The Solar Technique is also home to regions populated by smaller objects. The asteroid belt, which lies between Mars and Jupiter, is similar to the terrestrial planets as it consists chiefly of rock and metal. Beyond Neptune's orbit lie trans-Neptunian objects composed mostly of ices such as water, ammonia and methane. Within these regions, individual objects, Ceres, Pluto, Haumea, Makemake and Eris, are recognized to be huge to have been rounded by their own gravity, and are thus termed dwarf planets.[e] In addition to thousands of little bodies[e] in those regions, various other little body populations, such as comets, centaurs and interplanetary dust, freely travel between regions.
The Solar System[a] consists of the Sun and the astronomical objects bound to it by gravity, all of which formed from the collapse of a huge molecular cloud about two.6 billion years ago. Of the plenty of objects that orbit the Sun, most of the mass is contained within two comparatively solitary planets[e] whose orbits are circular and lie within a virtually flat disc called the ecliptic plane. The smaller inner planets, Mercury, Venus, Earth and Mars, also called the terrestrial planets, are primarily composed of rock and metal. The outer planets, the gas giants, are substantially more huge than the terrestrials. The largest, Jupiter and Saturn, are composed chiefly of hydrogen and helium; the outermost planets, Uranus and Neptune, are composed largely of ices, such as water, ammonia and methane, and are often referred to separately as "ice giants".Six of the planets and of the dwarf planets are orbited by natural satellites,[b] usually termed "moons" after Earth's Moon. Each of the outer planets is encircled by planetary rings of dust and other particles.
The solar wind, a flow of plasma from the Sun, creates a bubble in the interstellar medium known as the heliosphere, which extends out to the fringe of the scattered disc. The hypothetical Oort cloud, which acts as the source for long-period comets, may also exist at a distance roughly a thousand times further than the heliosphere.
The Solar System[a] consists of the Sun and the astronomical objects bound to it by gravity, all of which formed from the collapse of a huge molecular cloud about two.6 billion years ago. Of the plenty of objects that orbit the Sun, most of the mass is contained within two comparatively solitary planets[e] whose orbits are circular and lie within a virtually flat disc called the ecliptic plane. The smaller inner planets, Mercury, Venus, Earth and Mars, also called the terrestrial planets, are primarily composed of rock and metal. The outer planets, the gas giants, are substantially more huge than the terrestrials. The largest, Jupiter and Saturn, are composed chiefly of hydrogen and helium; the outermost planets, Uranus and Neptune, are composed largely of ices, such as water, ammonia and methane, and are often referred to separately as "ice giants".Six of the planets and of the dwarf planets are orbited by natural satellites,[b] usually termed "moons" after Earth's Moon. Each of the outer planets is encircled by planetary rings of dust and other particles.
The solar wind, a flow of plasma from the Sun, creates a bubble in the interstellar medium known as the heliosphere, which extends out to the fringe of the scattered disc. The hypothetical Oort cloud, which acts as the source for long-period comets, may also exist at a distance roughly a thousand times further than the heliosphere.