Components of the Solar System: The Sun, Planets, Satellites, Asteroids, and Comets

1. Chapter 7 The Solar System

2. Components of the Solar System

3. The Sun • The Sun is a star, a ball of incandescent gas whose light and heat are generated by nuclear reactions in the core. It’s mass is more than 700 times the mass of everything else in the solar system put together.

4. The Sun-2 The Sun’s gravitational force holds the planets other bodies in the solar system in their orbital patterns. The Sun is mostly hydrogen, 71%, and helium, 27%. It also contains very small proportions of all of the other elements.

5. The Planets • The planets are much smaller than the Sun and orbit around it. • They emit no visible light of their own but shine by reflected sunlight, a property known as albedo. • The planets move around the Sun in approximately circular orbits, all lying on nearly the same plane.

7. The Planets-2 • The Solar System is like a spinning disc with the planets traveling around the sun in the same counterclockwise direction. • Because of this, the planets appear to lie in a line in the sky. • As the planets orbit the Sun, each spins on its rotation axis. • The spin is generally in the same direction.

8. The Planets-3 • The tilt of the rotational axes relative to the planetary orbit is not far from perpendicular. • There are 2 exceptions, Venus and Uranus. Their tilts are extremely large. • The flattened structure and the orderly orbital and spin properties of the Solar System are 2 of its most fundamental features and any theory of the Solar System must explain them. • A third, but equally important feature is that the planets fall into 2 families called inner and outer planets.

10. The Planets-4 • The inner and outer planets are classified based on their size, composition and location in the Solar System.

12. Inner Planets Mercury Venus Earth Mars Outer Planets Jupiter Saturn Uranus Neptune Two Types of Planets

13. Two Types of Planets-2 • The inner planets are small rocky bodies with relatively thin or no atmospheres. • The outer planets are gaseous, liquid or icy. They have deep, hydrogen-rich atmospheres. • The term “rocky” for the inner planets means material composed of silicon and oxygen (SiO2-sand) with a mixture of other elements such Al, Mg, S and Fe.

14. Two Types of Planets-3 • By ice, we mean frozen liquids and gases, not just frozen water. • This would include CO2, NH3, CH4 etc. • Rock is rare in the Solar System by percentage because of the abundance of Hydrogen compared to Silicon. • The inner part of the system is mostly rock because of the heat of the sun.

15. Two Types of Planets-4 • The gases and liquids cannot condense to mix with the Silicon in the heat. • The outer planets generally have no true surface. • The atmospheres of the outer planets thicken with depth and eventually liquefy. • There is no distinct boundary between atmosphere and crust.

16. Two Types of Planets-5 • Deep in the interior, the liquid may compress enough to form a solid. • The transition from liquid to solid is no sharply defined. • We probably will never land on Jupiter, we would simply sink deeper and deeper into its interior.

17. Two Types of Planets-6 • The inner planets are sometimes referred to as the “Terrestrial” or Earth-like planets. • The outer planets are sometimes referred to as the “Jovian” or Jupiter-like planets.

19. Satellites • Many of the planets have satellites themselves. • Only Mercury and Venus do not have moons. • The moons usually move in a roughly circular path around the equator of the planet. • Only the moons of Uranus and Pluto are not near the equatorial plane, an important clue to the origin of the moons. • Jupiter, Saturn and Neptune have large families of moons, 62,31 and 27 respectively.

20. Asteroids and Comets • Asteroids and comets are much smaller than planetary bodies. • Asteroids are rocky or metallic bodies with diameters that range from a few meters up to about 1000 km. • Comets are icy bodies about 10 km or less in diameter. • Comets grow huge tails of gas and dust as they approach the sun.

21. Asteroids and Comets-2 • The comets are partially vaporized by the flow of energy from the sun. • Their composition puts them into 2 families, much the same as the planets. • Asteroids and comets also differ in their location within the Solar System. • Most asteroids are found in a large gap between Mars and Jupiter called the “asteroid belt”.

22. Asteroids and Comets-3 • It may be material that failed to aggregate into a planet as a result of disturbance by the gravity of Jupiter. • Most comets are found in an orbit far beyond Pluto in an area called the Oort cloud. • It is named after the Dutch Astronomer who proposed its existence.

23. Asteroids and Comets-4 • It completely surrounds the Solar System in a spherical region 40,000 to 100,000 astronomical units from the sun. • Even though most comets originate in the Oort cloud, some may come from a disk-like swarm of icy objects that lies just beyond the orbit of Neptune and extends to about 60 au from the Sun. • This area is called the “Kuiper Belt”. • Together the cloud and belt may hold 1012 comet nuclei.

25. Composition Differences • Astronomers can deduce a planet’s composition in several ways. • From the planet’s spectrum we can measure its atmospheric composition and get some information about the nature of its surface rocks. • The spectrum does not give a clue about internal composition.

26. Composition Differences-2 • Earthquake waves could give us information, but to date we do not have any working detectors on the inner planets. • The outer planets provide a different problem because of the lack of surface. • Density is another way to give us an idea of composition.

27. Density as a Measure of a Planet’s Composition • By using Newton’s modification of Kepler’s 3rd law, we can determine the mass of the planet by observing the effect of the mass of the planet has on an orbiting body such as a moon. • Volume can be determined by measuring the planets radius. • (V=4πR3/3; R is the planets radius)

28. Density as a Measure of a Planet’s Composition-2 • Radius can be measured by angular size and distance. • With both mass and volume, we can determine density of the planet. (D=M/V) • Once the planet’s average density is known, we can compare it with the density of abundant candidate materials. • Earth has a density of about 5.5, about intermediate between silicate rock (3 g/cm3) and iron (7.8 g/cm3).

