A Nuclear Probe to Explore Earth’s Interior

[ridgeguy]

The post states that tungsten "...has a low corrosion rate at elevated temperatures." This is not accurate.

Tungsten oxidizes in air beginning around 600°C and as the temperature increases, the tungsten oxide layer scales off, exposing underlying metal to further oxidation. (see, for example, http://labfus.ciemat.es/AR/2011/C_004/AM_4x.pdf)

Tungsten is great for high temperature use in vacuum, neutral (the inert gases) or reducing environments (hydrogen, for example). You can use it nearly up to its melting point in those conditions if you aren't too dependent on structural integrity.

In oxidizing environments (air, oxygen, water, halogens, silicates, etc.) it fails quite rapidly. Molten rock is replete with chemical species that react with tungsten at elevated temperatures.

At 2000°C, the tungsten blanket covering the Co60 heat source would be corroded away, I'll guess, within a week of launch on its journey to the center of the earth.

Although it would be incredibly costly, they might have better luck with iridium or rhenium.

Nevertheless, a fun mission to think about.

[Natsu]

> A self-sinking probe is basically a dumb probe measuring less than 100 cm in diameter - a lump of nuclear waste encapsulated in a tungsten sphere and sunk into the ground.

Even more so if you wonder if it couldn't be a way to dispose of waste. Also, if corrosion was an issue, perhaps they could coat it with something?

[bediger4000]

A Caltech professor, David Stevenson, proposed a temperature-resistant probe immersed in a blob of molten iron: Stevenson, David J. Mission to Earth's Core - A Modest Proposal. Nature, 423, 239-240, 2003a. No radioactivity necessary, and the PDF is here: http://mathcs.albion.edu/~mbollman/Honors/ToTheCore!.pdf

[RachelF]

What prevents it from cooling down?

[entangledqubit]

A patent for a similar device from back in the 60s: http://www.google.com/patents/US3115194

Happened to see it while archiving the inventor's papers. :)

[wmeredith]

What a fascinating proposition. FYI: This blog article is from 2013 and is about scientific papers written in 2008 and 2005. A few minutes of cursory Googling turns up nothing else.

[valarauca1]

It was actually used as the basis of a Young Adult book in 2005 [1] or a very similar idea. The book uses a large molten ore body created from explosive charges.

[1] https://en.wikipedia.org/wiki/Artemis_Fowl:_The_Opal_Decepti...

[cpeterso]

"... and they were never heard from again!"

[ChuckMcM]

Did this go anywhere? The only papers if find that reference the original ideas (2005 and 2008) mention nuclear waste that melts itself into the Earths core.

[ISL]

Probably not. That's a scary thing to build. Cobalt-60 gammas are hard to shield, and 2000K is really hot. The laws of physics don't forbid building such a thing, but I wouldn't want to be in the same building with it.

Okay, so you have something that's so self-heating that it'll easily melt rock. In fact, it's hot enough that it self-liquifies quickly at STP. Cobalt reacts weakly with oxygen, but you'll still have to be careful with it in air, so you'll have to seal it in something; at 2000K, there are only a few materials with which you can hold and seal it, tungsten being one. Also, it's radioactive, and the tungsten sphere you put it in isn't nearly sufficient to stop the gammas.

So, you get your tungsten sphere all ready to go, let the cobalt liquify itself, pour it into the sphere, and then lower/drop it into a borehole. Better not be any water down there, or it might come back up.

Once you've got it doing it's melting thing and it's really deep at the bottom of a borehole, it probably can't hurt anyone.

I can't imagine a funding agency being ballsy-enough to fund it, and _really_ can't imagine a nuclear regulatory agency being interested in letting you build a source that could get itself so thermally hot.

TL;DR -- lots could go wrong.

[S4M]

The article also suggests using the probe to analyze the composition of other planets. Is that doable? It seems pretty tough to me to carry on a space ship a nuclear probe hot enough to melt rocks.

[jerf]

If we're to the point where we're even considering this, presumably we're in a position to obtain the materials from either local sources, or possibly asteroid sources. This presumes a level of tech much higher than our current one since at our current one we can barely land probes that can drill semi-aimlessly into rocks. (And don't get me wrong, that's a hell of an achievement that gives me the Warm Science Fuzzies that we can pull it off... but it's also a long way from being able to do this sort of probe on other planets.)

