  Inspired by the close-proximity pair of planets in the Kepler-36 system, we
consider two effects that may have important ramifications for the development
of life in similar systems where a pair of planets may reside entirely in the
habitable zone of the hosting star. Specifically, we run numerical simulations
to determine whether strong, resonant (or non-resonant) planet-planet
interactions can cause large variations in planet obliquity---thereby inducing
large variations in climate. We also determine whether or not resonant
interactions affect the rate of lithopanspermia between the planet pair---which
could facilitate the growth and maintenance of life on both planets. We find
that first-order resonances do not cause larger obliquity variations compared
with non-resonant cases. We also find that resonant interactions are not a
primary consideration in lithopanspermia. Lithopanspermia is enhanced
significantly as the planet orbits come closer together---reaching nearly the
same rate as ejected material falling back to the surface of the originating
planet (assuming that the ejected material makes it out to the location of our
initial conditions). Thus, in both cases our results indicate that
close-proximity planet pairs in multihabitable systems are conducive to life in
the system.
