1. Inner Planets (Part I) 1)Science 2)Intro to Inner Planets 3)Four Main Processes 4)Planetary Comparisons 5)Intro to Atmospheres Sept. 16, 2002

2. Announcements If you are not here today due to Yom Kippur, there will be an opportunity to make up today’s quiz after class on Weds. An extra credit problem will be available on the course web site tonight or tomorrow morning. It is due Thurs. Sep 19 at 5pm

3. Review Pieces of the Solar System Sun (in a few weeks) inner planets (this week) outer planets (next week) other stuff (following week) Angular momentum angular momentum is conserved Solar System formation accretion disk, rotation, protostar planetesimals solar wind

4. Fact vs. Theory Facts are data which has been measured e.g. the Sun rose this morning Theory is a model which describes/explains data or predicts future events e.g. the Sun will set tonight a thrown baseball will follow an arc because of gravity and Newton’s Laws the Earth revolves around the Sun and will continue to do so It is impossible to prove a theory even Newton’s Laws are a theory It IS possible to disprove a theory when facts do not agree with the model

5. Examples Fact: All major (currently observed) planets/moons/asteroids are revolving around the Earth in the same direction and in a similar plane Theory: The Solar System was created from a revolving sphere of gas and dust Facts: The inner planets are composed primarily from refractory materials while the outer planets are mostly volatile materials Theory: The inner region was hotter and the volatile materials did not survive there, but did in the outer region, this contributed to the planets’ formations

6. NASA Solar System Missions Flyby missions - satellite to pass by another object quick look, but cheap examples: Voyager, Mariner, Pioneer, … Orbiters - satellite in orbit around a planet or moon more detailed studies, but not “hands-on” examples: Galileo, Clementine, Magellan, … Landers - lander on the surface of a planet or moon get rock samples and direct data, limited area can be covered examples: Viking, Mars Surveyor, Mars Odyssey, … Manned missions - humans on the surface of a planet or moon can do advanced, complicated studies/experiments, but very expensive examples: Apollo 11 through Apollo 17

7. Differentiation During planetary formation, the rocks and planetesimals compress together due to gravity energy is converted into heat material melts and becomes fluid Differentiation is the process of the heavier materials sinking towards the center of the planet while lighter materials rise to the outer edges materials become separated by type Outer surface of planet cools fastest and hardens

8. Planet Interiors Layered solid inner core liquid outer core solid outer mantle/crust Hotter inside, cooler outside planet radiates heat into space outer crust cooled and hardened center is hottest and has highest pressure Melting point depends on temperature and pressure in the center, pressure wins and material is solid farther out, temperature wins and material is liquid outer edge, both lose and material is solid

9. Planet Interiors (cont) The inner planets have similar structure although we don’t have a lot of data on other planets Data on Earth’s interior comes from seismic readings of earthquakes

10. Four Main Processes  These processes shape the surfaces of planets 1)Tectonism  movement of pieces of the planet’s crust (plates) 2)Volcanism  flow of material (lava) from beneath the planet’s crust 3)Impact Cratering  meteors hitting a planet’s surface 4)Gradation  erosion of the surface  The first 3 processes build up structure on the surface (mountains, valleys, etc)  The last process wears the surface down

11. Tectonics Major movements of the planets crust create mountain ranges, deep valleys on Earth: tectonic plates rub against each other other planets: not plates, but major cracking/shifting (fractures)

12. Interior Heating Radiative cooling alone should have cooled the Earth’s interior more than observed Friction adds some of the heat tidal forces due to the gravitational pull of the Moon and Sun cause pieces of the interior to rub together this rubbing generates heat (just like rubbing your hands together) Radioactive decays add most of the heat The interior temperature is a balance between original heat, radiative cooling and additional heat As the radioactive material disappears, the Earth’s interior will cool

13. Volcanism Fissures in the planet’s crust can allow hot mantle to flow to the top (lava) the mantle is solid, but after relieving the pressure from the crust, it can turn liquid Long fissures cause shield volcanoes (large, long mounds of cooled lava) to form over long time periods Local “holes” can form mounds on Earth, plate movement limits the size and can result in a chain of islands Large flows of more fluid lava can create great plains of lava e.g. Lunar mares (seas) Amount of volcanic activity indicates how active a planet is

14. Comparative Volcanism Moon mares are volcanic in nature and indicate the Moon once had a lot of lava flow Mercury some visual indications of lava flow, not enough known Mars largest mountains in the Solar System (up to 25 km high) caused by volcanism Venus evidence of a lot of complex volcanic activity Earth lots of current and previous volcanic activity (Pompeii, Hawaiian Islands, Mt. St. Helen’s)

15. Impact Cratering The number of collisions between objects depends on how many objects there are Early in the Solar System there were many more small planetesimals: more collisions Number of craters can be used to “date” a planet Craters can be erased by tectonism, volcanism and gradation occurs on “active” planets (e.g. Earth) on “dead” planets, craters remain (e.g. Moon) Formation: heats and compresses material thrown outward surface rebounds

16. Comparative Cratering Moon lots of craters in all sizes Mars craters with impact craters which indicate there might have been water on Mars once Venus dense atmosphere protects Venus Earth protected by atmosphere (many meteors burn up) large oceans leave no impact crater most craters erased by gradation

17. Moon from the Earth Theory: the Moon comes from the Earth Mars size protoplanet hit Earth early in its history this impact showered large amounts of material into Earth orbit volatile materials were lost remaining materials condensed to form the Moon Facts which are explained: Moon composed of same materials as Earth (moon rocks) Moon has no significant volatile materials (water, air) Moon is large fraction of Earth’s size

18. Surface leveling caused by blowing wind, flowing water and water/ice freezing/melting Moon & Mercury no atmosphere, possible ice, little gradation Mars large dust storms observed, evidence of water flow Venus evidence of blowing wind, no evidence of water Earth all processes present e.g. dust/wind storms, rain, tides, glacier flow Gradation

19. Magnetic field Inner planets all have some magnetic field This magnetic field is not caused only by magnetized materials At least partially caused by rotation of Earth spinning electric charges in core create magnetic field Facts: Earth has a strong magnetic field Earth’s magnetic field moves with time (magnetic north pole not the same as celestial north pole) the Moon has no or very small magnetic field Mercury has strong magnetic field Venus and Mars have small magnetic field

20. Gases – Some Basics Lighter gases rise This is really because heavier gases sink and push the lighter gases upward Temperature of a gas is really the speed of the molecules Faster gases are hotter Sunlight and heat from a planet’s interior provide energy to heat atmospheres Sunlight can also break up molecules Fast atoms/molecules in the outer atmosphere can escape the planet’s gravitational pull Planets have a hard time hanging onto hydrogen and helium

21. Primary Atmosphere A planet’s original atmosphere comes from the gas of the accretion disk It is composed mainly of hydrogen and helium same stuff the Sun is made of If a planet’s gravity isn’t strong enough, it can’t hold onto these light gases They escape and leave the planet without an atmosphere Heating and solar wind help these processes This happened to the inner planets We will see later it did not happen to the gas giants