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DaCaptain
2018-May-23, 08:40 PM
I've often wondered, is the earth really just a failed star?

Hornblower
2018-May-23, 08:43 PM
I've often wondered, is the earth really just a failed star?

No.

SagittariusAStar
2018-May-23, 08:55 PM
No, it's a successful planet.

antoniseb
2018-May-23, 10:38 PM
I'd like to point out that the phrase "failed star" is not a technical term with a specific meaning. I recall Arthur C Clarke using it to describe Jupiter in one of his works of fiction, but even Jupiter is a stretch to call a failed star.
I take the term, these days, to refer to some object that formed as one of several starless cores in a protostellar cloud, and one or more of the other cores became stars first, and blew away enough material around this core that never became even a red dwarf. (Exo)planets form after the core the orbit becomes a star using a different process. It is possible that some environments will result in sequences of events where some objects will be in a gray area between the two, but at the moment, there is no need for being able to precisely identify every case, so the terminology remains fuzzy.

Copernicus
2018-May-24, 01:09 AM
Future star material.

DaCaptain
2018-May-24, 02:47 AM
I've often wondered, is the earth really just a failed star?

My reasoning for this question is that the core doesn't seem to be cooling down. There's got to be a fusion reaction going on in the center that's been keeping it going for so long. It's not as hot as the sun so that's why I was thinking, failed star. Doesn't seem like geomagnetic forces alone could account for all the heat that's been generated during it's lifetime. Without a reaction I'd think that after a while everything would have become tidally locked and cooled down, like Mars, a long time ago.

Jens
2018-May-24, 04:12 AM
My reasoning for this question is that the core doesn't seem to be cooling down. There's got to be a fusion reaction going on in the center that's been keeping it going for so long. It's not as hot as the sun so that's why I was thinking, failed star. Doesn't seem like geomagnetic forces alone could account for all the heat that's been generated during it's lifetime. Without a reaction I'd think that after a while everything would have become tidally locked and cooled down, like Mars, a long time ago.

I think there have been suggestions that fusion takes place in the earth's core, but there is not a consensus that it does or doesn't.

Shaula
2018-May-24, 04:25 AM
I think there have been suggestions that fusion takes place in the earth's core, but there is not a consensus that it does or doesn't.
The only suggestions for any significant level of fusion in the core I've seen come from cold fusion advocates and are not backed by credible evidence.


My reasoning for this question is that the core doesn't seem to be cooling down. There's got to be a fusion reaction going on in the center that's been keeping it going for so long. It's not as hot as the sun so that's why I was thinking, failed star. Doesn't seem like geomagnetic forces alone could account for all the heat that's been generated during it's lifetime. Without a reaction I'd think that after a while everything would have become tidally locked and cooled down, like Mars, a long time ago.
You might want to run some numbers (or read some papers on models which do) for that. Currently models suggest that the core is cooling, just slowly. The energy budget, once you include radioactive decay, latent heats of crystallisation and frictional heating, shows a small deficit from equilibrium conditions. The collision with the object that led to the Moon's formation helped stir things up by injecting a large pulse of heat. Mars is a poor comparison because it is much smaller and didn't have a Theia event. These factors lead to the lower core temperature estimate of 1500K for Mars (but it may be partly liquid). It also isn't tidally locked.

Ken G
2018-May-24, 06:48 AM
My reasoning for this question is that the core doesn't seem to be cooling down. There's got to be a fusion reaction going on in the center that's been keeping it going for so long.If you replace "fusion" with "fission," then your thinking is correct. Note that fusion releases heat from building larger nuclei from smaller ones (like hydrogen into helium in stars), whereas fission releases heat by breaking up very large nuclei (like uranium and plutonium). There isn't hydrogen and helium in Earth's core, and the temperature is not high enough anyway, so it's not so much failing at fusion as it is succeeding at fission.

profloater
2018-May-24, 01:27 PM
I recall the great Kelvin calculated that the Earth should have cooled down but he did not know about fission, so the fission contribution might be significant. But then were the solar balances and the current idea of the history well understood by Kelvin?

