  At scales much larger than the ion inertial scale and the gyro-radius of
thermal protons, magnetohydrodynamic (MHD) theory is well equipped to describe
the nature of solar wind turbulence. The turbulent spectrum itself is defined
by a power-law manifesting the energy cascading process. A break in the
turbulence spectrum develops near ion scales, signaling the onset of energy
dissipation. The exact mechanism for the spectral break is still a matter of
debate. In this work, we use the 20 Hz \textit{MESSENGER} magnetic field data
during four planetary flybys at different heliocentric distances to examine the
nature of the spectral break in the solar wind. %By carefully selecting the
spacecraft trajectory, We relate the spectral break frequencies of the solar
wind MHD turbulence, found in the range of $0.3$ to $0.7$ Hz, with the
well-known characteristic spectral bump at frequencies $\sim 1$ Hz upstream of
planetary bow shocks. Spectral breaks and spectral bumps during three planetary
flybys are identified from the \textit{MESSENGER} observations, with
heliocentric distances in the range of $0.3$ to $0.7$ au. The
\textit{MESSENGER} observations are complemented by one \textit{MMS}
observation made at 1 au. We find that the ratio of the spectral bump frequency
to the spectral break frequency appears to be $r$- and $B$- independent. From
this, we postulate that the wavenumber of the spectral break and the frequency
of the spectral bump have the same dependence on the magnetic field strength
$|B|$. The implication of our work on the nature of the break scale is
discussed.
