Planet solar wind around itself called the magnetosphere, which the wind cannot penetrate. The magnetosphere can be much larger than the planet itself. In contrast, non-magnetized planets have only small magnetospheres induced by interaction of the ionosphere with the solar wind, which cannot effectively protect the planet. Of the eight planets in the Solar System, only Venus and Mars lack such a magnetic field. In addition, the moon of Jupiter Ganymede also has one. Of the magnetized planets the magnetic field of Mercury is the weakest, and is barely able to deflect the solar wind. Ganymede's magnetic field is several times
Social gravity a manner "analogous in all cases, by which the center of gravity in the solar system" held the planets in their orbits. In making this analogy, Pownall's notion of 'social gravity' drew upon earlier visions of social cohesion, particularly ideas of sociability in eighteenth-century Britain. These ideas, in turn, were often predicated upon Stoic notions of cosmopolitanism, expressed by the key term oikeiôsis, in order to stress the "moral" imperative for like-minded humans to forge bonds dedicated to the common good. Social gravity Social gravity was an application of Newtonian gravity to the system of commerce influence. For instance, in