Stellar origin of the p-nuclei 92,94Mo and 96,98Ru
In plain words
A few proton-rich isotopes cannot be built by neutron capture, the route that makes most heavy elements, and the leading theory makes them by breaking up heavier nuclei with heat radiation in supernovae. That theory makes far too little molybdenum-92, molybdenum-94, ruthenium-96 and ruthenium-98, which are surprisingly common in the solar system.
Precise statement
92Mo, 94Mo, 96Ru and 98Ru make up roughly 15, 9, 5.5 and 1.9 percent of solar Mo and Ru, while gamma-process yields (photodisintegration of seed nuclei at $T \sim 2e9\ \text{to}\ 3e9\ \mathrm{K}$) in core-collapse supernovae and standard Type Ia models underproduce them by an order of magnitude or more relative to other p-nuclei. Identify the site or combination of sites (neutrino-driven proton-rich outflows, the nu p-process; Type Ia explosions of s-process-enriched white dwarfs; oxygen-carbon shell mergers in massive stars) that reproduces their solar abundances and the 92Mo/94Mo ratio with realistic nuclear rates.
What would settle it
Nucleosynthesis yields from self-consistent explosion or merger models, folded into galactic chemical evolution, that reproduce the solar Mo and Ru p-isotope abundances within a factor of 2 using measured proton- and $\alpha$-capture rates.
Status in the literature
Unverified note
3D models of oxygen-carbon shell mergers (2025-2026) are reexamining gamma-process yields; no site is yet accepted.