On the two approaches to the data analysis of the Cassini interplanetary relativity experiment

Abstract

We compare two theoretical approaches to the data analysis of the Cassini relativity experiment based on the Doppler tracking and the time delay technique that were published correspondingly by Kopeikin et al. [S.M. Kopeikin, A.G. Polnarev, G. Schäfer, I.Yu. Vlasov, Phys. Lett. A 367 (2007) 276] and by Bertotti et al. [B. Bertotti, N. Ashby, L. Iess, Class. Quantum Grav. 25 (2008) 045013]. Bertotti et al. believed that they found a discrepancy with our paper and claimed that our analysis was erroneous. The present Letter elucidates, however, that the discrepancy is illusory and does not exist. The two techniques give the same result making it evident that the numerical value of the PPN parameter γ measured in the Cassini experiment is indeed affected by the orbital motion of the Sun around the barycenter of the solar system.