[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.

[TallGuyShort]

On top of which gravity is going to lessen as you get to the center of mass, so even a little resistance will eventually become extremely significant...

[privong]

Only 100 km down, the gravitational acceleration would not be reduced by very much. Assuming the Earth is spherical and has uniform density, the probe would only be below ~3% of the mass and would be less than 2% closer in distance. So the acceleration felt by the probe would only vary by a few percent.

[4ad]

At 100km, the gravitational acceleration is actually higher than at the surface.

http://www.wolframalpha.com/input/?i=gravitational+accelerat...

In fact, it increases until 3500km below the surface (2800km radius).

http://en.wikipedia.org/wiki/Gravity_of_Earth#mediaviewer/Fi...