The MICROSCOPE mission: first results of a space test of the Equivalence Principle

According to the Weak Equivalence Principle, all bodies should fall at the same rate in a gravitational field. The MICROSCOPE satellite, launched in April 2016, aims to test its validity at the ${10}^{-15}$ precision level, by measuring the force required to maintain two test masses (of titanium and platinum alloys) exactly in the same orbit. A non-vanishing result would correspond to a violation of the Equivalence Principle, or to the discovery of a new long-range force. Analysis of the first data gives $\delta\rm{(Ti,Pt)}= [-1 \pm 9 ($\mathrm{s}\mathrm{t}\mathrm{a}\mathrm{t}$) \pm 9 ($\mathrm{s}\mathrm{y}\mathrm{s}\mathrm{t}$)] \times 10^{-15}$(1$\sigma$ statistical uncertainty) for the titanium-platinum E"otv"os parameter characterizing the relative difference in their free-fall accelerations.