Sending a probe to the Earth's core?

[SpaceGuy50]

Will we ever be able to actually send a probe to the Earth's core?

 

[DaveC426913]

"Ever" is a loooong time.

 

[OAQfirst]

SpaceGuy, I'd like to point you at Wikipedia for some of your curiosity. For travel to the planet's core, see this article:

http://en.wikipedia.org/wiki/Travel_to_the_Earth's_core

Take these articles with a grain of salt for they are publicly edited, but for general information-digging they can be fun.

 

[D H]

http://en.wikipedia.org/wiki/Travel_to_the_Earth's_core

Take these articles with a grain of salt for they are publicly edited, but for general information-digging they can be fun.

A bit off topic, but

People wonder why some disallow use of wikipedia as a source at any education level. The cited entry is prima facie evidence of why this is so.

 

[OAQfirst]

A bit off topic, but

People wonder why some disallow use of wikipedia as a source at any education level. The cited entry is prima facie evidence of why this is so.

Didn't you notice the Teenage Mutant Ninja Turtles reference?

Actually, I focused on the very first two paragraphs:

Travel to the Earth's center, though not currently considered scientifically possible, is a popular theme in science fiction. Some subterranean fiction involves travel to the Earth's center, either finding a Hollow Earth or the Earth's molten core.

Though no scientists have seriously proposed travel to the Earth's center, planetary scientist David J. Stevenson suggested sending a probe to the core as a thought experiment.[1][2] So far, the deepest humans have drilled is just over 12 kilometers, (7.62 miles), in the Kola Superdeep Borehole.[3]

 

[DaveC426913]

A bit off topic, but

People wonder why some disallow use of wikipedia as a source at any education level. The cited entry is prima facie evidence of why this is so.

Depends on how you look at it.

What's significant is what isn't there, i.e. it's an extremely short article because there's very little of anything serious to say about the subject.

 

[jamesb-uk]

The deepest penetration ever into the Earth was 12.2km. That project was stopped due to lack of funds. The Earth's crust is 30-40km thick, and the centre of the inner core is about 6000km down. We'd need a LOT of money and time to get that far. There would be many problems with it- heat of the rocks, radiation etc.

And why would we? What could we gain from going down that deep? I can't see why anyone would put in so many resources, unless we had a major shortage of iron and nickel on the crust? I suppose it could be a bit like going on the moon or climbing everest- really just to say we can. I don't know what the people who dug down 12km did it for though.

 

[RonL]

If you consider the energy return in trying to keep a drill bit cool, you might get a free cost to drill. (other than the cost of materials)

Energy related there might be great rewards. What might be the risk of blowout holes??
I think the affect of energy withdrawl from the total heat of the Earth would be miniscule.

Travel ? totally out of reason.

 

[jamesb-uk]

If you consider the energy return in trying to keep a drill bit cool, you might get a free cost to drill. (other than the cost of materials)

Energy related there might be great rewards. What might be the risk of blowout holes??
I think the affect of energy withdrawl from the total heat of the Earth would be miniscule.

Travel ? totally out of reason.

Theoretically, but that would have to be in the far future, as we couldn't possibly make an alloy which could surve such temperatures. We can get energy from heat via hot rocks in places with volcanic activity- in Iceland in particular, they use geothermal energy, where they pump water down to the rocks about 4km down, and it comes back up as steam. It would have to be deeper than that in non-volcanic areas, but in order to get a lot of energy from it, we wouldn't have to enter the mantle, let alone the inner core.

 

[RonL]

Theoretically, but that would have to be in the far future, as we couldn't possibly make an alloy which could surve such temperatures. We can get energy from heat via hot rocks in places with volcanic activity- in Iceland in particular, they use geothermal energy, where they pump water down to the rocks about 4km down, and it comes back up as steam. It would have to be deeper than that in non-volcanic areas, but in order to get a lot of energy from it, we wouldn't have to enter the mantle, let alone the inner core.

If I'm not mistaken, there is no alloy at present that will not melt at the internal temperature of a jet engine, it is all in how you hold the heat away from the metals.

I don't think it is possible to reach the core, but only for other reasons.

