Micro-pixel Metrology for Precision Astrometry

Exo-planet detection has taken a rapid progress after the Kepler and several ground-based missions, thanks to the improvements of the observational techniques, which brought us increasingly sensitive detection and characterization. Among those exciting results, we now know that planets around the stars are common in the universe, but their physical and orbital properties are much more diverse than originally imagination. More and more giant planets or short-period planets are found according to the latest statistics of the exoplanets, but few of them are earth-alike, with a special regard to rocky planets orbiting in the habitable zone (HZ) of Sun alike stars. In this paper - a Space Astrometry mission to Search for the Terresrial Exo-Planets (SAIL / STEP) - has been proposed to enter a new phase in exoplanetary science by delivering an enhanced capability of detecting small planets at and beyond 1 AU. We will introduce our critical technique to calibrate the focal plan up to micro-pixel level aiming at the micro-arcsecond space astrometry on nearby stars.