JOURNEY TO THE CENTER OF THE EARTH
Jules Verne wrote about a human journey to the center of the earth. However,
his and other science fiction on the subject was based on false
ideas about what the earth was like. This one is based on current
Well, not by people, only instruments, and maybe not to the center
but only to the core. Consider a 400 meter long rod of tungsten.
Tungsten is enough heavier than ordinary rock that the pressure at the
bottom of the rod is enough greater than the ambient pressure plus the
compressive strength of ordinary rock. Therefore, the rod will sink,
maybe close to the center of the earth. The object is to instrument
the rod to report back to geophysicists on the surface about the
composition and other measurable properties of the layers it passes.
A number of questions arise.
- Is 400 meters, a rough calculation, the right length? Will
it penetrate better if it is pointed?
- What diameter must it have so that it won't be held up by
friction on its sides? What about buckling?
- How fast will it sink? Presumably it will sink slower as
it gets deeper and the gravitational attraction of the earth below
it lessens. The attraction is proportional to the distance from
the center, so it won't slow down very fast.
- Presumably it won't melt, because the melting point of
tungsten is higher than that of the layers through which it passes.
- It will be best if its instruments can function at ambient
temperature and pressure, since it will be difficult to maintain
an instrument compartment at surface temperature and pressure. Is
- What are the instruments? (1) temperature and pressure.
(2) seismometer. (3) Backscatter from a radioactive source as is
used in oil well logging. Multiple sources will be wanted.
(4) Chemical analysis of the layers it passes.
- What is the power source? Presumably a nuclear reactor powered
but it must have a T1 greater than ambient, and a
T2 at ambient or somewhat higher, so it will be a
different kind of nuclear reactor and a different kind of heat engine
than is used on the surface.
- How does information get back to the surface? (1) The
penetrator trails a cable. This seems chancy. (2) Information is coded
in neutrinos produced by an accelerator. This would require quite
a large neutrino detector, but who says this project would be cheap.
(3) Sound waves, possibly from explosions. If none of these worked,
maybe seismic waves would bounce off it detectably, at least giving
its current location.
I hope to provide some numbers in a future web page, but it would be better
if they were provided by someone with better qualifications than mine.
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