New independent analysis and interpretation of the Pioneer 10 and 11 Doppler data: Finding the origin of the Pioneer anomaly

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AU from the Sun has consistently indicated an anomalous, constant Doppler frequency drift. This blue-shifted signal uniformly changes with rate ¿¿ = (5.99 ± 0.01)·10¿9 Hz/s and has been interpreted as constant acceleration aPioneer = (8.74 ± 1.33) · 10¿10 m/s2 directed towards the Sun. This is the Pioneer Anomaly. Up to now no satisfactory explanation to this anomaly has been found. We propose to perform for the first time an improved independent analysis of the entire set of the Pioneer 10 and 11 radio-metric Doppler data from 1972 to 2002 corresponding to the distance range from 3 AU to 80 AU which is critical in order determine the nature of the anomalous acceleration. We propose: i) to use the capabilities at ZARM to perform the analysis of the navigational and instrumental data collected from the Pioneer spacecrafts in deep space, ii) to independently investigate the anomalous signal found in the Pioneer 10/11 Doppler data. If the presence of the anomaly is confirmed, we propose to i) confront the anomalous residuals with various models of small non¿gravitational forces, ii) calibrate the contribution of gas leaks and miss¿modeled maneuvers to the trajectory solution, iii) further address the issue of collimated thermal emission from the on¿board power sources, iv) characterize the anomaly in more detail, including temporal and distance dependency of the effect, and v) study the data focusing on the planetary fly-bys. JPL will make the data available to ZARM. In parallel, possible physical explanations of the found effect within the standard General Relativity shall be looked for. These include (i) investigation of mass distributions in the Solar system which lead to a constant acceleration, and (ii) investigation of the physics of the propagation of massive particles (the spacecrafts) and light (the radio signals) in the solar system embedded in the gravitational field of the galaxy, in the expanding universe including terms with the structure of a cosmological constant. Widely discussed long¿range Yukawa¿like modifications of gravity are also of interest to be included in these investigations. Particular emphasis shall be laid on the discussion of the difference between bound elliptic and escape hyperbolic orbits. This theoretical study, which may be called ¿local gravitational physics in the expanding universe¿, is of interest by itself. It is important to put the Pioneer Anomaly in the context of recent experimental advances in gravitation and cosmology. The flat rotation curves of spiral galaxies as well as results from gravitational microlensing surveys has led to the assumption of the existence of the mysterious Dark Matter, since no compelling argument exists for the other alternative, namely, that a fundamental modification is necessary in the Kepler-Newton-Einstein laws of gravitation. Similarly, the results of the study of type Ia supernovae, WMAP data and analysis of the Lyman-alpha forest data lines ¿ when compared with standard cosmological models ¿ have been interpreted in terms of the existence of the mysterious Dark Energy that leads to the acceleration of the universe, rather than a modification of the basic laws of gravitation. Should the Pioneer Anomaly prove to be a basic signature of the breakdown of the accepted laws of gravitation, its detailed study and verification by future space missions would have fundamental and far reaching consequences for gravitational physics and cosmology.