  Exoplanet surveys have confirmed one of humanity's (and all teenagers') worst
fears: we are weird. If our Solar System were observed with present-day Earth
technology -- to put our system and exoplanets on the same footing -- Jupiter
is the only planet that would be detectable. The statistics of exo-Jupiters
indicate that the Solar System is unusual at the ~1% level among Sun-like stars
(or ~0.1% among all stars). But why are we different?
  Successful formation models for both the Solar System and exoplanet systems
rely on two key processes: orbital migration and dynamical instability. Systems
of close-in super-Earths or sub-Neptunes require substantial radial inward
motion of solids either as drifting mm- to cm-sized pebbles or migrating
Earth-mass or larger planetary embryos. We argue that, regardless of their
formation mode, the late evolution of super-Earth systems involves migration
into chains of mean motion resonances, generally followed by instability when
the disk dissipates. This pattern is likely also ubiquitous in giant planet
systems. We present three models for inner Solar System formation -- the
low-mass asteroid belt, Grand Tack, and Early Instability models -- each
invoking a combination of migration and instability.
  We identify bifurcation points in planetary system formation. We present a
series of events to explain why our Solar System is so weird. Jupiter's core
must have formed fast enough to quench the growth of Earth's building blocks by
blocking the flux of inward-drifting pebbles. The large Jupiter/Saturn mass
ratio is rare among giant exoplanets but may be required to maintain Jupiter's
wide orbit. The giant planets' instability must have been gentle, with no close
encounters between Jupiter and Saturn, also unusual in the larger (exoplanet)
context. Our Solar System system is thus the outcome of multiple unusual, but
not unheard of, events.
