The Solar System

1. The Solar System

2. How did the solar system form? • The nebular theory (or accretion hypothesis) is the most widely accepted explanation. • NEBULAR THEORY • A nebula is an extremely large cloud of dust and gas. • The nebula is unstable, and begins to collapse around different regions because of an unequal distribution of matter.

3. Nebular Theory • As the nebula collapses around different areas of high mass, the gravitational attraction of these regions grows, which attracts more and more material. • These points where the matter collects become stars. • For this reason, nebulae are often called stellar nurseries.

4. Nebular Theory • As matter collects unevenly around the center, it begins the whole mass spinning. (PROTOPLANETARY DISK) • Most of the mass (99%) collects in the center forming the Sun. • The rest of the mass (1%) flattens into a spinning disk of dust and gas around the Sun.

5. Nebular Theory • Within the disk, areas of higher mass attract more and more material (accretion). • This accretion forms “planetessimals”, or the beginnings of planets.

6. Nebular Theory • When accretion is finished, we are left with our solar system.

7. The Sun • The Sun is the star at the center of our solar system. • Made mostly of hydrogen (92.1%) and helium (7.8%) • Nuclear fusion produces the Sun’s energy • About 1.3 million Earth’s could fit inside the Sun • 1.4 million km in diameter (109 times larger than Earth) • 5500 °C (9900 °F)

8. Gravity • Law of Universal Gravitation • All objects with mass exert a gravitational force on the objects around them. • Strength of force depends on the masses of the objects and the distance between them. • Because of the Sun’s great mass, all other objects in the solar system orbit around it.

9. Planets • A planet: • Orbits the Sun • Has a spherical shape • Is significantly more massive than the objects around it • There are 8 planets in our solar system • Inner planets • Outer planets

10. Inner Planets • The four planets closest to the sun (inside the asteroid belt) • Mercury, Venus, Earth, Mars • Smaller size (than the outer planets) • Rocky (Terrestrial) • Mostly iron core • Solid outer crust

11. Outer Planets • The four planets farthest from the Sun (outside the asteroid belt) • Jupiter, Saturn, Uranus, Neptune • Larger size (than the inner planets) • Called “gas giants” • Ice and gasses

12. Dwarf Planets • Like a planet… • Made of rock and ice • Spherical shape • Orbits the Sun • But not a planet! • Orbits near other similarly sized objects.

13. Asteroids • Small, rocky objects that orbit the Sun • Millions found in the asteroid belt between the orbits of Mars and Jupiter • Between one meter and several hundred thousand meters in length • Usually not spherical

14. Comets • Relatively small ball of gas, dust, and ice • Orbits the Sun • Usually an extremely elliptical orbit • Come from outer parts of the solar system • Sometimes called a “shooting star” • NOT A STAR!!!

15. Measuring Distances • Because of the great distances between objects in our solar system, we use a larger than usual measurement… • AU – Astronomical Unit • The average distance between Earth and the Sun • 150 million kilometers (150,000,000 km)

16. Geocentric Model? • It was once believed that Earth was the center of the universe and all other objects revolved around it. • Geo = Earth • Centric = Center

17. Heliocentric Model • Helio = Sun • Centric = Center • In the 1500’s, Copernicus proposed that Earth and other planets revolve around the Sun • Though the Sun was later observed NOT to be the center of the universe! • Supported by evidence collected as technology allowed further investigation.

18. Planetary Orbits • Kepler discovered that planetary orbits are elliptical rather than circular • Planets move faster when they are closer to the Sun, and slower when they are farther from the Sun. • Sun at one focus.