  We have conducted a differential elemental abundance analysis of
unprecedented accuracy (0.01 dex) of the Sun relative to 11 solar twins from
the Hipparcos catalogue and 10 solar analogs from planet searches. We find that
the Sun shows a characteristic signature with a
  ~20% depletion of refractory elements relative to the volatile elements in
comparison with the solar twins. The abundance differences correlate strongly
with the condensation temperatures of the elements. This peculiarity also holds
in comparisons with solar analogs known to have close-in giant planets while
the majority of solar analogs found not to have such giant planets in radial
velocity monitoring show the solar abundance pattern. We discuss various
explanations for this peculiarity, including the possibility that the
differences in abundance patterns are related to the formation of planetary
systems like our own, in particular to the existence of terrestrial planets.
