Chapter 26: THE SOLAR SYSTEM

1. . Chapter 26: THE SOLAR SYSTEM

2. This lecture will help you understand: • The Solar System and Its Formation • The Sun • The Inner Planets • The Outer Planets • Earth’s Moon • Failed Planet Formation

3. The Solar System and Its Formation The solar system consists of: • Sun • System of planets • Asteroids • Comets

4. The Solar System and Its Formation Planets are divided into two classes: • Inner planets: Mercury Venus Earth Mars • Outer planets: Jupiter Saturn Uranus Neptune

5. The Solar System and Its Formation The Nebular theory: Theory that the Sun and planets formed together from a cloud of gas and dust—a nebula.

6. The Solar System and Its Formation Nebular theory formation: • Gravitation between materials in the cloud pulled it inward. • When pulled inward, spin increased in accord with the conservation of angular momentum. • The spinning cloud conformed to the shape of a spinning disk.

7. The Solar System and Its Formation • Nebular theory formation: • The center of the disk is the protosun. • Away from the center, planetesimals formed. • Planetesimals accreted more matter to become planets.

8. The Solar System and Its Formation CHECK YOUR NEIGHBOR Which of the following orbits around the Sun? A. Planets. • Comets. • Asteroids. • All of the above.

9. The Solar System and Its Formation CHECK YOUR ANSWER Which of the following orbits around the Sun? A. Planets. • Comets. • Asteroids. • All of the above.

10. The Solar System and Its Formation CHECK YOUR NEIGHBOR As a nebula shrinks under the influence of gravity, it A. spins slower. • spins faster. • loses its spin. • spins into a protosun.

11. The Solar System and Its Formation CHECK YOUR ANSWER As a nebula shrinks under the influence of gravity, it A. spins slower. • spins faster. • loses its spin. • spins into a protosun. Explanation: In accordance with the conservation of angular momentum, as the radius of the nebula decreases, its spin rate increases (like a skater who pulls her arms inward in a spin).

12. The Sun Sun: • nearest star to Earth • composed of mostly hydrogen in the plasma phase • hydrogen is fused to helium by thermonuclear fusion in its core • 4.5 million tons of mass are converted to energy each second • a tiny fraction of this energy reaches and sustains Earth

13. The Sun CHECK YOUR NEIGHBOR Strictly speaking, in every second that passes, the mass of the Sun A. decreases. • remains constant. • increases. • reinvents itself.

14. The Sun CHECK YOUR ANSWER Strictly speaking, in every second that passes, the mass of the Sun A. decreases. • remains constant. • increases. • reinvents itself. Explanation: It is this decrease that bathes the solar system with radiant energy. Solar mass is converted to energy via the celebrated equation, E = mc2.

15. The Inner Planets The inner planets—four nearest to the Sun composed of high-density solid rock: • Mercury • Venus • Earth • Mars Orbital speeds of planets around the Sun decrease with increasing distance from the Sun.

16. The Inner Planets Mercury: • closest to the Sun • slightly larger than our Moon • almost no atmosphere due to small size • daytime is long and hot (up to 430C) • nighttime is long and cold (about -170C)

17. The Inner Planets Venus: • next closest to the Sun • diameter about 0.95 that of Earth • very dense atmosphere, mostly carbon dioxide • volcanically active • very harsh place

18. The Inner Planets Earth: • third planet from the Sun—our home • at a distance where most of its water is neither solid nor gas, but liquid

19. The Inner Planets Mars: • fourth planet from the Sun—a potential away-from-home habitat • little more than half Earth’s size • thin atmosphere—95% carbon dioxide and 0.15% oxygen (A planet with a thin atmosphere is ineffective in reducing the temperature difference between day and night!) • equatorial temperatures range from 30C in day to –130C at night • presently the focus of planetary exploration

20. The Inner Planets Mars:

21. The Outer Planets Outer planets: • gaseous, low-density worlds • appreciably larger than Earth • more widely spaced than the inner planets • in order of distance from Sun— Jupiter Saturn Uranus Neptune

22. The Outer Planets Jupiter: • first of the outer planets, beyond Mars • more than 11 times Earth’s diameter—giant of the solar system • composition more liquid than gaseous or solid • atmospheric pressure more than a million times that of Earth’s

23. The Outer Planets Jupiter:

24. The Outer Planets Jupiter: • atmosphere is 82% hydrogen, 17% helium, 1% methane, ammonia, and other molecules— cough! • no definite surface as occurs on the inner rocky planets • solid core of iron, nickel, and other minerals Because of its thick atmospheric blanket, daytime and nighttime temperatures are about the same for equal altitudes above its “surface.”

