Introduction to the Solar System

1. Introduction to the Solar System The bright star Antares embedded in dust and gases

2. The Formation of the Solar System • Through the course of history there have been many theories about the solar system • Early Greeks thought the Earth was the center of the solar system, with the stars, sun and moon revolving around the Earth – the Geocentric Model • In 1543, a scientist proposed that the sun was the center of the solar system and the planets revolved around it – the Heliocentric Model

3. Origin of the Solar System • Modern astronomers believe that the sun and planets condensed out of a nebula or large cloud of gas and dust. • This idea is named the Nebular Hypothesis. It was first presented by the German philosopher Immanuel Kant in the late 1700’s. • Such clouds have been observed around stars other than our sun (e.g., Beta Pictoris)

4. The Formation of the Solar System Our solar system began as a rotating gas cloud or nebula that collapsed toward its center under the influence of gravity. The condensing and contracting caused the cloud to begin to rotate, as it rotated the center became dense and the temperature reached about 10 million K A condensation formed at the center, which is called a protostar. The extremely high temperatures allowed for a process called nuclear fusion to occur A flattened disk of matter surrounded the protostar, which began to shine and become a star, our sun.

5. The Formation of our Solar System • The rising temperature from the sun removed the gas from the inner regions, leaving dust and larger debris • Inner planets formed from solid debris • Outer planets retained original gases Planets established dominance in their regions of the solar system. After almost all of the remaining gas, dust, and small debris was collected by the larger objects, the solar system took on the form we recognize today.

6. Other Star Systems Forming • We can look at young star systems developing today. • The planets orbiting these stars are formed from the surrounding disks of gas and dust, called protoplanetary disks or proplyds. Proplyd in the Orion Nebula

7. Mercury • Venus • Earth • Mars • Jupiter • Saturn • Uranus • Neptune Solar System Composite http://www2.jpl.nasa.gov/galileo/sepo/education/nav/ss2.gif

8. Common Properties of Planet Orbits in Our Solar System As viewed from above, all of the planets orbit the Sun in a counterclockwise direction. The planets orbit in nearly the same plane (ecliptic). All planets except Pluto have an orbital inclination of less than 7°.

9. Inner Solar System http://www.nineplanets.org/overview.html

10. Outer Solar System http://www.nineplanets.org/overview.html

11. Pluto’s orbit, or plane of revolution, is tilted by 17° to the general solar system orbits (ecliptic) Pluto can also cut across Neptune’s orbit (but they can never collide) Pluto’s Odd Orbit

12. Ecliptic Plane • Plane of the Ecliptic: The orbits of the planets are mostly in the same plane. • This plane is called the ecliptic and is defined by the plane of the earth’s orbit. • The exception is Pluto, which is tilted quite a bit in comparison to the rest of the planets. • The ecliptic plane is a remnant of the original, rotating nebular disk that formed the sun and planets

13. Ecliptic: Artist’s View

14. Motions • Directions of Motion: The planets orbit in a counterclockwise direction around the sun (when looking down upon the solar system from the sun’s north pole). • All the planets, except for Venus, Uranus, and Pluto, rotate in the same direction as their orbits.

15. Orbits • The planets nearest to the Sun (Mercury, Venus, Earth, and Mars) are relatively close together, while those farther away (Jupiter, Saturn, Uranus, and Neptune) are more spread out. • Most of the planets are in nearly circular orbits.

16. The astronomical unit (AU) is useful in measuring distances in the solar system One AU equals the average earth-to-sun distance of 93 million miles AU distances allow direct comparison to the earth which is equal to 1.0 Solar System Orbits (AU)

18. Mercury 88 days Venus 224.7 days Earth 365.25 days Mars 1.88 years Jupiter 11.86 years Saturn 29.5 years Uranus 84 years Neptune 164.79 years Pluto 248.32 years Revolutions of the Planets* *Earth days and years

20. Diameters

22. Masses

24. Average Density (kg/m3)

26. Rotational Period

28. Average Temperature

29. Average Temperature (Earth = 1)

30. In mass, the sun represent 99% of the solar system The smallest planet, Mercury, has a diameter of 3031 mi Pluto, the previous smallest planet, has a diameter of 1457 mi The largest planet, Jupiter, has a diameter of 88,700 mi Earth = 7926 mi Ganymede, the largest moon of Jupiter, is larger than Mercury, yet Ganymede is not considered a planet because it revolves around Jupiter Sizes of the Planets http://www.nineplanets.org/datamax.html

31. Two Basic Groups of Planets TERRESTRIAL (earth-like) Small size, low Mass Higher density Mostly rock Mercury, Venus, Earth, Mars JOVIAN (Jupiter-like) Large size, massive Low density Mostly gas Jupiter, Saturn, Uranus, Neptune

32. Classifications • Terrestrial or Rocky planets—Composed of rock and metal: Mercury, Venus, Earth, Mars • Jovian or Gas planets—Composed primarily of the gases hydrogen and helium: Jupiter, Saturn, Uranus, Neptune

33. Classification, cont. • Small Planets—Diameters less than 13,000 km: Mercury, Venus, Earth, Mars • Giant Planets (Gas Giants)—Diameters greater than 48,000 km: Jupiter, Saturn, Uranus, Neptune

34. Classification, cont. • Inner Planets—Mercury, Venus, Earth, Mars • Outer Planets—Jupiter, Saturn, Uranus, Neptune

35. Classification, cont. • Inferior—Closer to the sun than earth: Mercury and Venus • Superior—Farther from the sun than earth: Mars, Jupiter, Saturn, Uranus, Neptune

36. Classification, cont. • Classical—Known since prehistoric times, visible to the unaided eye: Mercury, Venus, Mars, Jupiter, Saturn • Modern—Discovered in modern times, visible only with telescopes: Uranus, Neptune, (Pluto)

37. Classification Table

38. Planets: Mercury Venus Earth Mars Ceres (dwarf) Jupiter Saturn Uranus Neptune Pluto (dwarf) Eris (dwarf) Makemake (dwarf) New Solar System (> 2006) Eris • Two Categories: Planets and Dwarf Planets (dwarfs beyond Neptune are “Plutoids”) • Today’s astronomers recognize only 8 planets

39. Solar System Model • If the sun were an orange, the earth would be a grain of sand thirty feet away. • Jupiter would be a cherry pit located one block from the sun. • Saturn would be another cherry pit located one block from Jupiter. • Pluto would be a grain of sand 10 blocks from the sun. • The nearest star to our sun (Alpha Centauri) would be represented as another orange 2000 miles from the sun.

40. Jupiter from Fantasia (Disney) Planet Names • The planets have been given the Roman names of gods from ancient Greece. Roman • Mercury, Venus, Mars, Jupiter, Saturn Greek • Hermes, Aphrodite, Ares, Zeus, Kronos The modern planets, Uranus, Neptune, and Pluto, are also Roman gods