 

[jamesb-uk]

If I'm not mistaken, there is no alloy at present that will not melt at the internal temperature of a jet engine, it is all in how you hold the heat away from the metals.

I don't think it is possible to reach the core, but only for other reasons.

The temperature of the inner core is about 5500K. The melting point of tungsten, with one of the highest melting points is about 3500K. The temperature of the hottest part of a jet engine is very roughly, depending on the type etc, 3000K. So it is possible, although I don't think tungsten is used.

How do you think we could cool the probe? We couldn't use air as the mantle is too viscous, and then we'd have the problem of piping it down there. If we used anything with a melting point of much less than 5500K, if it is in contact with the magma, it would melt very quickly. It would be impossible to convect heat away quickly enough, partly because of the viscosity of the magma, and partly because of the distance the substance would have to travel before it reached the cool surface. The only reason a jet engine is cooled is because it has a ready supply of very cold air coming in at very fast rates.

I'm not saying the temperature is the only problem here, but that it is a major one.

 

[RonL]

The temperature of the inner core is about 5500K. The melting point of tungsten, with one of the highest melting points is about 3500K. The temperature of the hottest part of a jet engine is very roughly, depending on the type etc, 3000K. So it is possible, although I don't think tungsten is used.

How do you think we could cool the probe? We couldn't use air as the mantle is too viscous, and then we'd have the problem of piping it down there. If we used anything with a melting point of much less than 5500K, if it is in contact with the magma, it would melt very quickly. It would be impossible to convect heat away quickly enough, partly because of the viscosity of the magma, and partly because of the distance the substance would have to travel before it reached the cool surface. The only reason a jet engine is cooled is because it has a ready supply of very cold air coming in at very fast rates.

I'm not saying the temperature is the only problem here, but that it is a major one.

I know very little other than some exposure to drilling oil wells, a typical oil well uses a heavy mud mixed to a certain viscosity needed to supply lift to the debris produced by the drill bit, it also lubricates the drill stem, and as well cools and lubricates the bit.

AFAIK temperatures at 20,000' are hot enough to produce steam, and going beyond a solid formation is beyond anything I can think of, in my mind.

 

[Ophiolite]

People wonder why some disallow use of wikipedia as a source at any education level. The cited entry is prima facie evidence of why this is so.

You don't think much of Nature as a reliable publication then? An unusual viewpoint, but to each his own.

 

[Borek]

People wonder why some disallow use of wikipedia as a source at any education level. The cited entry is prima facie evidence of why this is so.

It occurred to me that PF is no better than wikipedia - after all, anoyone can register and answer questions about GR.

 

[Skyhunter]

Wikipedia is a much better source than PF.

Although a well cited post here is the similar to a well cited Wiki.

 

[diogenesNY]

Will we ever be able to actually send a probe to the Earth's core?

Well, it occurs to me that as long as we are not wedded to the idea of drilling holes, there might be ways to address this.

There has been sonic (sonar-like I think) probing and seizmic data modeling that purports to explore and expose the inner core of the earth. Some of this data is currently fueling the debate over what happens to subducted crustal slabs (where do they go? do they drop to the core or keep fluttering around the upper mantle? contrversial/inconclusive).

I guess what I am getting at is that physically boring a hole to the inner core, although a much used premise in many thought experiments, seems to represent an extreme level of difficulty. Although the mantle is 'plastic' I don't think it is overly meaningful to describe a physical object desending within it to examine the inner core (although this is perhaps possible, given some far out interpretations of the original question - e.g. bury an instrument package with a very long lived power source and very tough case by embedding it in the crust on the 'under' side of a subduction fault... track its movements over millions of years).

Indirect probing, however, is possible and going on now. Still controversy as to what the data gathered so far means and even how to interpret it. Still other things about the core are inferred from observed effects. We can probe the core lots... getting there is the difficult part.

diogenesNY

P.S. For an entirely different take on this issue, please see the Firesign Theatre album: "Everything You Know is Wrong"

 

[jamesb-uk]

There has been sonic (sonar-like I think) probing and seizmic data modeling that purports to explore and expose the inner core of the earth. Some of this data is currently fueling the debate over what happens to subducted crustal slabs (where do they go? do they drop to the core or keep fluttering around the upper mantle? contrversial/inconclusive).