George
2018-May-24, 01:43 PM
I recall the great Kelvin calculated that the Earth should have cooled down but he did not know about fission, so the fission contribution might be significant. Yes, he used his knowledge of heat transfer and thermodynamics to calculate the time needed to cool the Earth from an assumed molten state, as was deemed likely upon formation. He had temperature gradient data taken in mines and calculated, initially IIRC, a 20 million year age. He later received deeper mine temp. data, I think, and came up with 100 million years. Darwin called him an "odious specter" since that was too young an age for his evolutionary theory.

Along came Rutherford with his new knowledge of radioactive decay and in a dramatic meeting, which Kelvin attended, the somewhat apprehensive Rutherford pointed out Lord Kelvin's error, but he carefully crafted his words. :)



But then were the solar balances and the current idea of the history well understood by Kelvin? Yes, no doubt, since even IR (from Herschel's discovery) was known in 1800, decades before Kelvin's work.

It's worth mentioning, per what I've learned from Ken's posts in the past, that internal convection plays an important role as well.

grapes
2018-May-24, 03:30 PM
You might want to run some numbers (or read some papers on models which do) for that. Currently models suggest that the core is cooling, just slowly. The energy budget, once you include radioactive decay, latent heats of crystallisation and frictional heating, shows a small deficit from equilibrium conditions. The collision with the object that led to the Moon's formation helped stir things up by injecting a large pulse of heat. Mars is a poor comparison because it is much smaller and didn't have a Theia event. These factors lead to the lower core temperature estimate of 1500K for Mars (but it may be partly liquid). It also isn't tidally locked.
Last time I looked, it seemed the greatest effect on the model was that the radioactive decay was concentrated near the surface, biasing those heat loss calculations. Left over heat of formation was the largest part of the budget in the core.

DaCaptain
2018-May-24, 03:31 PM
If you replace "fusion" with "fission," then your thinking is correct. ....

That was kind of my thinking in the first place. It failed to get the materials it needed for fusion.

profloater
2018-May-24, 04:01 PM
Yes, he used his knowledge of heat transfer and thermodynamics to calculate the time needed to cool the Earth from an assumed molten state, as was deemed likely upon formation. He had temperature gradient data taken in mines and calculated, initially IIRC, a 20 million year age. He later received deeper mine temp. data, I think, and came up with 100 million years. Darwin called him an "odious specter" since that was too young an age for his evolutionary theory.

Along came Rutherford with his new knowledge of radioactive decay and in a dramatic meeting, which Kelvin attended, the somewhat apprehensive Rutherford pointed out Lord Kelvin's error, but he carefully crafted his words. :)


Yes, no doubt, since even IR (from Herschel's discovery) was known in 1800, decades before Kelvin's work.

It's worth mentioning, per what I've learned from Ken's posts in the past, that internal convection plays an important role as well.

thanks for that, fills in the details.:)

grapes
2018-May-24, 04:20 PM
That was kind of my thinking in the first place. It failed to get the materials it needed for fusion.
That's taking it a little too far--we're all failed stars then :)

ETA: usually, "failed star" implies getting close to being, not just a complete miss.

George
2018-May-24, 04:39 PM
Last time I looked, it seemed the greatest effect on the model was that the radioactive decay was concentrated near the surface, biasing those heat loss calculations. Left over heat of formation was the largest part of the budget in the core. Why would this be the case? Uranium is heavy. Or is it because the outer 2km comprises a volume for its shell > the core volume?

George
2018-May-24, 04:44 PM
thanks for that, fills in the details.:) Also quite interesting is that Kelvin's age for the Earth matched the independent calculation for the age of the Sun (gravity; virial theorem), adding to Darwin's frustration. Multiple lines of evidence are sometimes just coincidental, just not often. :)

grapes
2018-May-24, 05:20 PM
Why would this be the case? Uranium is heavy. Or is it because the outer 2km comprises a volume for its shell > the core volume?
I'm no expert, but this link ( https://earthscience.stackexchange.com/questions/4798/what-percent-of-the-earths-core-is-uranium ) gives its reasoning for concluding:


This means that relative to solar system abundances, all three of these elements should be strongly enhanced in the Earth's crust, slightly depleted in the Earth's mantle, and strongly depleted in the Earth's core.

