  We explore the Yarkovsky effect on small binary asteroids. While significant
attention has been given to the binary YORP effect, the Yarkovsky effect is
often overlooked. We develop an analytical model for the binary Yarkovsky
effect, considering both the Yarkovsky-Schach and planetary Yarkovsky
components, and verify it against thermophysical numerical simulations. We find
that the Yarkovsky force could change the mutual orbit when the asteroid's spin
period is unequal to the orbital period. Our analysis predicts new evolutionary
paths for binaries. For a prograde asynchronous secondary, the Yarkovsky force
will migrate the satellite towards the location of the synchronous orbit on
~100 kyr timescales, which could be faster than other synchronization processes
such as YORP and tides. For retrograde secondaries, the Yarkovsky force always
migrates the secondary outwards, which could produce asteroid pairs with
opposite spin poles. Satellites spinning faster than the Roche limit orbit
period (e.g. from ~4h to ~10h) will migrate inwards until they disrupt,
reshape, or form a contact binary. We also predict a short-lived equilibrium
state for asynchronous secondaries where the Yarkovsky force is balanced by
tides. We provide calculations of the Yarkovsky-induced drift rate for known
asynchronous binaries. If the NASA DART impact broke Dimorphos from synchronous
rotation, we predict that Dimorphos's orbit will shrink by \dot a ~ 7 cm/yr,
which can be measured by the Hera mission. We also speculate that the Yarkovsky
force may have synchronized the Dinkinesh-Selam system after a possible merger
of Selam's two lobes.
