Interplanetary space is that part of outer space between planets in a solar system and its local star(s). Around any one planet, this space begins in the extended region where any amosphere, magnetic field and moons end, ceding dominance to the local star; in our case, the Sun.

The diffuse outer boundary of our interplanetary space is characterized by the heliopause, where the solar wind meets the interstellar medium, and by the Oort cloud, the region where comets originate. Closer in, there is the Kuiper belt, containing planetoids.

Earth is the third planet from the Sun, after Mercury and Venus. Next out, Mars is the last of the rocky planets with definite surfaces. Beyond it lie the four "gas giants": Jupiter, Saturn, Uranus and Neptune. The first two have some planet-sized moons. Last comes Pluto, whose classification as a planet is in dispute. NASA's New Horizons spacecraft will be the first terrestrial craft destined for Pluto.

Since planets have been discovered orbiting other stars in recent decades, we now know that there are other planetary systems, each with its own interplanetary space, a term which may be used even if there is only one planet. (See Stars with planets.) Each system presumably evolved from a primitive solar nebula. Most stars, and presumably most planetary systems, belong to galaxies, between which there is intergalactic space.

The space separating all astronomical bodies is characterized by a vacuum better than any experimentally produced on Earth, by the 2.7 K blackbody radiation left over from the Big Bang that created the Universe, and by cosmic rays, which include ionized atomic nuclei and various subatomic particles. There is also gas, plasma and dust.

Our solar system has an asteroid belt between the orbits of Mars and Jupiter which generates meteors, whose impact craters cover the surface of our Moon, and some other moons and planets, with more than 150 found on Earth.

Astronomy | Planets | Solar system | Moons

Espace interplanétaire | Starpplanētu vide | Przestrzeń międzyplanetarna | Межпланетное пространство