29. Density as a Measure of a Planet’s Composition-3 • Because of this data, we can deduce that the Earth has a silicate rock surface with and iron core. • This has also been confirmed using earthquake information. • Density comparison is a powerful tool to use to study planetary composition, but it also has drawbacks.

30. Density as a Measure of a Planet’s Composition-4 • There may be similar substances that might match the given density. • The density of a material can be affected by a planet’s gravitational force. • A massive planet may crush rock whose normal density is 3 to a density of 7 or 8. • All of the terrestrial planets have a density similar to that of the Earth (3.9-5.5).

31. Density as a Measure of a Planet’s Composition-5 • The jovian planets have a density that is much smaller (0.71-1.67), about that of ice. • After correcting for gravitational compression, we can conclude that all of the inner planets contain large amounts of rock and iron and that the iron has sunk to the core.

32. Density as a Measure of a Planet’s Composition-6 • The outer planets contain mainly light materials such as hydrogen, helium, methane, ammonia and water. • The outer planets probably have core of iron about the size of the Earth, beneath their deep atmosphere. • Astronomers deduce the existence of the cores in 2 ways.

33. Density as a Measure of a Planet’s Composition-7 • If the outer planets have the same relative amounts of heavy elements as the Sun, they should contain several Earth masses of iron and silicates. • Because they are much more dense than the gases that make up the majority of the planet’s mass, they sink to form the core. • Analysis of rotational data shows that the equatorial bulges can best be explained if they have small dense core.

34. Density as a Measure of a Planet’s Composition-8 • Composition studies show the differences between families but also furnishes astronomers with another clue to the origin of the planets. • The Sun and the planets were made from the same material. • Because Jupiter and Saturn have a composition nearly identical to the Sun, and the inner planets have a similar composition if you remove the hydrogen and helium component, we can conclude that the process must keep the inner planets from capturing the light gases.

35. Bode’s Law

36. Bode’s Law • Bode’s Law is a curious relationship, that is stilled unexplained. • The gap in the prediction corresponds nicely with the location of the asteroid Ceres, first discovered by Giuseppi Piazzi. • Verification of Bodes Law will come when we can establish the same relationship in other solar systems.

37. Age of the Solar System • In spite of the differences in size, structure and composition, the planets, asteroids and comets all seem to have formed at nearly the same time. • We can directly measure the Earth, Moon and some asteroids from the radioactivity of their rocks (about 4.6 billion years old). • The Sun’s age is similar based on it’s current brightness and it’s presumed rate nuclear fuel consumption.

38. Origin of the Solar System

39. Origin of the Solar System • Observations that have to be accounted for when formulating a theory about the origin of the solar system. • The Solar System is flat, with all of the planets orbiting in the same direction. • There are 2 types of planets, inner and outer, with the rocky ones near the Sun and the gaseous or liquid ones farther out.

40. Origin of the Solar System-2 • The composition of the outer planets is similar to the Sun’s while that of the inner planets is like the Sun’s minus the gases that condense only at low temperatures. • All of the bodies in the Solar System whose ages have so far been determined to be 4.6 billion years old.

41. Origin of the Solar System-3 • Other details that could also be explained are structure of asteroids, number of craters on planetary and satellite surfaces as well as detailed chemical composition of surface rocks and atmosphere. • The currently favored theory for the origin of the Solar System derives from the theories proposed in the eighteenth century by Immanuel Kant and Pierre Simon LaPlace.

42. Origin of the Solar System-4 • They independently proposed the “Solar Nebula Hypothesis”. • The Solar System originated from a rotating flat disk of gas and dust, with the outer part of the disk becoming the planets and the center becoming the Sun. • This theory offers a natural explanation for the flattened shape of the system and the common direction of motion of planets around the Sun.

43. Interstellar Clouds • Interstellar clouds are the raw material of the Solar System. • The clouds are found in many sizes and shapes . • The one that formed the Solar System was probably a few light years in diameter and contained about twice the present mass of the Sun.

44. Interstellar Clouds-2 • If the cloud was typical of today’s clouds, it contained about 71% hydrogen and 27% helium with tiny traces of other elements such as carbon, oxygen and silicon. • In addition to the gases, interstellar clouds also contain tiny dust particles called interstellar grains.

45. Interstellar Clouds-3 • Interstellar grains range in size from large molecules to micrometers or larger. • They are believed to be made of a mixture of silicates, iron compounds, carbon compounds and water frozen into ice. • This is determined by analyzing the spectrum of light that passes through the cloud.

46. Interstellar Clouds-4 • The cloud began its transformation into the Sun and planets when the gravitational attraction between the particles in the densest part of the cloud caused it to collapse inward. • The collapse may have been triggered by a star exploding nearby or by a collision with another cloud.

47. Interstellar Clouds-5 • The infall was not directly to the center. • Because the cloud was rotating, it flattened. • Flattening occurred because rotation retarded the collapse perpendicular to the rotation. • A similar effect occurs when pizza dough is flattened by tossing it into the air with a spin.

48. Formation of the Solar Nebula • It probably took a few million years for the cloud to collapse and to become the rotating disk with a bulge in the center. • The disk is called a solar nebula. • The disk eventually condensed into the planets and the bulge into the Sun. • This helps to explain the property of the solar system with the planets on the same plane.

49. Formation of the Solar Nebula-2 • The solar nebula was probably about 200 AU in diameter and 10 AU thick. • These measurements seem consistent with stars and disks around them. • The stars in the center are not yet hot enough to emit visible light

50. Condensation of the Solar Nebula • Condensation occurs when a gas cools and its molecules begin to stick together to form liquid or solid particles. • The gas must cool below a critical temperature. • If we cool a cloud of vaporized iron (2000 K) to 1300 K, tiny flakes of iron will condense from it.