When did the giant-planet orbital instability happen?
In plain words
Models suggest Jupiter, Saturn, Uranus and Neptune once went through a violent rearrangement of their orbits. Whether this happened within the first 100 million years or about 700 million years later is still debated.
Precise statement
Determine the epoch of the giant-planet instability relative to gas-disk dispersal: early (within about 100 Myr) or late (about 500 to 700 Myr), using constraints from Jupiter trojan binaries, asteroid and meteorite impact ages, terrestrial-planet orbital excitation and lunar basin chronology. An answer is an instability time with uncertainty consistent with all dynamical and chronological constraints.
What would settle it
A consistent set of dynamical survival constraints (trojan binaries, terrestrial planet orbits) and radiometric impact ages that exclude one of the two epochs.
Status in the literature
Most dynamical studies since 2018 favour an early instability, but the interpretation of lunar impact ages remains disputed.