  The asteroid (3200) Phaethon is known to be the parent body of the Geminids,
although meteor showers are commonly associated with the activity of periodic
comets. What is most peculiar to the asteroid is its comet-like activity in the
ejection of micrometer-sized dust particles at every perihelion passage, while
the activity of the asteroid has never been identified outside the
near-perihelion zone at $0.14~\mathrm{au}$ from the Sun. From the theoretical
point of view, we argue that the activity of the asteroid is well explained by
the electrostatic lofting of micrometer-sized dust particles with the aid of
mobile alkali ions at high temperatures. The mass-loss rates of
micrometer-sized particles from the asteroid in our model is entirely
consistent with the values inferred from visible observations of Phaethon's
dust tail. For millimeter-sized particles, we predict three orders of
magnitudes higher mass-loss rates, which could also account for the total mass
of the Geminid meteoroid stream by the electrostatic lofting mechanism.
