According to this model, the planets initially formed as cold spheres resulting from slow accumulating of dust and gas.Ĥ. In the early 20th Century, scientists generally discounted the idea of condensation of planets directly from a hot gas cloud and instead favored the hypothesis that the planets and other solar system bodies aggregated from cold clouds of dust and gases. Another early theory called for condensation (solidification) of the planets from a hot, gaseous cloud called the solar nebula rather than having the planets derived from the sun itself.ģ. Thus according to Buffon, the sun was much older than the planets.Ģ. This material later cooled and condensed to form the planets. He proposed that the gravitational attraction of passing comets had pulled hot, gaseous material from the sun. During the late 1700s, Buffon envisioned the planets as having formed from the sun. Theories on the Origin of the Solar Systemġ. Most Jovian Planets have impressive ring systems composed of dust- to boulder-sized particles of mostly ice. Most Jovian Planets have multiple moons.Ħ. Pluto lacks a thick atmosphere and instead consists of a solid core with a thick outer layer of ice.ĥ. Each (except for Pluto) consist of a solid core (probably rocky) surrounded by a thick atmosphere composed of methane, ammonia, hydrogen, helium and other gases. Generally larger then the terrestrial planets.Ĥ. Occur beyond the orbit of Mars and consist of Jupiter, Saturn, Uranus, Neptune and Pluto.Ģ. This tells us that the these rocky planets formed more or less from similar material early in the history of the solar system.ġ. Differences observed among the rocky planets reflect factors such as size and distance from the Sun rather than composition. Volcanism is largely basaltic, a black rock relatively rich in Mg, Si, O and Ca.Ħ. Composed mainly of silicates in addition to Fe and Ni.ĥ. Are generally small, rocky bodies sharing many similarities and also differences.Ĥ. Closest to the sun and consist of Mercury, Venus, Earth and Mars.Ģ. The rotations of planets, moons and other bodies are inherited from the rotation of the ancient gas cloud from which they formed.ġ. Meteoroids, asteroids and comets also follow orbits around the sun.Ħ. Most of the moons revolve around the planets in the same direction as the planets revolve around the sun.ĥ. The planets generally revolve in the same direction around the sun and within the plane of the ecliptic except for Pluto, which is tilted at 17 o to the ecliptic.Ĥ. The orbits of the planets are elliptical around the sunģ. Figure 1.3: The Solar System consists of the Sun, nine planets, 61 moons and a multitude of asteroids, comets and meteoroids.Ģ. CHAPTER 1: ORIGIN OF THE PLANETS & THE SOLAR SYSTEM TODAYġ.
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