NASA has captured an extraterrestrial space probe that has been in space for millions of years. The probe was operated by a kind of radionuclide battery, which on launch consisted of a pure block of plutonium-244. Now, the isotope ratio between thorium-232 and plutonium-244 is 1:1 due to the radioactive decay
How long was the probe in space? (Specify the time in millions of years and round it to the nearest integer.)
Details and Assumptions: