2 So, what is the solar system? The solar system includes the sun and the bodies revolving around the sun.
3 The debate Scientists have long debated the origins of the solar system. In the 1600s and 1700s, scientists that the sun formed first and threw off the materials that later formed the planets.
4 What are planets? Before August 2006, there was not a scientifically approved definition of a planet. One definition said that planets were the nine major bodies orbiting the sun.
5 New Definition… The IAU adopted the following definition of a planet on August 24, 2006: –"a celestial body that (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape and (c) has cleared the neighborhood around its orbit."
7 Marquis Pierre Simon de Laplace Who was he? –A French mathematician Why was he important? –He advanced the hypothesis that became the nebular theory. The what?
8 What is the nebular theory? De Laplace’s hypothesis stated that the sun and planets condensed out of the same spinning nebula.
9 What is a nebula? A nebula is a cloud of gas and dust.
10 The rest of the hypothesis… He went on to tell us that the entire solar system formed at approximately the same time. This hypothesis developed into what we now know as the Nebular theory.
11 The big bang spread matter throughout the expanding universe. Some of this matter gathered into clouds of dust and gas.
12 The clouds of gas and dust that became our solar system was the solar nebula. The solar nebula was larger than our solar system is now.
13 4 to 5 billion years ago, shock waves from a nearby supernova or some other force caused a cloud of dust and gas to contract, forming the solar nebula. The sun began to form in the center of the solar nebula.
14 About 99 percent of the matter in the solar nebula became part of the sun.
15 The planets As the sun was forming, planets were forming in the outer regions of the solar nebula. The formation of the planets occurred in stages.
16 What are moons, anyway? We often hear them called satellites. The book defines them as the smaller bodies that orbit the planets.
18 Formation of planets The distance between a protoplanet and the developing sun influenced the composition of the planet that formed from the protoplanet.
19 The 4 protoplanets closest to the sun became Mercury, Venus, Earth and Mars. They contained large amounts of the heavier elements, such as iron.
20 The next four protoplanets became Jupiter, Saturn, Uranus, and Neptune. They formed in the cold regions of the solar nebula.
21 The material of these outer protoplanets was helium, hydrogen, and frozen gases such as water, methane, and ammonia.
22 They formed into huge planets due to their distance from the sun. We now refer to them as gas giants.
23 Pluto At the time that our book was written, Pluto was the farthest planet from the sun. It was also the smallest of the known planets. Pluto is best described as an ice ball of frozen gases and rock.
24 Dwarf Planets Pluto is now a dwarf planet. According to NASA, a dwarf planet: –(a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, (c) has not cleared the neighborhood around its orbit, and (d) is not a satellite.