We use a nonstationary generalization of the higher-order structure function
technique to investigate statistical properties of the magnetic field
fluctuations recorded by MESSENGER spacecraft during its first flyby
(01/14/2008) through the near Mercury's space environment, with the emphasis on
key boundary regions participating in the solar wind -- magnetosphere
interaction. Our analysis shows, for the first time, that kinetic-scale
fluctuations play a significant role in the Mercury's magnetosphere up to the
largest resolvable time scale ~20 s imposed by the signal nonstationarity,
suggesting that turbulence at this planet is largely controlled by finite
Larmor radius effects. In particular, we report the presence of a highly
turbulent and extended foreshock system filled with packets of ULF
oscillations, broad-band intermittent fluctuations in the magnetosheath,
ion-kinetic turbulence in the central plasma sheet of Mercury's magnetotail,
and kinetic-scale fluctuations in the inner current sheet encountered at the
outbound (dawn-side) magnetopause. Overall, our measurements indicate that the
Hermean magnetosphere, as well as the surrounding region, are strongly affected
by non-MHD effects introduced by finite sizes of cyclotron orbits of the
constituting ion species. Physical mechanisms of these effects and their
potentially critical impact on the structure and dynamics of Mercury's magnetic
field remain to be understood.Comment: 46 pages, 5 figures, 2 table
