Global asymmetry of the heliosphere Merav Opher ∗ , Edward C. Stone † , Paulett C. Liewer ∗∗ and Tamas Gombosi ‡ ∗ George Mason University, 4400 University Drive, Fairfax, VA 22030 † California Institute of Technology, Pasadena, CA 91125 ∗∗ Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109 ‡ Center for Space Environment Modeling, University of Michigan, Ann Arbor, MI Abstract. Opher et al. [1] showed that an interstellar magnetic field parallel to the plane defined by the deflection of interstellar hydrogen atoms can produce a north/south asymmetry in the distortion of the solar wind termination shock. This distortion is consistent with Voyager 1 and Voyager 2 observations of the direction of field-aligned streaming of the termination shock particles upstream the shock. The model also indicates that such a distortion will result in a significant north/south asymmetry in the distance to the shock and the thickness of heliosheath. The two Voyager spacecraft should reveal the nature and degree of the asymmetry in the termination shock and heliosheath. PACS: 96.50.Xy,96.60.-j,96.60.Iv INTRODUCTION After 27 years of anticipation, Voyager 1 crossed the inward moving termination shock (TS) at 94 AU and is now exploring the heliosheath [2, 3, 4]. The twin Voyager spacecraft are probing the northern and southern hemispheres of the heliosphere. As Voyager 1 crossed the TS and began exploring the heliosheath it has become increasingly clear that this previously unexplored region is full of surprises. Using in situ spacecraft data to constrain the shape of the heliosphere is challenging because they are single point observations. For a quantitative global understanding of the three dimensional structure of the heliosphere, it is necessary to use modeling in conjunction with observations to probe this region. In mid 2002, Voyager 1 began observing strong beams of energetic termination shock particles (TSPs) streaming outward along the spiral magnetic field. The strong upstream TSP beams were observed much of the time until Voyager 1 crossed the shock at 94 AU in December 2004. Jokipii et al. [5] and Stone et al. [4] suggested that the upstream beaming resulted from a non-spherical shock. For a spherical shock, Voyager 1 would observe upstream TSPs streaming inward along the magnetic field. With a non-spherical shock, Voyager 1 could be connected to the TS along magnetic field lines that crossed the TS (the source of TSPs) and then crossed back into the supersonic solar wind. In order to know Voyager 1 measurements in 2002 it is important to understand the shape of the heliosphere. The interaction of the solar system with the local interstellar medium requires an intensive modeling effort because this problem is inherently three dimensional and involves solar and interstellar magnetic fields, ionized and neutral atoms, and cosmic rays[6, 7]. The size and shape of the heliosphere will depend on the properties of both the solar wind and the local interstellar medium. 45 Downloaded 01 Dec 2006 to 131.215.240.9. Redistribution subject to AIP license or copyright, see http://proceedings.aip.org/proceedings/cpcr.jsp CP 858, Physics of the Inner Heliosheath, edited by J. Heerikhuisen, V. Florinski, G. P. Zank, and N. V. Pogorelov © 2006 American Institute of Physics 978-0-7354-0355-0/06/$23.00