The inner planets, Mercury, Venus, Earth and Mars, are made up of silicate rock and heavy metals such as iron and nickel, whereas the outer planets, Jupiter, Saturn, Uranus and Neptune, are made up mostly of gases, according to Universe Today. The outer planets are subdivided into gas giants, comprised mostly of hydrogen and helium, and ice giants, comprised mostly of methane, ammonia and water.Know More
Despite being made up mostly of gases, the outer planets have a rock core. However, they are still less dense and located further away from the sun than the inner or terrestrial planets. Astronomers are able to to determine how planets formed by studying the structure of the solar system and other younger planetary systems that are in varying stages of development.
The dominant theory, according to HowStuffWorks, states that solar wind emanating from the sun blew light elements, mostly gases, away into the outer orbits. Gravity then drew these elements in causing them to form giant balls. The discovery of hot Jupiters in 1995, however, put a dent in this theory. Hot Jupiters are a type of gas giant that orbit very close to the sun. Astronomers theorize that such planets form far away from the sun and then move closer through orbital migration.Learn more about Planets
The inner planets of the solar system are all relatively close to the sun. They are also all relatively similar to each other in size, mass, density and other physical properties. Unlike the outer planets, the inner planets are small, dense and warm.Full Answer >
The inner planets of the solar system are small, rocky worlds that have very few moons. The outer planets are composed primarily of gases and are much larger than the inner planets. All four of the outer planets have a system of rings and are orbited by multiple moons.Full Answer >
The characteristics that the outer planets have in common include their large size and their large number of moons when compared with the inner, or terrestrial, planets. They also lack solid surfaces, and as far as astronomers know, none are capable of supporting life. For example: Jupiter and Saturn are "gas giants" with atmospheres made up largely of hydrogen and helium, while Neptune and Uranus are called "ice giants" because their atmospheres also contain ammonia, methane and water ices.Full Answer >
The outer planets Jupiter, Saturn, Uranus and Neptune all have shorter days than Earth. Among the terrestrial planets, Mars has a slightly longer day than Earth at 24 hours 37 minutes. Mercury's day lasts 59 Earth days, while a day on Venus lasts 243 Earth days.Full Answer >