Discovery Space: Orbits of Celestial Bodies
The objects of the solar system come in all kinds of shapes and can be classified by size, type, and orbit.
The sun and all the celestial objects orbiting it, including the planets, make up the solar system. Their movements are more or less in the same plane and almost circular, except Mercury, which has a more elongated orbit. A top-down view onto the solar system shows it has several well-defined regions.
The regions of the solar system
The planets Mercury, Venus, Earth, and Mars travel along the inside orbits. These planets are mainly rocky and due to this similarity with the Earth are also referred to as terrestrial or telluric planets. None of these planets, except the Earth, offer suitable habitats for living creatures. The only planet to come close to a state of sustaining Earthlike life is Mars.
The planets traveling along the outer orbits are Jupiter, Saturn, Uranus, and Neptune. These are much larger than the terrestrial planets and consist mostly of hydrogen and helium gas. Hence, they are often referred to as the gas giants. The two planet groups are separated between Mars’ and Jupiter’s orbits by an asteroid belt of mostly irregularly shaped rocks, only a few of which are larger than about 60 miles (100 km). The dwarf planet Pluto and several smaller objects circle outside of Neptune’s orbit in the Kuiper belt.
Several comets also originate from here. Their glowing tails often become visible when they move into the inner solar system. The Oort cloud is thought to be located even further outside. It encloses the planetary system like a shell, creating a boundary. The cloud consists of icy celestial bodies spread over a vast area. This is where comets accumulate, and from time to time are diverted into the solar system.
THE LIFE ZONE
The Earth orbits the sun at the “right-distance for warming: It is not too cold and not too hot. This, along with the right atmospheric pressure, allows water to occur not only as ice or vapor, but also as liquid.
This is a precondition for life forms we are familiar with, although some microorganisms survive in extreme conditions. The “life zone- is the distance belt around a star that allows water to be liquid, and is dependent on solar radiation intensity.
BASICS
THE SOLAR SYSTEM emerged from a huge, circling cloud of gas and dust about 4.6 billion years ago.
THE EARTH orbits around the sun at a distance of almost 93 million miles (150 million km).