3 The Planets: An Overview Terrestrial Planet – any of the Earth-like planets: Mercury, Venus, Earth, and MarsJovian Planet – the Jupiter-like planets: Jupiter, Saturn, Uranus, and Neptune; these planets have relatively low densities and are huge gas giantsSize is the most obvious difference between the terrestrial and the Jovian planetsThe diameter of the largest terrestrial planet, Earth, is only ¼ the diameter of the smallest Jovian planet, Neptune; it’s mass is only 1/17 that of NeptuneDensity, chemical makeup, and rate of rotation are other ways in which the two groups of planets differThe densities of the terrestrial planets average about 5 times that of water, while the Jovian planets only average about 1.5 times that of water
6 The Interiors of the Planets The substances that make up the planets are divided into 3 groups: gases, rocks, and icesGases – Hydrogen and Helium (melting point = -273oC)Rocks – Silicate minerals and metallic iron (melting point = 700oC)Ices – Ammonia, methane, carbon dioxide, and water (melting point = 0oC)Terrestrial planets contain mostly rock material, while the Jovian planets contain the gases and ices.
8 The Atmospheres of the Planets A planet’s ability to retain an atmosphere depends on its mass and sizeJovian planets have thick atmospheres of hydrogen, helium, methane, and ammonia, due to their high surface gravities and the ability to hold on to the light gasesTerrestrial planets have very small atmospheres in comparison, with the atmosphere making up only a small portion of the planet’s mass
10 Formation of the Solar System – Nebular Theory Nebula – a cloud of dust and gas in spaceThese thin gaseous clouds begin to rotate and contract, and then spin fasterAccording to the nebular theory, the sun and planets formed from a rotating disk of dust and gasesAs the speed of rotation increased, the center of the disk began to flatten outThe matter became more concentrated in the center, eventually igniting a nuclear reaction (the sun)
11 Formation of the Solar System – Planetesimals Planetesimals – small, irregularly shaped bodies; formed from the collision of matter in spaceAs the collisions continued, the planetesimals grew larger, and began exerting their own gravityIn the inner solar system, it was so hot that only the metals and silicate materials could formIn the outer solar system, it was cool enough for the planets to attract ice and gases to add to their mass