descent from, "Oh, it's really hot in here," to "Planet's becoming part of the star and chemical bonds are failing," is actually pretty rapid. So you are asking for an impossible adaptation to happen in impossibly short time, and this is not a case where two negatives cancel each other out.

Now, if, say, Mars becomes habitable again due to temperature increase, some rock from Earth can end up there, (re?)seeding life. So Earth life can, indeed, survive demise of the planet itself even without Humanity's or any other civilization's help, but it would be via planet-hopping, not living inside a star.

[eatU4myT]

1 hour ago, DDE said:

[helpful graph]

That's interesting, I guess I'd always imagined it being less of a straight-line-ish sort of thing, even over the timescales involved.

Ok, lets phrase it another way perhaps.  Assuming that all the measurements are available over the millions of years as above, but no-one has bothered to crunch the numbers (Dude 1's ancestors were in charge, and preoccupied with taking pretty photos of sunsets).  Which sets of data is Dude 2 going to run back to the lab to start crunching?  What instruments are we currently using to monitor the sun's luminosity, and the characteristics of Earth's magnetosphere?  What other physical characteristics of the Sun/Earth would he be looking into?

[Guest]

25 minutes ago, K^2 said:

I was with you up to this point, but here I have to call B.S. Even if hypothetically life can exist in a star, which seems very dubious from thermodynamic perspective, it can't be life that evolves from anything on Earth. First of all, because absolutely everything life here uses in one way or another relies on chemical bonds, which go away completely in Sun's atmosphere. Secondly, because while it starts out slowly, once the star expands sufficiently, the descent from, "Oh, it's really hot in here," to "Planet's becoming part of the star and chemical bonds are failing," is actually pretty rapid. So you are asking for an impossible adaptation to happen in impossibly short time, and this is not a case where two negatives cancel each other out.

That's what the second line about "some thermodynamic barriers" addressed. However, do not dismiss that idea so quickly. In particular, you'd be surprised what can survive inside a rock. What I've been thinking of is life evolving on the surface, in the increasing heat, and colonizing deep regions of Earth. There are already bacteria found very deep underground, and as the surface temperatures increase, I would expect the biosphere, now adapted to higher temperatures, would penetrate even deeper. Now, heat transfer through a rock is pretty slow, and while the transition might not be slow on the surface, it certainly will be so a few kilometers underground. Life may not be able to survive on Earth by the time it ends up inside the Sun, it might well be able to last in it.

I've seen enough extremophiles to treat any "it can't be life that evolves from anything on Earth" type statements with suspicion. Some of these organisms are really puzzling, and quite a few of them turned out not to be relics of the very first organisms, but modern organisms that took up the niche (and probably outcompeted any then-living fossils that lived there). Seriously, what chances would you give that Chernobyl mold evolving from anything we know? It took life one billion years to go from plankton to humans and everything else. It'll be several times more than that before Earth even gets near the Sun. 

Edited August 16, 2020 by Guest

[K^2]

@Dragon01 How is that supposed to work, when atoms don't form molecules anymore?

[eatU4myT]

Hey folks, I don't post much in this sub-forum so I don't know how the rules are usually applied, but could I respectfully ask for this thread to stay on-topic to answering the question posed?  Apologies if there is an answer to the question posed in the discussion being had, I may be have missed it - if so, some explanation to link it to the question would be appreciated to help me learn.

Thanks

[kerbiloid]

It's absolutely obvious that no kind of biological life can survive the geological death of a planet.

It's very simple.

The geological processes stop when internal sources of energy stop producing enough heat to keep the core liquid.

The core stops being liquid → the flows of melted iron stop flowing → the electric currents caused by the molten iron flows stop being generated → the dynamo stops → the magnetosphere disappears → the solar wind stops getting stopped by the magnetosphere → the solar wind starts bombarding the upper layers of the dense atmosphere → the ozone layer gets burnt → the solar UV freely irradiates the water clouds and the ocean surface → the water starts intensively being splitted into oxygen and the hydrogen → the oxygen starts burning everything, while the hydrogen easily escapes and leaves the atmosphere → both oxygen amd nitrogen (molecular mass ~30) escape the atmosphere → the atmosphere gets more and more carbon-oxide, and the greenhouse effect grows exponentially making all these processes running faster → the planet turns into a hot Venus or a frozen Venus with no traces of life neither in air, nor on surface, nor in surface cracks and caves → a totally lifeless piece of stone with carbon-dioxide atmosphere is floating in time and space in the rays of the expanding Sun making it hotter and hotter, until the gas drag makes the planet stick into the star and be destroyed.

