The Apparent Anomalous, Weak, Long-Range Acceleration of Pioneer 10 and 11

TL;DR

This paper investigates the anomalous acceleration observed in Pioneer 10 and 11 spacecraft, analyzing Doppler data to estimate its magnitude and exploring potential causes like thermal emission.

Contribution

It provides updated estimates of the Pioneer spacecrafts' anomalous acceleration and critiques possible explanations, including thermal emission effects.

Findings

Estimated Pioneer 10 acceleration: ~7.5 x 10^{-8} cm/s^2

Doppler data analysis supports the existence of a small, constant Sunward acceleration

Thermal emission is suggested as a possible cause for the anomaly

Abstract

Recently we reported that radio Doppler data generated by NASA's Deep Space Network (DSN) from the Pioneer 10 and 11 spacecraft indicate an apparent anomalous, constant, spacecraft acceleration with a magnitude $\sim 8.5\times 10^{-8}$ cm s$^{-2}$, directed towards the Sun (gr-qc/9808081). Analysis of similar Doppler and ranging data from the Galileo and Ulysses spacecraft yielded ambiguous results for the anomalous acceleration, but it was useful in that it ruled out the possibility of a systematic error in the DSN Doppler system that could easily have been mistaken as a spacecraft acceleration. Here we present some new results, including a critique suggestions that the anomalous acceleration could be caused by collimated thermal emission. Based partially on a further data for the Pioneer 10 orbit determination, the data now spans January 1987 to July 1998, our best estimate of the average Pioneer 10 acceleration directed towards the Sun is $\sim 7.5 \times 10^{-8}$ cm s$^{-2}$.