  We describe the circumstances that led to the discovery of Kepler-36b, and
the subsequent characterization of its host planetary system. The Kepler-36
system is remarkable for its physical properties: the close separation of the
planets, the contrasting densities of the planets despite their proximity, and
the short chaotic timescale. Its discovery and characterization was also
remarkable for the novelty of the detection technique and for the precise
characterization due to the large transit-timing variations caused by the close
proximity of the planets, as well as the precise stellar parameters due to
asteroseismology. This was the first multi-planet system whose transit data was
processed using a fully consistent photometric-dynamical model, using
population Markov Chain Monte Carlo techniques to precisely constrain system
parameters. Amongst those parameters, the stellar density was found to be
consistent with a complementary, concurrent asteroseismic analysis. In a first,
the 3D orientation of the planets was constrained from the lack of
transit-duration variations. The system yielded insights into the composition
and evolution of short-period planet systems. The denser planet appears to have
an Earth-like composition, with uncertainties comparable to the highest
precision rocky exoplanet measurements, and the planet densities foreshadowed
the rocky/gaseous boundary. The formation of this system remains a mystery, but
should yield insights into the migration and evolution of compact exoplanet
systems.
