  Recently Sahu et al., using the Hubble Space Telescope to monitor stars in
the direction of the old globular cluster M22, detected six events in which
otherwise constant stars brightened by ~50% during a time of <1 day. They
tentatively interpret these unresolved events as due to microlensing of
background bulge stars by free-floating planets in M22. I show that if these
spike events are due to microlensing, the lensing objects are unlikely to be
associated with M22, and unlikely to be part of a smoothly distributed Galactic
population. Thus either there happens to be a massive, dark cluster of planets
along our line-of-sight to M22, or the spike events are not due to
microlensing. The lensing planets cannot be bound to stars in the core of M22:
if they were closer than 8 AU, the lensing influence of the parent star would
have been detectable. Moreover, in the core of M22, all planets with
separations > 1 AU would have been ionized by random stellar encounters. Most
unbound planets would have escaped the core via evaporation which
preferentially affects such low-mass objects. Bound or free-floating planets
can exist in the outer halo of M22; however, for reasonable assumptions, the
maximum optical depth to such a population falls short of the observed optical
depth, tau ~ 3x10^{-6}, by a factor of 5-10. Therefore, if real, these events
represent the detection of a significant free-floating Galactic planet
population. The optical depth to these planets is comparable to and mutually
exclusive from the optical depth to resolved events measured by microlensing
survey collaborations toward the bulge, and thus implies a similar additional
mass of lensing objects. Such a population is difficult to reconcile with both
theory and observations.
