A Solar System is Born

1. Pgs 34 - 42 A Solar System is Born

2. What is our Solar System • Earth and the sun are the two major components of our solar system. • It includes all the other objects that travel around the sun. • Our book considers Pluto a planet. • In the study, of our solar system we will include Pluto since it does orbit the sun.

3. Solar Nebula • The requirements for making a planet are found in the seemingly empty space between stars. • The space actually contain a mixture of gas(hydrogen and helium) and dust (carbon and iron). • The gases and dust collect together in a cloud called a nebula. • Nebulas are cold and dark, but over time, interact with starlight to form new chemicals and molecules.

5. Gravity Pulls Matter Together • Nebulas contain gas and dust which have both matter and mass. • This means they are affected by gravity. • The denser a nebula gets, the stronger the gravitational pull it has on the molecules in it. • If gravitational pull is strong enough the cloud could collapse on itself, but there is another force that opposes this gravity.

6. Pressure Pushes Matter Apart • Temperature is a measure of how fast the particles of an object are moving. • If particles are moving slowly, the temperature is low and vice versa. • The particles in a cloud are always moving. • They even bump into each other creating pressure. • Pressure keeps the particles away from others and balances gravity.

7. The Solar Nebula Forms • Most of the time the particles of a nebula are balanced with gravity and pressure. • It can become unbalanced though. • Two nebulas can crash into each other or a nearby star can explode and its material can crash into a nebula. • When this happens gravity overcomes pressure and collapses the cloud inward. • When this happens, star and planet formation is possible. • This nebula is considered a solar nebula.

9. From Planetesimals to Planets • Once the solar nebula starts to collapse, matter in the cloud gets closer together. • The attraction between the particles became stronger and made the gas particles move faster and increased the temperature. • Gas and dust particles bump into each other until they rotate around the center of the cloud. • Eventually the nebula flattened into a rotating disk

10. Planetesimals • Some of the dust particles would stick together forming the building block of a planet called a planetesimals. • Planetesimals would grow over a few thousand years to the size of boulders. • Thousands of years later they would eventually grow to the size of planets.

12. Planets, Craters, and Comets • Once planets got large enough, their gravity was strong enough to attract nebula gases. • Closer to the sun, the gases would not stay attracted to the planets. • Pieces of debris from planetesimals became bigger and left many craters on the surface of rocky planets like Mercury, Mars and our moon. • In the final stage of planet formation, planetesimals crash on planets or get hurled into space. • Icy planetesimals will be seen as comets.

14. Birth of a Star • The center of the solar nebula became so massive and so hot that hydrogen fusion began. • The fusion created enough pressure to balance the gravity. • Gases stopped colliding and the sun was born. • Remaining gas and dust particles were blown into deep space. • The formation of the new solar system took about 10 million years. • How do we know? …. Telescopes looking at distant nebulas

16. Rotation and Revolution • The solar system is filling with moving bodies restricted to moving a certain way. • Rotation is the spinning of an object on its axis like the Earth. • Revolution is the moving around the sun on a path called an orbit. • The amount of time it takes for one revolution around the sun is the period of revolution.

17. Planetary Orbits • Why do planets continue to orbit the sun? • Why don’t they fly off into space? • Astronomer Tycho Brahe studied the planets for 25 years and recorded their movements carefully. • When he died his assistant Johannes Kepler inherited all the records and used them to create a set of laws that governs the motion of the planets.

18. Kepler’s First law of Motion • He found that Mars didn’t orbit in a circle, but an elongated circle called an ellipse. • An ellipse is a closed curve in which the sum of the distances from the edge of the curve of two point is always the same. • The maximum length of an ellipse is called the major axis. • Half of that distance is the semimajor axis. • Earth’s semimajor axis is 150 million km and is referred to as one astronomical unit (AU).

20. Kepler’s Second Law of Motion • Kepler discovered that planets move faster when they are closer to the sun. • Along the near side of the sun, a planet will actually move further during the same amount of time when it is farther away from the sun.

21. Kepler’s Third Law of Motion • Kepler discovered that the period of a planet’s revolution is related to its semimajor axis. • By knowing the period of a planet’s revolution you can calculate its distance from the sun. • Kepler’s Formula: p2 = a3 • P is the period of revolution. • A is the semimajor axis of an orbiting body.

22. Newton’s Law of Universal Gravitation • Sir Isaac Newton was the one who figured out why planets closer to the sun move quicker than planets that are farther away. • Newton saw that small objects fall toward the Earth because they are attracted to each other, but the small object appears to fall because it is much less massive.

23. Newton’s Law • The force of gravity depends on the product of the masses of the objects divided by the square of the distance between them. • F = G x (m1 x m2)/ (d1 – d2)2 • It states that if objects are twice as far apart, the gravitational force will be decreased by 4.

24. Newton’s Explanation • Newton’s explanation of the orbit of the moon and Earth made sense with an understanding of his laws of motion. • The moon doesn’t crash into the Earth. • It goes around continually. • Think of a ball attached to a string. • If you swing it around the ball goes around you until you let go of the string. • Gravity of planetary objects is similar.