Solar System

The Solar System is also home to two regions populated by smaller objects. The which lies between Mars and Jupiter, is similar to the terrestrial planets as it is composed mainly of rock and metal. Beyond Neptune's orbit lie composed mostly of ices such as water, ammonia and methane. Within these two regions, five individual objects, and are recognized to be large enough to have been rounded by their own gravity, and are thus termed In addition to thousands of in those two regions, various other small body populations, such as and freely travel between regions.

The, a flow of from the Sun, creates in the known as the, which extends out to the edge of the scattered disc. The hypothetical which acts as the source for may also exist at a distance roughly a thousand times further than the heliosphere.

and the bound to it by all of which formed from the collapse of a giant approximately 4.6 billion years ago. Of the many objects that the Sun, most of the is contained within eight relatively solitary whose orbits are almost circular and lie within a nearly flat disc called the The four smaller inner planets, and also called the are primarily composed of rock and metal. The four outer planets, th, are substantially more massive than the terrestrials. The two largest, and are composed mainly of hydrogen and helium; the two outermost planets, and are composed largely of such as water, ammonia and methane, and are often referred to separately as "ice giants".