AAS 201st Meeting, January, 2003
Session 45. The Solar System
Poster, Tuesday, January 7, 2003, 9:20am-6:30pm, Exhibit Hall AB

## [45.09] Effect of the Pioneer Anomaly on Long-Period Comet Orbits

J. D. Anderson, S. Turyshev (Jet Propulsion Laboratory), M. M. Nieto (Los Alamos National Laboratory)

Radio tracking data from Pioneer 10 and 11 show an anomalous, constant, Doppler frequency drift that can be interpreted as an acceleration directed towards the Sun of aP = (8.74 ±1.33) \times 10-8 ~~{\rm cm/s}2, at heliocentric distances ~20-70 AU (Anderson et al., Phys. Rev. Lett. 81, 2858; Anderson et al., Phys. Rev. D 65, 082004). In the absence of any physical theory that predicts such an acceleration, the primary candidate remains systematic error generated by spacecraft systems. However, neither we nor anyone else has been able to find a viable spacecraft systematic that is both large enough and constant enough to explain the anomaly.

We show that the Pioneer anomaly, interpreted as a physical effect external to the spacecraft, can have profound implications for LP comet orbits. If the anomaly behaves as an ever-present constant force, it shifts the 364 1/aorig values for higher quality LP orbits (Marsden and Williams, Catalogue of Cometary Orbits 2001, 14th ed., SAO) to higher values, where a is the osculating semi-major axis in the Kepler ellipse. In addition, it eliminates all hyperbolic orbits. The Oort cloud becomes a narrow shell of comets at about 2500 AU with a thickness of about 400 AU. Two drag models also seem viable. In the first, the drag acceleration is proportional to the orbital speed V and in the second it is proportional to V2. In these models, comets entering the solar system on interstellar orbits become nearly parabolic on their first pass, as observed, and then undergo further evolution by drag and planetary perturbations. Large effects on short period comets such as Halley and Encke are avoided by assuming a hole in the resisting medium inside 10 or 20 AU, consistent with limited Pioneer data analysis in this region.

The work of J.D.A. and S.G.T was performed at the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration. M.M.N. acknowledges support by the U.S. DOE. J.D.A. acknowledges partial support as a 2002 Visiting Scientist at Monash University, Australia, under the sponsorship of Dr. A. J. R. Prentice, Department of Mathematics.