The Kuiper Belt
The Kuiper Belt was named after the astronomer Gerrit Pieter Kuiper (1905 – 1973), who predicted this region based on his studies. At the time, orbital calculations of medium-period comets suggested that they must have originated from a region beyond Neptune's orbit.
The Kuiper Belt is the second asteroid belt in the Solar System. It begins behind Neptune's orbit and extends at a distance of 30 to 55 AU from the Sun. It is estimated to contain about 70,000 objects with a diameter of more than 100 km. The average distance between objects in the Kuiper Belt is roughly the same as the distance between the Earth and the Sun (150 million km i.e. 1 AU). Unlike in the asteroid belt, much more water ice can be found on asteroids in the Kuiper belt because of the great distance to the Sun. This ice forms the tail of comets as they approach the sun.
Eris, Haumea and Makemake
Eris was named after the Greek goddess of discord. It takes about 557 years to orbit the Sun. Its orbit is inclined by 44° to the ecliptic and is very elliptical in shape. Its distance from the Sun varies between 38 and 97 AU. Eris is almost as big as Pluto, but a lot heavier.
Haumea was named after a Hawaiian fertility goddess. It takes about 285 years to orbit the Sun. Its orbit is inclined 28° to the ecliptic and elliptical in shape. Its distance from the Sun varies between 35 and 52 AU. Haumea rotates on its own axis in just four hours and is therefore highly elliptical in shape. It is almost as wide as Pluto but has only one-third of its mass.
Makemake was named after the creation deity of Easter Island. It takes about 308 years to orbit the Sun. Its orbit is inclined 29° to the ecliptic and elliptical in shape. Their distance from the Sun varies between 38 and 53 AU. Makemake revolves around itself in a little less than a day.
All these celestial bodies are dwarf planets. It is believed that more than 100 of them are located in the Kuiper Belt.
The Heliopause and the Oort Cloud
The better astronomers' instruments become, the further out the boundary of our solar system seems to shift. Today, the boundary of the solar system is drawn based on the influence of the sun. A series of concentric boundaries is formed by the solar wind – charged particles that are ejected by the sun. The solar wind penetrates the solar system to a distance of about 95 AU. There, the solar wind begins to mix with particles from other stars. The heliopause, where the solar wind becomes indistinguishable from the particles of other stars, is located at a distance of 122 AU. If you want to follow the Planetary Trail to the Heliopause, then the next stop would be between Pinswang and Füssen.
The outermost, still hypothetical limit of the solar system is the Oort cloud. This is the greatest distance that long-period comets reach on their way away from the Sun. Since only a few comets fly to the Sun from so far away, it is possible that many more of them form a spherical envelope around our solar system so far out. That would be the limit of the Sun's gravitational influence, at a distance of up to 100,000 AU, or about 1.6 light-years. If you want to follow the Planetary Trail to the outer boundary of the Oort Cloud, then you need to dress warmly, because this station would then be at the North Pole.