3 ms·

It always fascinates me the inner core of our planet, after all it is from what we know a swilling mass of hot melting metal and other elements. Which is ever

by Zenst 3y ago

It always fascinates me the inner core of our planet, after all it is from what we know a swilling mass of hot melting metal and other elements. Which is ever so slowly cooling at a size and scale we find hard to imagine. Are their events that bring about rapid cooling, or are there mechanisms that maintain or induce the heating, scale of planet and subsequent pressure, or perhaps even cosmic rays impact it are thoughts, but the deeper we look, the more questions we find and still a case of solve less answers than questions and yet to reach that point in which we fully understand it. Perhaps and very probably, Mars was a thriving ecosystem whilst the earth was still a molten blob of rock. Just the scale of time in the universe well outpaces biological life when talking billions of years.

BurningFrog 3y ago
The major force keeping our core hot is nuclear fission. https://blogs.scientificamerican.com/observations/nuclear-fission-confirmed-as-source-of-more-than-half-of-earths-heat/ https://blogs.scientificamerican.com/observations/nuclear-fi...
- JackMcMack 3y ago
  Interesting read. Though it says the nuclear fission happens in the crust and mantle, not the core.
  - idlewords 3y ago
    Here's a survey paper with a deeper treatment of the topic, for Earth and other solar system bodies: https://link.springer.com/article/10.1007/s11214-020-00656-z https://link.springer.com/article/10.1007/s11214-020-00656-z "On the Distribution and Variation of Radioactive Heat Producing Elements Within Meteorites, the Earth, and Planets"
- rvilim 3y ago
  You've got to be careful here. This article refers to the heat budget of the _entire_ earth, not the Earth's core. The Earth's core has relatively little in the way of radiogenic elements now. Most of the heat originating in the core comes from - The formation of the earth (called primordial heat) - Latent heat (released when iron freezes onto the solid core) - Differentiation (e.g. settling of heavy stuff to the bottom) The mantle is chock full of radiogenic elements though.
  - yongjik 3y ago
    Well, yes, but it basically means the core is wrapped in a heat-producing blanket (the rest of the Earth), so we can say that the fissile materials on the outer parts of the Earth does keep the core stay warm.
    - BurningFrog 3y ago
      That's what my physics instincts tell me. It might take centuries for heat to conduct across the planet interior, but it has nowhere else to go. I'm open to being told my instructions are wrong in this case though.
    - rvilim 3y ago
      I wouldn't say that the best way of thinking about it is the blanket analogy because conduction is _not_ the primary way that the earth sheds heat, convection in the mantle is. Though I haven't run the numbers, I would strongly bet that the core would be _hotter_ than it is right now if the mantle did not have internal heating. The reason being that, the rate at which you remove heat from the core (e.g. the rate at which the core cools) is entirely determined by the rate at which mantle convection removes heat. Radiogenic heat is a _strong_ driver of mantle convection in the earth, without radiogenic isotopes you would get much more sluggish mantle convection and a much lower rate of heat removal from the core. The reason for this is twofold: - Internal heating leads to higher temperatures which leads to lower viscosity and more vigorous mantle convection - Internal heating will locally heat cold "blobs" and make the buoyant I would also (much less strongly) bet that plate tectonics would not occur without internal heating. We only see plate tectonics in a narrow slice or parameter space in mantle convection models and once you get plate tectonics you get _much_ more heat removal and _much_ faster cooling.
- perihelions 3y ago
  Err, that SciAm author misunderstood that research... what they wrote is exactly backwards. The neutrino observations they're talking about disproved the natural nuclear reactor hypothesis. There is no antineutrino signal from the Earth of the type a nuclear fission process would emit. https://arxiv.org/abs/1909.02257 https://arxiv.org/abs/1909.02257 ("Comprehensive geoneutrino analysis with Borexino") What Borexino found was about 25 terawatts of radioactive decay occurring inside the Earth—alpha decay of 238U and 232Th. But, no nuclear fission. If there are fissioning critical masses inside the Earth, the total amount, constrained by neutrino counts, is no more than 2.4 terawatts (and consistent with 0).
pkaye 3y ago
From what I understand Mars is smaller mass than earth so it cooled faster. I can imagine other factor like lower gravity that makes it easier for the atmosphere and water to easily escape to space.
Modified3019 3y ago
If you’re looking for curious concepts, with no real way to test and verify, you could consider that because of the whole heliosphere thing our solar system has going on, there are higher and lower areas of current flowing through space, and planets could potentially act like a resistor in some circumstances, which could be gained or lost. Thus far though, science seems mostly satisfied with radioactive decay Edit: https://news.ycombinator.com/item?id=38061230 https://news.ycombinator.com/item?id=38061230 and the things rvilim mentions