The three are potassium, uranium, and thorium

Strange
2018-May-24, 05:24 PM
I guess its a good thing uranium isn't concentrated in the core or it might go critical. (Not intended completely seriously)

George
2018-May-24, 06:17 PM
I'm no expert, but this link ( https://earthscience.stackexchange.com/questions/4798/what-percent-of-the-earths-core-is-uranium ) gives its reasoning for concluding: That almost eschews obfuscation. :) I found other sources agreeing with the claim but with little explanation, though I'm not spending a lot of time on it. I think it may be that only potassium can combine with iron to allow it to sink into the core, and the other radioactive elements do combine with lighter elements, which may keep them from sinking as much, I suppose. More likely is that meteorite data ratios are used to determine these things and potassium comes up very high in meteorites compared to the surface, so core concentration is one explanation for it.

This article (https://www.berkeley.edu/news/media/releases/2003/12/10_heat.shtml) addresses the above, and suggests to me that the other elements are higher in concentration for the surface than found in meteorites, so less in the core, no doubt is the logic. [This assumes Earth's formation region was similar to the asteroid belt's region for radioactive elements, which isn't illogical, I suppose.]

Hornblower
2018-May-24, 08:42 PM
Uranium and thorium are highly reactive chemically, and the crust is vastly enriched in them compared with the universe as a whole.

Ken G
2018-May-25, 02:26 AM
That was kind of my thinking in the first place. It failed to get the materials it needed for fusion.That would be part of the story, but not all of it, because you also need very high temperature. That's the sense to which Jupiter is a "failed star," because it has the hydrogen, but not high enough temperature. You could then say that the Earth is a doubly failed star, but it starts to get pretty far fetched when it's that far from being a star!

DaCaptain
2018-May-25, 03:28 AM
That would be part of the story, but not all of it, because you also need very high temperature. That's the sense to which Jupiter is a "failed star," because it has the hydrogen, but not high enough temperature. You could then say that the Earth is a doubly failed star, but it starts to get pretty far fetched when it's that far from being a star!

Hmm, when a star forms is it always a fusion reaction? Are there such things as fission stars?

Ken G
2018-May-25, 06:06 AM
Hmm, when a star forms is it always a fusion reaction? Are there such things as fission stars?It's always fusion, yes. Brown dwarfs are defined as not fusing normal hydrogen but fusing deuterium, and even those are not officially stars (though many regard them as a type of star).

Jens
2018-May-25, 06:07 AM
The only suggestions for any significant level of fusion in the core I've seen come from cold fusion advocates and are not backed by credible evidence.

Yes, that sounds right I suppose. I was basing what I wrote on a paper (https://www.nature.com/articles/srep37740) that I thought was in Nature Communications, but now I see it's Scientific Reports, so not very significant.

Dubbelosix
2018-Jun-01, 07:57 PM
The way I understand it, Earth is the product of what happens to a failed star.... the star fails, loses enough energy to finally inflate, and hopefully go supernova. The Earth is what the failed star has regurgitated.

Dubbelosix
2018-Jun-01, 07:59 PM
Also, as Grapes has mentioned, a ''failed star'' usually has a specific terminology any way.

PetersCreek
2018-Jun-01, 08:43 PM
The way I understand it, Earth is the product of what happens to a failed star.... the star fails, loses enough energy to finally inflate, and hopefully go supernova. The Earth is what the failed star has regurgitated.

The way you (mis)understand it is not mainstream science. The Space/Astronomy Questions and Answers subforum is where folks get mainstreams answers to their questions. ATM responses are not allowed.

Dubbelosix
2018-Jun-01, 08:48 PM
The way you (mis)understand it is not mainstream science. The Space/Astronomy Questions and Answers subforum is where folks get mainstreams answers to their questions. ATM responses are not allowed.

Ok... but where is my non-mainstream answer? We are leftovers of a star that went supernova a long time ago.