I thought that the subducted crust simply becomes part of the mantle- the mantle is, after all, very hot rock, magma. I didn't think there was a debate about it.

Indirect probing, however, is possible and going on now. Still controversy as to what the data gathered so far means and even how to interpret it. Still other things about the core are inferred from observed effects. We can probe the core lots... getting there is the difficult part.

But what can they learn from this? That plate tectonics is correct? What more is there to learn?

 

[DaveC426913]

But what can we learn from this? That plate tectonics is correct? What more is there to learn?

Uh, isn't that like asking "we know weather/volcanism/evolution/any-other-science occurs, what more is there to learn?"

 

[jamesb-uk]

Uh, isn't that like asking "we know weather/volcanism/evolution/any-other-science occurs, what more is there to learn?"

Perhaps it was badly phrased. I just wanted to ask what the researchers' aims for this research were, which I assumed were to confirm our theories.

 

[DaveC426913]

Perhaps it was badly phrased. I just wanted to ask what the researchers' aims for this research were, which I assumed were to confirm our theories.

It would be to learn all we can so we can refine our theories. We don't know that much about what goes on.

 

[Ophiolite]

I thought that the subducted crust simply becomes part of the mantle- the mantle is, after all, very hot rock, magma. I didn't think there was a debate about it.

There is no debate about it because your statement is flawed. Magma is molten rock. The mantle is not molten. There are thought to be small portions of it where partial melting occurs. This is unlikely to exceed 10% by volume of these portions. The only continuously molten part of the interior is the outer core.

 

[diogenesNY]

I thought that the subducted crust simply becomes part of the mantle- the mantle is, after all, very hot rock, magma. I didn't think there was a debate about it.

The mantle isn't magma though... it is a plastic under incredible pressures that moves fluidly but only very slowly.

FWIW, I do vaguely recall having much the same view that crustal slabs melted and merged with the mantle in an ongoing cycle of recirculation. I seem to also recall learning this in my undergrad intro geology class about 20 years ago... but that would conflict with the basic physics of the circumstances of the slabs... so I guess my memory is a bit flawed.

Anyway, the dispute as to the fate of the slabs (i.e. dropping to the bottom of the mantle vs flitting about the upper mantle... held above a certain depth by a pressure/bouyancy boundry is something that I have read about in some fairly recently authored books and seen cited in some discussions. I will need to dig up the titles, but that is easily done. As for the more basic issue of the general fate of crustal slabs, I cite the following passage from the textbook _now_ used at Duke for an intro undergrad geology course:

"At convergent plate boundries, the downgoing plate grinds aginst the base of the overriding plate, a process that generates large earthquakes. These earthquakes occur fairly close to the Earth's surface, so some of them trigger massive destruction in coastal cities. But earthquakes also happen in downgoing plates at greater depths, deep below the overriding plate. In fact, geologists have detected earthquakes within downgoing plates to a depth of 660km; the belt of earthquakes in a downgoing plate is called a Wadati-Benioff zone, after its two discoverers (-> Fig. 4.14a).

At depths greater than 660km, conditions leading to earthquakes evidently do not occur. Recent evidence, however, indicates that some downgoing plates do continue to sink below a depth of 660km--they just do so without generating earthquakes. In fact, studies suggest that the lowe mantle may be a graveyard for old subducted plates (->Fig 4.14b)"

Fig's 1.14 a&b illustrate the above with color drawings

Page 87, Earth: Portrait of a Planet, Stephen Marshak, Second edition.

Also, ditto on what Ophiolite says... partial melting is localized and can lead to rising magma, but that is not the default state of the mantle.

diogenesNY

 

[JaredJames]

Sorry to bring up an old thread, but I've always wondered, if we've never been there, how do we know the core is 5500K? What do we actually know about the core that we can be fairly certain about?

 

[SpaceGuy50]

Sorry to bring up an old thread, but I've always wondered, if we've never been there, how do we know the core is 5500K? What do we actually know about the core that we can be fairly certain about?

If we were actually able to visit the core directly, we could very well see some/many surprises.