25. The Outer Planets Jupiter’s four largest moons

26. The Outer Planets Jupiter’s moon Europa has an ice-capped ocean, which may hold extraterrestrial life

27. The Outer Planets Saturn: • most remarkable for its easily seen rings • twice as far from Earth as Jupiter • diameter about ten times that of Earth, excluding the rings • lowest density of all planets—could float in giant bathtub (density is less than that of water)

28. The Outer Planets Saturn: • surrounded by rings— hypothesized to be bits of a moon never formed, or remnants of a moon torn apart by tidal forces • inner part of rings, like any satellite, travels faster than outer part of the ring system Rocks that make up the rings orbit independently of other rocks.

29. The Outer Planets Saturn’s largest moon, Titan, was visited by the Cassini spacecraft.

30. The Outer Planets Uranus: • twice as far from Earth as Saturn is • diameter about four times thatof Earth • 98 tilt to the orbital plane—a most unusual feature • faint ring system • methane atmosphere • very cold place

31. The Outer Planets Neptune: • lies beyond Uranus • diameter almost four times that of Earth, somewhat smaller than Uranus • atmosphere mainly hydrogen and helium • highly elongated elliptical path about the Sun

32. The Outer Planets Pluto: • since 2006, classified as a dwarf planet • very unlike other planets in composition, size, and orbit • highly elliptical orbit, like comets • spends most of its orbital time well beyond Neptune, in the Kuiper Belt • composition like that of Kuiper-Belt objects • look-alike neighbors not classified as planets • former planetary status was more historical than astronomical

33. The Outer Planets CHECK YOUR NEIGHBOR Which planet is more dense than water? A. Mars. • Venus. • Neptune. • All of the above.

34. The Outer Planets CHECK YOUR ANSWER Which planet is more dense than water? A. Mars. • Venus. • Neptune. • All of the above. Comment: Saturn is the only planet with a density less than that of water.

35. Earth’s Moon Earth’s Moon: • more is known about the Moon than any other celestial body • diameter about one quarter that of Earth • no atmosphere—no weather and erosion to conceal past scarring of its surface (wears no “makeup”)\

36. Earth’s Moon Twelve people have stood on the Moon. Here we see Buzz Aldrin, one of the three Apollo 11 astronauts.

37. Earth’s Moon

38. Earth’s Moon Phases of the Moon:

39. Earth’s Moon The Moon spins about its polar axis as it revolves around Earth.

40. Earth’s Moon CHECK YOUR NEIGHBOR During the time of a new Moon, the A. Sun is between Earth and the Moon. • Moon is between the Sun and Earth. • Earth is between the Sun and the Moon. • None of the above.

41. Earth’s Moon CHECK YOUR ANSWER During the time of a new moon, the A. Sun is between Earth and the Moon. • Moon is between the Sun and Earth. • Earth is between the Sun and Moon. • None of the above. Explanation: A new Moon is mainly in the daytime sky, between Earth and the Sun. When it is exactly between them, we have a solar eclipse.

42. Earth’s Moon CHECK YOUR NEIGHBOR During the time of a full Moon, the A. Sun is between Earth and the Moon. • Moon is between the Sun and Earth. • Earth is between the Sun and the Moon. • None of the above.

43. Earth’s Moon CHECK YOUR ANSWER During the time of a full Moon, the A. Sun is between Earth and the Moon. • Moon is between the Sun and Earth. • Earth is between the Sun and the Moon. • None of the above. Explanation: A full Moon occurs when Earth is between the Sun and Moon, while in Earth’s view, the hemisphere of the Moon is fully in sunshine. When Earth is exactly between the Sun and the Moon, we have a lunar eclipse.

44. Earth’s Moon A magnetic compass aligns with a magnetic field. Like a compass in a magnetic field, theMoon aligns withEarth’s gravitationalfield.

45. Earth’s Moon Eclipses occur when the Moon’s shadow falls on part of Earth. This is a solar eclipse.

46. Earth’s Moon A lunar eclipse occurs when Earth’s shadow falls on the Moon.

47. Earth’s Moon Eclipse: The red light of sunrises and sunsets all around Earth is refracted onto the Moon’s surface during a lunar eclipse.

48. Failed Planet Formation Asteroids: • small rocky bodies that orbit the Sun • most are located between Mars and Jupiter • some encounter Earth • unnoticed on ground—conspicuous on ice (the reason many are found in Antarctica)

49. Failed Planet Formation Comets: • differ from asteroids in chemical composition • are masses of water, methane, and ice—dirty snowballs • most located in Kuiper Belt and Oort Cloud • highly elliptical (highly eccentric) orbital paths • tail of comets swept outward from Sun by solar wind

50. Failed Planet Formation