Poor, poor Earth! Its geological history will end almost simultaneously with the Sun becoming a red giant in 1.5-2 billion years, and nobody will see its final days!

[mikegarrison]

47 minutes ago, eatU4myT said:

Hey folks, I don't post much in this sub-forum so I don't know how the rules are usually applied, but could I respectfully ask for this thread to stay on-topic to answering the question posed?  Apologies if there is an answer to the question posed in the discussion being had, I may be have missed it - if so, some explanation to link it to the question would be appreciated to help me learn.

Thanks

Really? The very first words of the first response answered your question.

3 hours ago, DDE said:

Here's the problem: there is no single point where something starts to happen to the Sun.

 

[eatU4myT]

12 minutes ago, mikegarrison said:

Really? The very first words of the first response answered your question.

3 hours ago, DDE said:

Here's the problem: there is no single point where something starts to happen to the Sun.

 

Yes, which was a very helpful response - thanks to Shpaget and especially DDE for their posts.  I've re-phrased the question a little though, a few posts later, as I didn't do a good job of posing it originally.

Edited August 16, 2020 by eatU4myT

[DDE]

2 hours ago, eatU4myT said:

That's interesting, I guess I'd always imagined it being less of a straight-line-ish sort of thing, even over the timescales involved.

Ok, lets phrase it another way perhaps.  Assuming that all the measurements are available over the millions of years as above, but no-one has bothered to crunch the numbers (Dude 1's ancestors were in charge, and preoccupied with taking pretty photos of sunsets).  Which sets of data is Dude 2 going to run back to the lab to start crunching?  What instruments are we currently using to monitor the sun's luminosity, and the characteristics of Earth's magnetosphere?  What other physical characteristics of the Sun/Earth would he be looking into?

Let's ignore the funky thing that is the magnetosphere. The actual brightness of sunlight is continuously monitored using pyrheliometers (narrow-angle, targeted sensor) and pyranometers (has a sort of fisheye lens). There seems to be a vast international effort to keep those devices well-calibrated relative to each other, so something as mundane as the sun getting brighter beyond the normal cycles will be, sooner or later, measurable.

Of course, this would have to be confirmed by other means. Measurement of the Sun's size is primarily a focus of helioseismology, but on the timescales offered, trying to verify the measurements bored Greeks performed with rudimentary trigonometry and a few imaginary observers in wells in different cities (IIRC) can uncover discrepancies.

I think studying the history of how Mercury's orbit does not comply with Newtonian physics, and proved a mystery until publications by a cheeky Austrian oatent clerk, could prove illustrative.

[kerbiloid]

Let me suggest several indicators.

1. Ice melting. Here and anywhere in the Solar system. Ice melts → albedo falls, something visible gets invisible. Say, no visible Jovian moons.

2. Brightness growing. Albedo of celestial bodies stays same, but the Sun luminosity grows, so the brightness of the reflecting things grows, too, and some of them become visible from here.
Say, Neptune gets so bright that postmagnetospheric-we can see it with bare eyes.

3. Comets. Either they got so bright and the sky is full of them , or they got evaporated, and there are no visible comets.

These events look more discrete than the smooth graphic line. Either you see five planets or six.

Edited August 16, 2020 by kerbiloid

[Guest]

3 hours ago, K^2 said:

@Dragon01 How is that supposed to work, when atoms don't form molecules anymore?

Because Earth is a great big hunk of rock and unless we stripmine it all in the meantime, it'll still be a great big hunk of rock. Hunks of rock that big take some time to heat up and fall apart, even in the solar corona, which, despite impressive temperature readings, isn't very dense. I'm not saying that it'll last forever. I'm saying that it might have a brief heyday before the planet falls apart. Life can be ridiculously robust.

Unless we're talking about hitting the photosphere, of course, not the corona, like I assumed. But then, tidal forces and thermal stresses would likely have long since broke the Earth up, and if not, the photosphere is dense enough that an object travelling as fast as the Earth would almost certainly break up on impact, making the point moot.

2 hours ago, kerbiloid said:

the planet turns into a hot Venus or a frozen Venus with no traces of life neither in air, nor on surface, nor in surface cracks and caves

Tardigrades (and a bunch of other extremophiles you haven't heard of) would like a word with you. You severely underestimate the ability of life to adapt to extreme conditions. Magnetosphere is only necessary for life as we know it. It will not go away quickly enough to prevent adaptation. Life will find a way, nuclear reactors can get clogged with bacterial films, there are microbes that can live in total vacuum, and several very much macroscopic organisms can handle extreme cold. That's what exists on life-friendly Earth, with not much pressure towards evolving extermophiles. If those conditions onset gradually, it's a safe bet that something out of our very varied biosphere will survive to adapt.

