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

TL;DR

This paper compares two theoretical approaches to analyzing the Cassini relativity experiment data, clarifying that they produce consistent results and confirming the influence of the Sun's orbital motion on the measurement of the PPN parameter 'gamma'.

Contribution

It demonstrates that two previously debated analysis methods yield identical results, resolving a claimed discrepancy and clarifying the effect of solar orbital motion on the experiment.

Findings

Both approaches produce the same value for 'gamma'.

The Sun's orbital motion affects the measurement of the PPN parameter.

The discrepancy claimed in prior work is illusory.

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 in Phys. Lett. A 367, 276 (2007) and by Bertotti et al in Class. Quant. Grav. 25, 045013 (2008). Bertotti et al believed that they found a discrepancy with our paper and claimed that our analysis was erroneous. The present paper 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 'gamma' measured in the Cassini experiment is indeed affected by the orbital motion of the Sun around the barycenter of the solar system.