Inner planets are those which are much closer to the sun compared to the other. Mars, on the other hand, is believed to have an iron-sulfur core and is … All are compact solid bodies. These planets move slowly as they are considered to be heavy. Smaller Density The Sun is a big ball of hydrogen powered by nuclear reactions. These four planets are mainly made up of rocks, which contain minerals based on inorganic substances and their derivatives like soil and dust. The cores of Mercury, Venus, and Earth are composed of iron-nickel. Earth is the only one of the inner planets to liquid oceans but some believe that Mars once did as well. It has a thin... Venus. Many of these were present in compounds with oxygen. They are mostly made up of silicate rock and metals and have solid surfaces. Compared to the four gas giant planets that make up the outer solar system, the inner planets all have... Rocky Surface. These four planets developed from small grains of dust that collided and stuck together to form pebbles, boulders, kilometer- and mile-sized planetesimals, and larger … Mars's... History. The four innermost planets in the Solar System (Mercury, Venus, Earth, and Mars) are sometimes called the "terrestrial" planets because of their proximity to Earth ("Terra" in Latin) and their similarity as compact solid bodies with rocky surfaces. When the solar system was forming, all planets, both inner and outer planets, in the beginning had nearly identical proportions of hydrogen and helium gases as well as rocks in their cores. Size Range. The Inner Solar System by Leslie Cargile The inner solar system is the name of the terrestrial planets and asteroid belt. The inner planets are made of rocks and metals and are called the terrestrial planets. The inner planets of the solar system are also called terrestrial planets, and include Mercury, Venus, Earth and Mars. Terrestrial is just a fancy way of saying rocky. Every inner planet has a core. Terrestrial Planets: Definition & Facts About the Inner Planets Mercury. The Inner Planets Structure. There were relatively few elements of any other kind in a solid state to form the inner planets. A massive concussion wave from the proto-Sun's initial ignition is thought to have blown away the thick atmospheres of the inner protoplanets but left the outer planets untouched. The elements in the Inner Planets are more closely packed together, causing them to be smaller and solid. They are Mercury, Venus, Earth and Mars. Three Major Characteristics of the Inner Planets Terrestrial Planet Formation. Mercury is the smallest terrestrial planet in the solar system, about a third the size of Earth. The inner planets formed about 4.5 billion years ago as huge, hot balls of solids and gases. So the inner solar system objects are made of iron, silicon, magnesium, sulfer, aluminum, calcium and nickel. At the center of the solar system is the Sun. Like the Earth, terrestrial planets have a core of iron and rock. On the other hand, the outer planets are said to be made of gases and they are not really solid. The inner planets are made up of rock and metal and are therefore solid. They have an average diameter of about 13000 km as they are small planets. This phenomenon is due to the beginning of the formation of the solar system. read more The size and composition of the planets is caused by the density of the elements that make up the planets. Venus’ core is believed to be iron-nickel, similarly to Earth. All of the rocky inner planets, as well as the moon, have an iron-dominant core. The Solar Wind,... Presenting: The Inner Planets. Venus and Mars have an additional major element in the core. As of 2014, Earth is the only terrestrial planet known to have life. Inner planets posses some characteristics which are unique to them. 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