  We study the orbital properties of stars in four (published) simulations of
thick disks formed by: i) accretion from disrupted satellites, ii) heating of a
pre-existing thin disk by a minor merger, iii) radial migration and iv) gas
rich mergers. We find that the distribution of orbital eccentricities are
predicted to be different for each model: a prominent peak at low eccentricity
is expected for the heating, migration and gas-rich merging scenarios, while
the eccentricity distribution is broader and shifted towards higher values for
the accretion model. These differences can be traced back to whether the bulk
of the stars in each case is formed 'in-situ' or is 'accreted', and are robust
to the peculiarities of each model. A simple test based on the eccentricity
distribution of nearby thick disk stars may thus help elucidate the dominant
formation mechanism of the Galactic thick disk.