This is also why it's so important that we decontaminate out probes very thoroughly. Mars has no magnetosphere and a pretty nasty climate, but there is a number of Earth organisms that would love it down there. Particularly because they would have no others to compete with. 

[kerbiloid]

7 minutes ago, Dragon01 said:

Tardigrades (and a bunch of other extremophiles you haven't heard of) would like a word with you.

Tardigrades would just die a little slower and in their sleep. They are not terminators.

8 minutes ago, Dragon01 said:

You severely underestimate the ability of life to adapt to extreme conditions.

Still no known species can survive in Venusian conditions.

9 minutes ago, Dragon01 said:

Magnetosphere is only necessary for life as we know it.

Without the magnetosphere there is no hydrosphere. So, no hot springs to survive in.

11 minutes ago, Dragon01 said:

Life will find a way, nuclear reactors can get clogged with bacterial films

No known reactor is populated for more that several years, and there are still water and oxygen inside.

[Guest]

Just now, kerbiloid said:

Without the magnetosphere there is no hydrosphere. So, no hot springs to survive in.

There is clear evidence of liquid water on Mars, and that means it has a hydrosphere, however small, despite the lack of magnetosphere. It's not in neat pools on the surface, but it's not a big problem. The new rover is expected to tell us more about it. Lack of magnetosphere does not preclude liquid water.

Quote

Still no known species can survive in Venusian conditions.

No known species ever had to. Venus never had life in first place, and there are no places on Earth that would have similar conditions. Here, it's easier to find cold places than very hot ones. There are hydrothermal vents, but they are surrounded by very cold water, so it's a bad example, and they don't get that hot in first place, anyway. 

[kerbiloid]

50 minutes ago, Dragon01 said:

There is clear evidence of liquid water on Mars

Several billion years ago.
Mars is farther from the Sun, it gets dry slower, and there is no known traces of life on it.
When it gets a little warmer, all traces of the atmo- an hydrosphere will escape away quickly and finally.

It's just a dry stone covered with frost.

50 minutes ago, Dragon01 said:

there are no places on Earth that would have similar conditions.

Because the Earth haven't face the irreversible greenhouse effect and never was as dry and hot.
When it becomes, the life will have same chances to survive like on Venus.

Hydrothermal vents exist only because the pressure of the water vapor in atmosphere lets it stay liquid rather than evaporate.

Also they are just +200+°C, not +480°C, and not under 90 atm pressure of CO2.

(That's another factor. In hot CO2 atmosphere any water will turn into acid and dissolve the life)

Edited August 16, 2020 by kerbiloid

[magnemoe]

8 hours ago, eatU4myT said:

Let's suppose for a moment that our descendants in 1 billion years have forgotten that the sun was expected to become a red giant. Perhaps they lost all the astronomy text books in a freak yachting accident, who knows. At any rate, they have access to all of the scientific instruments that we have sent into/pointed at space, and also to the results that we have obtained by using those instruments in our time. Which instruments and observations would be the first to suggest to them that something was happening to the sun?

Probably by studying the stars and discover the standard diagram for stars, and then find that they get brighter over time. 
As other say its not something who is noticeable within even civilization lifespans. 

Most likely the biosphere would adjust well enough as its so long term but its limits. 
That to do about it well many of the geoenginering ideas we talk about combating global warming will work just as well here. 
One problem with an hotter sun is that if you get an very hot planet for other reasons like  during the Carboniferous with mush higher solar input this could go wrong. 


 

[magnemoe]

2 minutes ago, kerbiloid said:

Several billion years ago.
Mars is farther from the Sun, it gets dry slower, and there is no known traces of life on it.
When it gets a little warmer, all traces of the atmo- an hydrosphere will escape away quickly and finally.

It's just a dry stone covered with frost.

Because the Earth haven't face the irreversible greenhouse effect and never was as dry and hot.
When it becomes, the life will have same chances to survive like on Venus.

Hydrothermal vents exist only because the pressure of the water vapor in atmosphere lets it stay liquid rather than evaporate.

Also they are just +200+°C, not +480°C, and not under 90 atm pressure of CO2.

(That's another factor. In CO2 atmosphere any water will turn into acid and dissolve the life)

Mars is likely to small so it cooled too fast and lost its magnetic field. It also has low gravity making it easy for the atmosphere to escape from in the first place. 
Make mars larger an give it an large moon to help tidal forces keep the core alive. 