Jens
2018-Jun-02, 10:37 AM
The way I understand it, Earth is the product of what happens to a failed star.... the star fails, loses enough energy to finally inflate, and hopefully go supernova. The Earth is what the failed star has regurgitated.

You asked what is non-mainstream. It might simply be that you are misinformed or are using terminology incorrectly. A failed star does not go supernova, because a failed star is understood as "an object that came close to becoming a star but failed to get fusion going." Such an object will never go supernova. It is very large stars that become supernova at the end of their lives, so they are very successful stars. For example, the sun will not become a supernova because it is not massive enough. And I also wonder what you mean by "hopefully." It's a simple process, not something that one hopes for. In fact, if you are a civilization that is located near the star, then "hopefully" it will not go supernova...

And it is true that some of the elements on the earth are from supernova or perhaps neutron star mergers (I guess), but not everything is. I think that the hydrogen and helium may be primordial, but I could be wrong about this.

Dubbelosix
2018-Jun-02, 04:02 PM
You asked what is non-mainstream. It might simply be that you are misinformed or are using terminology incorrectly.


No offense, but people need to start reading more carefully. I was sparing the persons feelings by trying to get on even ground, I even said in the following post that the terminology he was using was mumbo jumbo in the contexts he had given.

Dubbelosix
2018-Jun-02, 04:02 PM
I am well aware of what is mainstream and what isn't.

Swift
2018-Jun-02, 06:05 PM
Ok, let's stop the side conversation. Thanks,

Ken G
2018-Jun-03, 02:23 PM
The issue seems to be the difference between a "failed" star and a "dying" star, as opposed to not using "star" language at all. If one wishes, one way to frame this issue is to say that any spread out high-mass ball of material is destined, as it loses heat and contracts, to end up as either a "failed star" (if it reaches its quantum mechanical ground state before ever undergoing significant fusion) or a "dead star" (if it does reach fusion, but then runs out of fuel). If one is to use that lens, one says every astrophysical object is currently either a star, a failed star, or a dying/dead star. Someone else might then bemoan the overuse of anthropomorphisms and analogies in place of precise language, but to each his/her own.

George
2018-Jun-04, 05:46 PM
Wouldn’t it be handy to have a snazzy word that simply means non-star? Then we would have two separate categories of objects: Star types from O1 down; Non-star types from BD to perhaps meteoroids.

This would let failure to not be an option. :)

DaCaptain
2018-Jun-14, 10:13 AM
If you replace "fusion" with "fission," then your thinking is correct. Note that fusion releases heat from building larger nuclei from smaller ones (like hydrogen into helium in stars), whereas fission releases heat by breaking up very large nuclei (like uranium and plutonium). There isn't hydrogen and helium in Earth's core, and the temperature is not high enough anyway, so it's not so much failing at fusion as it is succeeding at fission.

I had been thinking about this for a while and it seems that fusion is the more likely of the two to have happened. In order for a earth sized clump of uranium or plutonium to form and then spontaneously start a fission reaction seems out of the ordinary. Look at all the stars that are out there. Are any fission??? Why would fusion only be confined to star formation? Aren't the earth, the sun, and all the planets of our solar system approximately the same age and formed from the same soup.

Hornblower
2018-Jun-14, 01:15 PM
I had been thinking about this for a while and it seems that fusion is the more likely of the two to have happened. In order for a earth sized clump of uranium or plutonium to form and then spontaneously start a fission reaction seems out of the ordinary. Look at all the stars that are out there. Are any fission??? Why would fusion only be confined to star formation? Aren't the earth, the sun, and all the planets of our solar system approximately the same age and formed from the same soup.

As has been said before, the Earth is not hot enough inside to induce a significant amount of exothermic fusion of light elements, and never has been. In ordinary stars there certainly is radioactive decay of uranium and thorium taking place, but these elements are only on the order of one part in a billion of their total mass, so the contribution to the star's luminosity is negligible. The ample amount of hydrogen fusion is what keeps them hot and stable for a long time. For Earth, where the fusion, if any, is negligible, the decay of uranium and thorium is a significant source of internal heat.

DaCaptain
2018-Jun-29, 05:38 PM
It's always fusion, yes. Brown dwarfs are defined as not fusing normal hydrogen but fusing deuterium, and even those are not officially stars (though many regard them as a type of star).

