  The Near-Earth binary asteroid Didymos was the target of a planetary defense
demonstration mission DART in September 2022. The smaller binary component,
Dimorphos, was impacted by the spacecraft in order to measure momentum transfer
in kinetic impacts into rubble piles. DART and associated Earth-based
observation campaigns have provided a wealth of scientific data on the
Didymos-Dimorphos binary. DART revealed a largely oblate and ellipsoidal shape
of Dimorphos before the impact, while the post-impact observations suggest that
Dimorphos now has a prolate shape. Here we add those data points to the known
properties of small binary asteroids and propose new paradigms of the radiative
binary YORP (BYORP) effect as well as tidal dissipation in small binaries. We
find that relatively spheroidal bodies like Dimorphos made of small debris may
experience a weaker and more size-dependent BYORP effect than previously
thought. This could explain the observed values of period drift in several
well-characterized binaries. We also propose that energy dissipation in small
binaries is dominated by relatively brief episodes of large-scale movement of
(likely surface) materials, rather than long-term steady-state tidal
dissipation. We propose that one such episode was triggered on Dimorphos by the
DART impact. Depending on the longevity of this high-dissipation regime, it is
possible that Dimorphos will be more dynamically relaxed in time for the Hera
mission than it was in the weeks following the impact.
