Astrophysics and Space Sciences Transactions www.astrophys-space-sci-trans.net 1810-6528 1810-6536 1 1 2005 10.5194/astra-1-29-2005 http://www.astrophys-space-sci-trans.net/1/29/2005/ http://www.astrophys-space-sci-trans.net/1/29/2005/astra-1-29-2005.html http://www.astrophys-space-sci-trans.net/1/29/2005/astra-1-29-2005.pdf 29 34 2005-12-09 Interpretation of Pioneer 10 heliospheric Ly α glow data obtained beyond 30 AU D. L. Judge V. V. Izmodenov M. Gruntman P. Gangopadhyay University of Southern California, Los Angeles, CA 90089, USA Moscow State University, Department of Aeromechanics and Gas Dynamics, School of Mechanics and Mathematics, Moscow, 119899, Russia Space Research Institute (IKI), Russian Academy of Sciences Institute for Problems in Mechanics, Russian Academy of Sciences The Pioneer 10 (P10) Ly α dataset is the only dataset that is available for the study of the very local interstellar medium (VLISM) in the downstream direction relative to the incoming interstellar neutral hydrogen flow, at very large distances from the sun. Selected P10 data obtained in 1984 and 1986 at distances between 31.81 to 32.25 and 37.29 to 37.74 AU have been used to estimate the local interstellar neutral hydrogen and proton densities. State of the art, stationary neutral-plasma and radiative transfer models have been used in the interpretation of the data. No stationary VLISM heliospheric model was found that best fitted both the P10 1984 data and the 1986 data. The failure to find a single best fit model is most probably due to the fact that the heliospheric model used here did not incorporate time-dependence and interstellar magnetic field effects.