  A major question in dynamical systems is to understand the mechanisms driving
global instability in the 3 Body Problem (3BP), which models the motion of
three bodies under Newtonian gravitational interaction. The 3BP is called
restricted if one of the bodies has zero mass and the other two, the primaries,
have strictly positive masses $m_0,m_1$. We consider the Restricted Planar
Elliptic 3 Body Problem (RPE3BP) where the primaries revolve in Keplerian
ellipses. We prove that the RPE3BP exhibits topological instability: for any
values of the masses $m_0,m_1$ (except $m_0=m_1$), we build orbits along which
the angular momentum of the massless body experiences an arbitrarily large
variation provided the eccentricity of the orbit of the primaries is positive
but small enough.
  In order to prove this result we show that a degenerate Arnold Diffusion
Mechanism, which moreover involves exponentially small phenomena, takes place
in the RPE3BP. Our work extends the result obtained in \cite{MR3927089} for the
a priori unstable case $m_1/m_0\ll1$, to the case of arbitrary masses
$m_0,m_1>0$, where the model displays features of the so-called \textit{a
priori stable} setting.
