A possible generation mechanism for the IBEX ribbon from outside the
  heliosphere
  The brightest and most surprising feature in the first all-sky maps of
Energetic Neutral Atoms (ENA) emissions (0.2-6 keV) produced by the
Interstellar Boundary Explorer (IBEX) is an almost circular ribbon of a
~140{\deg} opening angle, centered at (l,b) = (33{\deg}, 55{\deg}), covering
the part of the celestial sphere with the lowest column densities of the Local
Interstellar Cloud (LIC). We propose a novel interpretation of the IBEX results
based on the idea of ENA produced by charge-exchange between the neutral H
atoms at the nearby edge of the LIC and the hot protons of the Local Bubble
(LB). These ENAs can reach the Sun's vicinity because of very low column
density of the intervening LIC material. We show that a plane-parallel or
slightly curved interface layer of contact between the LIC H atoms (n_H = 0.2
cm^-3, T = 6000-7000 K) and the LB protons (n_p = 0.005 cm^-3, T ~ 10^6 K),
together with indirect contribution coming from multiply-scattered ENAs from
the LB, may be able to explain both the shape of the ribbon and the observed
intensities provided that the edge is < (500-2000) AU away, the LIC proton
density is (correspondingly) < (0.04-0.01) cm^-3, and the LB contains ~1% of
non-thermal protons over the IBEX energy range. If this model is correct, then
IBEX, for the first time, has imaged in ENAs a celestial object from beyond the
confines of the heliosphere and can directly diagnose the plasma conditions in
the LB.
