Magnetic fields and plasma perpetually flow out from the Sun in all directions, filling the solar system; this flow is the solar wind. Embedded within the solar wind are planetary magnetospheres: bubbles which remain separate from the solar wind due to the internal magnetic field of a planet. The magnetopause describes the boundary between the solar wind and the magnetosphere. Surrounding the magnetopause, another boundary, the bow shock, is formed due to the sudden slowing of the fast-flowing solar wind as it hits the magnetosphere. The shapes and sizes of a planet's magnetopause and bow shock are in constant flux, driven by changes in the solar wind and in the planetary magnetosphere itself. At Jupiter, which has a particularly dynamic magnetosphere, the changes in the magnetopause and bow shock are dramatic, but are not well understood. Here we present new models of Jupiter's magnetopause and bow shock using spacecraft measurements and solar wind models. The sizes of both the magnetosphere and the bow shock are smaller than previously thought, meaning that missions to Jupiter, such as extit{Juno}, likely enter the solar wind---leaving the magnetopause and bow shocks in the process---much more frequently than previously expected.