[topspin]

Without guessing the mass cannot be "just as lethal" now as at any point in the past. Its lethality comes from decay of unstable isotopes. Radioactive decay has a half life so radiation inexorably falls with time and lethality necessarily falls with it.

[Retric]

That would be true if exactly one isotope decade into a stable isotope. With more complex decay chains etc that does not always apply.

Ex: A has a half life of 100 years and B has a half life of 10 years. If the sample starts at 100% A it will become more radioactive for the first few years until B reaches a steady state.

[Gibbon1]

The radiation is a bad thing. And the radioactive isotopes in the thing are also bad. Considering it's from what I've heard and what I expect, turning slowly to dust, staying away from it is a good idea.

[gargravarr]

Very. Which is why the NSC was built to isolate it for at least 100 years (presumably it will be reinforced regularly by successive generations). Nothing we can do except allow it to decay to safe levels over time.