Good chance Venus never had an good magnetosphere as it rotate so slowly. It also lack plate tectonic. Rater it get some gigantic volcano eruptions around every 200 million years.
Think 20 Siberian traps at once. So stuff was stacked against it. Lots of stuff went wrong there. 

Now one weird theoretical exoplanet is an Venus like planet with lots of oxygen in the atmosphere. 
Say Venus formed as an true water world with say 50 km deep oceans. Planet first become an steam planet, then the water vapor split into hydrogen and oxygen, its not enough carbon around for the oxygen to bind to. Less volcanism help here. 
You end with an Venus like atmosphere but with lots of oxygen in it. 

[kerbiloid]

2 minutes ago, magnemoe said:

Mars is likely to small so it cooled too fast and lost its magnetic field. It also has low gravity making it easy for the atmosphere to escape from in the first place. 
Make mars larger an give it an large moon to help tidal forces keep the core alive. 

If it was bigger, it would be covered with thick ice, because even Earth was.
So, still no liquid water and just awaiting for its loss in future: slowly from UV, quickly from the Sun luminosity growth.

4 minutes ago, magnemoe said:

Good chance Venus never had an good magnetosphere as it rotate so slowly. It also lack plate tectonic. Rater it get some gigantic volcano eruptions around every 200 million years.
Think 20 Siberian traps at once. So stuff was stacked against it. Lots of stuff went wrong there. 

Yes, a final fireworks.
But how does this relate to its water? Did it have liquid water in the past? Did it have life?

5 minutes ago, magnemoe said:

Say Venus formed as an true water world with say 50 km deep oceans.

Unlikely, as the ocean volume per planet mass depends on the water ice concentration in the protoplanetary dust, but ok.

6 minutes ago, magnemoe said:

Planet first become an steam planet, then the water vapor split into hydrogen and oxygen, its not enough carbon around for the oxygen to bind to.

The water vapor is a greenhouse gas itself. It will irreversibly heat up and become an atmosphereless Venus.
The oxygen escapes like it did from the real Venus.

[Vanamonde]

They would figure it out the same way we did: by observing other stars and recognizing that they are snapshots in a process, and it's a process which our sun will follow just like older stars of the same mass. They wouldn't need to directly witness changes to realize what's happening. 

[Guest]

1 hour ago, kerbiloid said:

Several billion years ago.

Right now:
https://en.wikipedia.org/wiki/Seasonal_flows_on_warm_Martian_slopes

This is not some old rock patterns, we're talking about good evidence of water flowing around Mars on seasonal basis. It's literally happening right now. If you followed Curiosity, you'd know that it was, in fact, redirected to avoid getting near one such flow, for fear it could contaminate it. Mars is a perfectly good place for some hardy microbes to live, and we don't want to get Earth ones a chance.

1 hour ago, kerbiloid said:

and not under 90 atm pressure of CO2.

(That's another factor. In hot CO2 atmosphere any water will turn into acid and dissolve the life)

Actually, the pressure at the bottom of Mariana Trench is 1000atm. Things live there. Venus has nothing on the bottom of the ocean in that regard. Pressure doesn't really matter, as long as it's consistent, it can be whatever. As for acid, there are archea living in far worse conditions than a CO2-heavy atmosphere. Indeed, with enough sunlight, atmosphere rich in CO2 is quite great for photosynthesizing organisms. Also, high CO2 pressure would make it easier to absorb. There's a reason Venus was often portrayed as ravenous, tropical jungle in early SF. If it wasn't for the heat, it'd be a perfect place for plantlife.

The primary showstopper on Venus is temperature, and we have no good counterpart to that because no environment on Earth is that hot (active volcanoes are much hotter). So far we don't know of any organism capable of withstanding that. That doesn't mean it's impossible, or that we won't at some point find some crazy thing that likes to live next to a lava flow. 

[wumpus]

58 minutes ago, Dragon01 said:

The primary showstopper on Venus is temperature, and we have no good counterpart to that because no environment on Earth is that hot (active volcanoes are much hotter). So far we don't know of any organism capable of withstanding that. That doesn't mean it's impossible, or that we won't at some point find some crazy thing that likes to live next to a lava flow. 

Life exists near undersea hydrothermal vents (the only ecosystem that doesn't require sunlight), but only up to ~130C.  Venus is more like ~470C, something no Earth based life seems possible of being able to handle (although I wouldn't have expected >100C either).