by Zenst 3y ago

BurningFrog 3y ago

The major force keeping our core hot is nuclear fission. https://blogs.scientificamerican.com/observations/nuclear-fission-confirmed-as-source-of-more-than-half-of-earths-heat/ https://blogs.scientificamerican.com/observations/nuclear-fi...

JackMcMack 3y ago
Interesting read. Though it says the nuclear fission happens in the crust and mantle, not the core.
- idlewords 3y ago
  Here's a survey paper with a deeper treatment of the topic, for Earth and other solar system bodies: https://link.springer.com/article/10.1007/s11214-020-00656-z https://link.springer.com/article/10.1007/s11214-020-00656-z "On the Distribution and Variation of Radioactive Heat Producing Elements Within Meteorites, the Earth, and Planets"
rvilim 3y ago
You've got to be careful here. This article refers to the heat budget of the _entire_ earth, not the Earth's core. The Earth's core has relatively little in the way of radiogenic elements now. Most of the heat originating in the core comes from - The formation of the earth (called primordial heat) - Latent heat (released when iron freezes onto the solid core) - Differentiation (e.g. settling of heavy stuff to the bottom) The mantle is chock full of radiogenic elements though.
- yongjik 3y ago
  Well, yes, but it basically means the core is wrapped in a heat-producing blanket (the rest of the Earth), so we can say that the fissile materials on the outer parts of the Earth does keep the core stay warm.
  - BurningFrog 3y ago
    That's what my physics instincts tell me. It might take centuries for heat to conduct across the planet interior, but it has nowhere else to go. I'm open to being told my instructions are wrong in this case though.
  - rvilim 3y ago
    I wouldn't say that the best way of thinking about it is the blanket analogy because conduction is _not_ the primary way that the earth sheds heat, convection in the mantle is. Though I haven't run the numbers, I would strongly bet that the core would be _hotter_ than it is right now if the mantle did not have internal heating. The reason being that, the rate at which you remove heat from the core (e.g. the rate at which the core cools) is entirely determined by the rate at which mantle convection removes heat. Radiogenic heat is a _strong_ driver of mantle convection in the earth, without radiogenic isotopes you would get much more sluggish mantle convection and a much lower rate of heat removal from the core. The reason for this is twofold: - Internal heating leads to higher temperatures which leads to lower viscosity and more vigorous mantle convection - Internal heating will locally heat cold "blobs" and make the buoyant I would also (much less strongly) bet that plate tectonics would not occur without internal heating. We only see plate tectonics in a narrow slice or parameter space in mantle convection models and once you get plate tectonics you get _much_ more heat removal and _much_ faster cooling.
perihelions 3y ago
Err, that SciAm author misunderstood that research... what they wrote is exactly backwards. The neutrino observations they're talking about disproved the natural nuclear reactor hypothesis. There is no antineutrino signal from the Earth of the type a nuclear fission process would emit. https://arxiv.org/abs/1909.02257 https://arxiv.org/abs/1909.02257 ("Comprehensive geoneutrino analysis with Borexino") What Borexino found was about 25 terawatts of radioactive decay occurring inside the Earth—alpha decay of 238U and 232Th. But, no nuclear fission. If there are fissioning critical masses inside the Earth, the total amount, constrained by neutrino counts, is no more than 2.4 terawatts (and consistent with 0).

pkaye 3y ago

From what I understand Mars is smaller mass than earth so it cooled faster. I can imagine other factor like lower gravity that makes it easier for the atmosphere and water to easily escape to space.

Modified3019 3y ago

If you’re looking for curious concepts, with no real way to test and verify, you could consider that because of the whole heliosphere thing our solar system has going on, there are higher and lower areas of current flowing through space, and planets could potentially act like a resistor in some circumstances, which could be gained or lost. Thus far though, science seems mostly satisfied with radioactive decay Edit: https://news.ycombinator.com/item?id=38061230 https://news.ycombinator.com/item?id=38061230 and the things rvilim mentions