Formation of the Solar System: The Solar Nebular Theory

1. Formation of the Solar System: The Solar Nebular Theory Video

2. Objectives • Explain the nebular hypothesis of the origin of the solar system • Express the sequence of events that led to the formation of our solar system • Describe how the planets formed

3. The Basics • Solar System: the sun and other celestial objects gravitationally bound to it • eight planets • three dwarf planets (Pluto, Ceres, Eris) • 165 known moons • Planet: any body in orbit around the Sun which • has enough mass to form itself into a spherical shape and • has cleared its immediate neighborhood of all smaller objects. • There are eight known planets in our solar system which meet this qualification: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune.

4. A Bit of History • Scientists have long debated the origins of the solar system. • In the 1600s and 1700s, many scientists thought the sun formed first and produced materials which later formed the planets. This was incorrect. • In 1796, French mathematician Pierre Simon, advanced a hypothesis now known as the nebular hypothesis. • Ummm yeah, what the heck is a nebular? • A cloud is called nebula - so a nebular hypothesis is like a “cloud” hypothesis • The piece of cloud which formed our own solar system is called the solar nebula

5. The Nebular Hypothesis • About 4.6 billion years ago ice, gas, and dust (nebula/cloud) collapsed under the weight of its own gravity, began to rotate, and eventually formed our solar system • The gases present were primarily hydrogen and helium

6. The temperature increased as the nebula collapsed Rotation increased with temperature Nebula eventually flattened into a disk As the sun was forming in the center of the nebula, dust particles in the outer regions combined to form planetesimals a few km across The Nebular Hypothesis

7. Formation of Planets • Planetesimal: a small body from which a planet originated • Eventually, the planetesimals formed into larger bodies called protoplanets through accretion… • Accretion is growing by colliding and sticking • Protoplanets’ gravity attracted other planetesimals, which added to their masses • Eventually, they became very large and formed planets and moons.

8. Evidence for Theory • The sun is composed of 99% of all matter which was contained in the solar nebula. • All planets orbit the Sun, and rotate in the same direction. This would be expected if they all formed from a disk of debris around the Sun. • The planets are all composed of elements similar to that of our Sun. • The planets are all in the same plane as the sun • Modern scientific calculations support this theory and help explain how the sun and planets formed from an original nebula of gas and dust.

9. Formation of the Planets The diagram below shows the formation of the Solar System..

10. The Solar System – Relative Sizes of the Planets

11. Planetary Distances • Mercury 0.4 AU • Venus 0.7 AU • Earth 1.0 AU • Mars 1.5 AU • Jupiter 5.0 AU • Saturn 10.0 AU • Uranus 19.0 AU • Neptune 30.0 AU • Pluto (planet?) 39.0 AU • Light travels through space at 300,000-km/s. • So it takes about 8 minutes for light from the sun to travel 1 AU and reach us. • How long would it take light from the sun to reach Pluto? • 39 x 8 = 312 minutes, or 5.2 hours!

12. Inner Planets Formation of Inner Planets • The features of a newly formed planet depended on the distance between it and the developing sun. • The four closest to the sun became Mercury, Venus, Earth, and Mars. • These are smaller, rockier, and denser than the outer planets. They contain large percentages of heavy elements, such as iron and nickel. • Lighter elements may have been blown away by radiation and the solar wind from the sun. Planetary gravity was not strong enough to retain their gases.

13. Outer Planets Formation of the Outer Planets • The next four planets are larger and became Jupiter, Saturn, Uranus, and Neptune. • These planets are referred to as Jovian or gas giants because they are composed primarily of hydrogen and helium. • Other characteristics include: low densities, rapid rotation, deep atmospheres, rings and lots of satellites.

14. Many scientists have declassified Pluto from planetary status. They do not believe it qualifies as a major planet. Pluto’s orbit is around our sun is different than the other nine planets, so astronomers have always suspected it may be not actually be a planet in our solar system. Recently, astronomers have discovered hundreds of objects similar to Pluto beyond Neptune’s orbit. None of these objects are larger than Pluto, but Pluto is probably one of these objects. Some scientists believe that Pluto once was one of Neptune’s moons, and that it pulled out away from Neptune and made its own orbit. Hey, What About Pluto?

15. Pluto, used to be the ninth planet from the Sun, and the smallest in our solar system. Pluto is the farthest planet from the sun. It is the smallest of known planets and is even smaller than Earth’s moon. Pluto is very cold and may be best described as an ice ball made of frozen gases and rocks. Just in Case Things Change

16. Ways We’ve Studied the Solar System • Space Shuttle • Space Missions • Voyager • Cassini • Galileo • Messenger • Pathfinder • Spirit and Opportunity • Deep Impact Rarely Seen Shuttle Activity NEAR Video Mars Phoenix Lander

17. Learning check How is Pluto different from the other outer planets?

18. Reading check How is Pluto different from the other outer planets? Unlike the other outer planets, Pluto is very small and is composed of rock and frozen gas, instead of thick layers of gases.

19. Nebular Hypothesis Homework • On a blank sheet of paper, write your name, date, and period in the upper right hand corner • On the top half of the page, sketch a series of diagrams showing the nebular hypothesis (look at pages 686-687 of the book for help) • On the bottom half, write a paragraph describing what happened during the nebular hypothesis (use the textbook and your notes for help) • Due Tomorrow…Friday 1/18/2013