[jessriedel]

If you're going to carry a probe powerful enough to melt rocks on a spaceship, the probe better damn well be nuclear powered. There's no other way to get the energy density to make the launch costs feasible.

[rdmcfee]

With the accelerating change in the earth's magnetic field it would be fantastic to drop a few of these bad boys and see what's actually going on down there.

[gipp]

Wouldn't get anywhere near the dynamo, sadly.

[ars]

"Subsequent re-crystallisation of the molten material will generate intense acoustic signals."

Why would it make any noise?

[ejr]

I imagined to be like ice which does make crackling noises when it freezes due to expansion, except cooling rocks will shrink causing the same. Re-solidifying rock would probably sound louder and the acoustic signature may travel further.

[spingsprong]

Would this produce a new volcano?

Or would the magma just freeze as it travels through the relatively cool hole?

[dredmorbius]

My read is that the rock would re-fuse above the probe, so no:

"Heat generated from the decay of radioactive cobalt-60 allows the probe to melt its way into the Earth. The probe is estimated to melt down to a depth of 20 km in ~1 year. As the probe descents deeper, the rate of descent will gradually slow until the probe reaches a depth of 100 km after ~30 years. By melting its way into the Earth, the probe will leave behind a wake of molten material. Subsequent re-crystallisation of the molten material will generate intense acoustic signals."

[curtis]

This sounds like a more practical version of David J. Stevenson's 2003 earth probe proposal: http://news.nationalgeographic.com/news/2003/05/0514_030514_...

[cromwellian]

Seems that the technique would also work on Europa to melt its way into the ocean underneath the ice.

[panzi]

But if there really is live down there, how do you then explain to them that you just dropped some nuclear waste into their ocean?

[Crito]

It has definitely been suggested: http://en.wikipedia.org/wiki/Cryobot http://www.jpl.nasa.gov/releases/2002/release_2002_6.html

[gulpahum]

This sounds like a controlled version of the China syndrome. http://en.wikipedia.org/wiki/Nuclear_meltdown#China_Syndrome

[grecy]

> As the probe descents deeper, the rate of descent will gradually slow until the probe reaches a depth of 100 km after ~30 years

The article doesn't mention - why will the probe stop descending?

[toomuchtodo]

Increase in density as you get closer to the core.

[msane]

What was that recent speculation based on seismic resonance about there possibly being a large amount of previously un-theorized water, rather than rock, somewhere in the interior?

[youaredoomed]

Why not place the sphere into a pre-made hole so it will make it to the center of the planet faster?

[jimmyswimmy]

A couple reasons, I'd bet - first, a hole wide enough to fit the probe is pretty unusual, and would be an expensive research project all on its own. Second, the probe near the surface will emit the largest signal, so you get some really good SNR data to calibrate your algorithms against. If you don't understand the signals you're receiving when it's shallow, you won't understand them any better when it's deep - a regime where we have more theories than data. Or maybe something else.

[nacnud]

Drop it into a volcano, for example?

[doctorKrieger]

why cant we dispose our nuclear waste in this way?

[cpeterso]

https://en.wikipedia.org/wiki/Deep_borehole_disposal

[mikeash]

I don't think most nuclear waste gets nearly hot enough.

[BorisMelnik]

if they get to the center they will find the gnomes, which won't end well.

[3327]

wow this is actually genius cheap and doable can some please forward this to Jeff Bezos?

[ars]

"transform some of the energy from radioactive decay"

Not so simple. You need a hot source and a cold sink to transform energy. Where's your cold sink? This thing is intended to melt what's around it, and the outside of the probe is not that different in temperature from the inside.

[gipp]

Erm. If it's melting the rock around it, then the rock is your cold sink. By the time the temperature of the rock catches up with the probe, it's already molten anyway.

[cperciva]

You need a hot source and a cold sink to transform energy.

Only if it's thermal energy. Given the small amount of power needed, they could easily use a betavoltaic generator.

[InclinedPlane]

Co-60 decays via beta (and then gamma) decay. It's a straightforward matter to convert the beta decay into electrical power.