This post has been bugging me for a while. If all stars are fusion, how is it that earth starts a fission reaction rather than fusion? Isn't fusion more prolific through out the cosmos?
Which is easier to create?

George
2018-Jun-29, 05:54 PM
This post has been bugging me for a while. If all stars are fusion, how is it that earth starts a fission reaction rather than fusion? Isn't fusion more prolific through out the cosmos?
Which is easier to create? It is easy to cause fission, but fusion requires extreme conditions to take place. Uranium can split apart naturally, or if hit by a tiny neutrino or larger particle. For a single atom, this is barely noticeable. A controlled fission reaction takes more effort but nothing compared to fusion.

Stars that form from clouds will include whatever tiny amount of fissionable atoms were in the cloud. Planets have a higher concentration of these only because the lighter gasses can't be held by the planet's much weaker gravity. But the energy generated in a star by decaying atoms is peanuts compared to the energy generated by its collapse from a gigantic cloud fragment into a compressed "small" ball. Only with enough mass will the core temperatures rise high enough for hydrogen to combine in one or more ways to make helium. With enough mass, due to fusion, a star is born.

Ken G
2018-Jun-30, 12:08 AM
This post has been bugging me for a while. If all stars are fusion, how is it that earth starts a fission reaction rather than fusion? Isn't fusion more prolific through out the cosmos?
Which is easier to create?
Fusion only releases energy when the nuclei are smaller than iron, and fission only releases energy when the nuclei are larger than iron. So which you get is entirely a matter of composition-- stars are made of small nuclei, rocky planets, large ones. And as pointed out, fusion requires high temperature because nuclei repel, fission does not.

grapes
2018-Jun-30, 04:31 PM
Fusion only releases energy when the nuclei are smaller than iron, and fission only releases energy when the nuclei are larger than iron. So which you get is entirely a matter of composition-- stars are made of small nuclei, rocky planets, large ones. And as pointed out, fusion requires high temperature because nuclei repel, fission does not.
Or, typically, "fission bombs" are triggered by "fusion bombs." The easiest way to set up the extreme conditions necessary.

Ken G
2018-Jun-30, 04:48 PM
I see what you mean, but I think you reversed it!

grapes
2018-Jun-30, 05:43 PM
I see what you mean, but I think you reversed it!
D'oh! yes

DaCaptain
2018-Aug-17, 03:03 PM
Or, typically, "fission bombs" are triggered by "fusion bombs." The easiest way to set up the extreme conditions necessary.


I see what you mean, but I think you reversed it!

Isn't this a paradoxical situation? Without heavy metals there can be no fission, but heavy metals are created from fusion reactions created by exploding stars. One can't exist without the other. Which came first?

George
2018-Aug-17, 03:20 PM
Isn't this a paradoxical situation? Without heavy metals there can be no fission, but heavy metals are created from fusion reactions created by exploding stars. One can't exist without the other. Which came first? Only one of those is the "star". ;) [It's not paradoxical, however, since metals are not required for fusion unless a H-bomb is the goal.]

Shaula
2018-Aug-17, 04:04 PM
Isn't this a paradoxical situation? Without heavy metals there can be no fission, but heavy metals are created from fusion reactions created by exploding stars. One can't exist without the other. Which came first?
As George says fission is not required for fusion. Fusion, however, requires such large temperatures and pressures that the simplest way for us to generate these when using fusion as a weapon in via the most powerful weaponised explosive we can have, i.e. a fission reaction. See https://en.wikipedia.org/wiki/Thermonuclear_weapon for the details on the configuration and a discussion about how it works.

Luckily for us the Sun and other stars doesn't need help creating the required conditions for fusion, nor does it need to operate as a small package suitable for delivery via a missile. It can generate the conditions for fusion and fuse away quite happily without heavy metals.

Edit to add - although small amounts of what astronomers refer to as metals are helpful for stars - see https://en.wikipedia.org/wiki/Stellar_population#Population_III_stars vs the other two main stellar populations for the differences in stars with and without metals.