Meteoritic whitlockite containing excess fission tracks has a large concentration of excess neutron-rich xenon isotopes which is 25 times that calculated from the track density. The isotopic spectrum is identical to that calculated previously for the Pasamonte achondrite. These results uniquely associate this spectrum with in situ fission. Identification of the fissioning nucleus as ${\mathrm{Pu}}^{244}$ gives ${\mathrm{Pu}}^{244}$/${\mathrm{U}}^{238}$ ≅ 1/30 at the time of xenon retention. Neither "sudden" nor "uniform" nucleosynthetic models give consistent solutions for ${\mathrm{Pu}}^{244}$/${\mathrm{U}}^{238}$ and ${\mathrm{U}}^{235}$/${\mathrm{U}}^{238}$.

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