George Mason University
Pinning Down the Direction and Magnitude of the Local Interstellar Magnetic Field
Magnetic effects are ubiquitous and known to be crucial in space physics and astrophysical media. We have now the opportunity to probe these effects in the outer heliosphere with the two spacecraft Voyager 1 and 2. Voyager 1 crossed, in Dec 2004, the termination shock and is now in the heliosheath. On August 30, 2007 Voyager 2 crossed the termination shock, providing us for the first time in-situ measurements of the subsonic solar wind in the heliosheath. With the recent in-situ data from Voyager 1 and 2 the numerical models are forced to confront their models with observational data. Our recent results indicate that magnetic effects, in particular the interstellar magnetic field, are very important in the interaction between the solar system and the interstellar medium. We summarize here our recent work that shows that the interstellar magnetic field affects the symmetry of the heliosphere that can be detected by different measurements. We combined radio emission and energetic particle streaming measurements from Voyager 1 and 2 with extensive state-of-the art 3D MHD modeling, to constrain the direction of the local interstellar magnetic field. The orientation derived is a plane ~ 60°-90° from the galactic plane. This indicates that the field orientation differs from that of a larger scale interstellar magnetic field, thought to parallel the galactic plane. As a result of the interstellar magnetic field the solar system is asymmetric being pushed in the southern direction. We present results from recently developed 5 fluids MHD model (4 neutral fluids and 1 ionized fluid). The presence of neutral H, has the effect of diminishing the global heliospheric symmetries. With a stronger interstellar field, however, the symmetries are increased. We discuss these results and discuss our work on pinning down the intensity of the interstellar magnetic field.