&ITMICROSCOPE&IT 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 nonvanishing 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(Ti, Pt) = [-1 +/- 9(stat) +/- 9(syst)] x 10(-15) (1 sigma statistical uncertainty) for the titanium-platinum Eotvos parameter characterizing the relative difference in their free-fall accelerations.