Exo-Jupiters and Saturns from two Gaia-like missions
  Detection and orbit determination for thousands of planets with periods up to about 40 years would be obtained by astrometry from two Gaia-like missions, results which cannot be obtained by any other mission, planned or proposed. A billion stars of all spectral types will be surveyed. A comprehensive knowledge about heavy planets with these periods, reaching well beyond the snow line of any system, will lead to a better understanding of the formation and evolution of planets, also in the habitable zone. 
Erik H{\o}g, (Niels Bohr Institute)
astro-ph.IM