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The Planets. Sizes and Distances. Planets can be seen because they reflect sunlight – they do not give off visible light of their own Astronomical Unit (AU ) – Earth’s average distance from the Sun The planets are spaced unevenly. Sizes and Distances.
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Sizes and Distances • Planets can be seen because they reflect sunlight – they do not give off visible light of their own • Astronomical Unit (AU) – Earth’s average distance from the Sun • The planets are spaced unevenly
Sizes and Distances • Inner Solar System – planets that are smaller, relatively close together and close to the Sun (Mercury, Venus, Earth, Mars)
Sizes and Distances • Outer Solar System – planets are larger, farther from the Sun, and much more spread out (Jupiter, Saturn, Uranus, Neptune)
Orbits • More than 99% of all the mass in the solar system is in the Sun • The gravitational pull of this huge mass causes planets and most other objects in the solar system to move around, or orbit, the Sun • Ellipse – the shape of each orbit – a flattened circle or oval
Formation of the Solar System • The planets orbit the Sun in similar ways – their paths are almost in a flatplane • The planets and other objects orbit the Sun in the same counterclockwise direction, giving scientists clues about how the solar system formed
Formation of the Solar System • The solar system formed out of a huge cloud of different gases and specks of dust, which flattened out into a disk of whirling material - most of the mass fell to the center and became a star, the Sun
Formation of the Solar System • Large Round Objects • When an object has enough mass, gravity pulls each part together in towards the center to make the object round • The planets formed when tiny bits of dust and frozen gases in the disk stuck together in clumps and the clumps continued to stick together
Formation of the Solar System • Small Lumpy Objects • Small rocky clumps close to the Sun are called asteroids • Small icy clumps farther from the Sun are called comets
The Terrestrial Planets • Terrestrial Planets – the four planets closest to the Sun (Mercury, Venus, Earth, Mars) • All terrestrial planets have layers – rocky crusts and dense mantles and cores • Atmospheres on terrestrial planets mainly formed from gases that poured out of volcanoes
The Terrestrial Planets • Four types of processes then shaped each planet’s rocky crust • Tectonics– the processes of change in a crust due to the motion of hot material underneath • Volcanism– when molten rock moves from a planet’s hot interior onto its surface
The Terrestrial Planets • Weathering and Erosion - weather or small impacts break down rocks and the broken material is moved by a group of processes called erosion • Impact Craters - a small object sometimes hits a planet’s surface so fast that it causes an explosion – the resulting impact crater is often ten times larger than the object that produced it
The Gas Giants • Gas Giants – are made mainly of hydrogen, helium, and other gases (Jupiter, Saturn, Uranus, and Neptune) • The huge gravitational force from such a large mass is enough to pull the gas particles close together and make the atmosphere very dense
The Gas Giants • There are strong winds and other weatherpatterns • Scientists think that each of the four gas giants has a solid core, larger than Earth, deep in its center
Video • Alien Planets Revealed- http://video.pbs.org/video/2365149642/