Our Solar System is a stellar-planetary unit consisting of the Sun; the eight planets and their satellites; the asteroids, comets, and meteoroids; and interplanetary dust and gas. The dimensions of this system are specified in terms of the mean distance from the Earth to the Sun, called the astronomical unit (AU). One AU is 150 million km. Pluto, which is not anymore counted as a planet, has an orbit at 39.44 AU from the Sun. Solar system is thus located inside the heliosphere created by the solar wind, which is estimated to reach beyond about 120 AU. The comets, however, achieve the greatest distance from the Sun; they have highly eccentric orbits ranging out to 50,000 AU or more.
Space physics is typically interested in the plasma environments found in the solar system, where in situ measurements can be performed. Especially the solar wind with interplanetary magnetic field and planets with internal magnetic fields (and thus also magnetospheres) and/or ionospheres are important. These are Mercury, Earth, Jupiter, Saturn, Uranus, and Neptune.
See also Wikipedia on solar system.