Encounters involving planetary systems in birth environments: the
  significant role of binaries
  Most stars form in a clustered environment. Both single and binary stars will
sometimes encounter planetary systems in such crowded environments. Encounter
rates for binaries may be larger than for single stars, even for binary
fractions as low as 10-20 per cent. In this work, we investigate scatterings
between a Sun-Jupiter pair and both binary and single stars as in young
clusters. We first perform a set of simulations of encounters involving wide
ranges of binaries and single stars, finding that wider binaries have larger
cross sections for the planet's ejection. Secondly, we consider such
scatterings in a realistic population, drawing parameters for the binaries and
single stars from the observed population. The scattering outcomes are diverse,
including ejection, capture/exchange and collision. The binaries are more
effective than single stars by a factor of several or more in causing the
planet's ejection and collision. Hence, in a cluster, as long as the binary
fraction is larger than about 10 per cent, the binaries will dominate the
scatterings in terms of these two outcomes. For an open cluster of a stellar
density 50 pc$^{-3}$, a lifetime 100 Myr and a binary fraction 0.5, we estimate
that of the order of 1 per cent of the Jupiters are ejected, 0.1 per cent
collide with a star, 0.1 per cent change ownership and 10 per cent of the
Sun-Jupiter pairs acquire a stellar companion during scatterings. These
companions are typically 1000s of au distant and in half of the cases (so 5 per
cent of all Sun-Jupiter pairs), they can excite the planet's orbit through
Kozai--Lidov mechanism before stripped by later encounters. Our result suggests
that the Solar System may have once had a companion in its birth cluster.
