The misshapen solar system

Having traveled far beyond the planets in their 28.5-year journey, NASA’s two Voyager spacecraft are providing new information on the heliosphere, the teardrop-shaped bubble that separates the solar system from interstellar space (see the diagram for an orientation). At the May meeting of the American Geophysical Union and several other geoscience-related societies, Edward Stone of Caltech reported that the heliosphere is deformed, with the teardrop’s rounded edge bulging at the top (the northern hemisphere of the solar system) and squashed at the bottom (the southern hemisphere). Robert Decker of the Johns Hopkins University Applied Physics Laboratory explained that the asymmetry can be due to a weak interstellar magnetic field (about 10⁻⁵ the strength of Earth’s field) pushing on the southern hemisphere. The interstellar field even squashes the termination shock, the boundary at which the rapidly traveling solar wind slows down abruptly and piles up. Voyager 2’s measurements indicate...