Our Solar System

1. Our Solar System Chapter 29

2. Section 29.1 Overview of our solar system

3. Overview • Earth is one of eight planets revolving around or orbiting the sun • All of the planets, and their moons are called satellites • They all have various sizes, surface conditions, and internal structures

4. Early Ideas • Early astronomers assumed that the sun, planets and stars orbited a stationary Earth • Called Geocentric model or “Earth centered” • Occasionally a planet will move in the opposite direction in the sky called retrograde motion but the geocentric model cannot support this idea

5. Early Ideas cont… • In 1543, Copernicus suggested that the sun was the center of the solar system • Heliocentric model • This model supports the retrograde motion because the inner planets (closer to sun) move faster around the sun than outer planets • As faster planets pass slower ones, it appears the slower planets are moving backwards

6. Kepler’s First Law • Most scientists did not believe Copernicus but within a century, they were finding evidence to support his idea • Tycho Brahe made observations of the planets’ positions • Johannes Kepler used Brahe’s positions to demonstrate planets orbit the sun in an elliptic shape, rather than a circle • This is Kepler’s First Law

7. A ellipse is an oval shape that is centered on two points instead of a single point • The two points are the foci (singular: focus) • The major axis is the line that runs through both foci and is the maximum diameter of the ellipse • Each planet has a different elliptical shape and size but the sun is always at one focus

8. Eccentricity • A planet in an elliptical orbit is not at a constant distance from the sun • When a planet is closest to the sun, it is at perihelion, when it is farthest to the sun, it is at aphelion • The shape of a planet’s elliptical orbit is defined by eccentricity, which is the ratio of the distance between the foci and the length of the major axis

9. Eccentricity cont… • Eccentricity values range from 0 to 1 • A value of 0 is a perfect circle, and 1 is a very elongated oval • Most planets are not very eccentric, so their orbits are close to a circle • The length of time it takes for a planet to orbit around the sun is the orbital period

10. Kepler’s second law • Kepler also discovered that the imaginary line between the sun and planet sweeps out equal amounts of area in equal amounts of time The areas of all triangles are the same size.--Known as Kepler’s law of Equal Areas--

11. Kepler’s third law • Kepler developed a mathematical relationship between the size of a planet’s ellipse and its orbital period

12. Gravity and orbits • Isaac Newton developed an understanding of gravity by observing the Moon’s motion, the planets’ orbits, and the acceleration of falling objects on Earth • Newton realized that two bodies attract each other with a force that depends on their masses and the distance between two bodies

13. Law of universal gravitation • Every pair of bodies in the universe attracts each other with a force that is proportional to the product of their masses and inversely proportional to the square of the distance between them • Mass of Moon is 2x greater, and mass of Earth is 3x greater, the force of gravity would be 2x3= 6

14. Section 29.2 The terrestrial planets

15. Planet overview • Our planets can be grouped into two categories: • The first 4 planets are known as the terrestrial planets or the inner planets • Mercury, Venus, Earth, Mars • The last 4 planets are known as the gas giants or outer planets • Jupiter, Saturn, Uranus, Neptune

16. Planet terms • Rotational Period= length of one day • Orbital Period= length of one year • Albedo= amount of sunlight reflected from the surface

17. Mercury • Closest planet to the sun 35,980,000 miles away • No moons or rings • 1/3 the size of Earth • Orbital Period: 88 days • Rotational Period: 1407.6 hours • Mercury rotates so slowly that in two years, only 3 days have passed!

18. Mercury cont… • Essentially no atmosphere • Daytime Temperature: 700K (427 C) • Nighttime Temperature: 100K (-127 C) • Gravity: 38% of Earth ◦ ◦

19. Mercury cont… • Most knowledge of Mercury’s surface comes from Mariner 10 probe mission from 1974-75 • Heavily cratered and smooth plains from lava • Planetwide system of cliffs called scarps

20. Mercury cont… • High density of planet suggests Nickel-Iron core • Molten zone in interior • Believed Mercury was once larger

21. Venus • No moons • Brightest planet in Earth’s night sky because it is close and its albedo is .75 • Thick clouds surround the planet • Rotational Period: 243 days • Orbital Period: 225 days • Clockwise spin (opposite of most planets)

22. Venus cont… • 67,240,000 miles from sun • Venus has similar diameter, mass and density to earth • Day Temp: 737K (464C) • Hot enough to melt Lead! • Atmospheric pressure is 92 atmospheres vs. Earth’s 1!

23. Venus Cont… • Atmosphere: Carbon Dioxide, Nitrogen • Venus has clouds of sulfuric acid • Greenhouse effect causes gases to get trapped on Venus and make temperatures higher

24. venusCont… • Venus’ surface is smoothed by volcanic flows but has mountains, canyons and valleys • Large volcano Maat Mons • Current tectonic activity on Venus • Liquid metal core that extends halfway to surface • No measurable magnetic field

25. Earth • Distance from sun and nearly-circular orbit allow water in all 3 states • 78% Nitrogen, 21% oxygen atmosphere • Earth’s axis is tilted and wobbles while it spins • The wobble is called precession

26. Mars • Fourth Planet from sun • Called Red Planet for high Iron content in soil • Smaller and less dense than earth • Two irregular shaped moons • Captured asteroids

27. Mars cont… • Mars has been explored by telescopes and probes that have orbited, landed or flown by • Atmosphere: Carbon Dioxide and Nitrogen • Density and pressure are lower than Venus’ • Constant wind on Mars

28. Mars cont… • Southern hemisphere is a heavily cratered highland region • Northern hemisphere are sparsely cratered plains • Four gigantic shield volcanoes • Largest volcano is Olympus Mons • Base as large as Colorado • Largest mountain in solar system • 3x higher than Mt. Everest

29. Mars cont… • An enormous canyon, VallesMarineris lies on the equator • More than 4000 km • Dried river and lake beds, runoff channels • Suggest liquid water once flowed

30. Mars cont… • Small amount of ice at polar caps • CO2 ice (dry ice) and H2O ice under • Shrink and grow with Martian seasons • Seasons are from tilted axis and highly elongated orbit

31. Mars cont… • Core is Iron, Nickel and a little sulfur • Mars has no magnetic field so scientists hypothesize the core is solid • No tectonic plates or activity

32. Mars cont… • 141, 600,000 miles from sun • Orbital period: 687 days • Rotational period: 24 hours 40 minutes • Temperature range: 68 F to -220 F

33. Section 29.3 The gas Giants

34. Jupiter • Largest planet • 483,800,000 miles from sun • Mass is 11x larger than Earth and 10x smaller than the Sun • 70% of planetary matter • Its Bright! Albedo of .343 (34%) • Banded appearance from flow of atmosphere • Thin ring 6400 km wide

35. Jupiter cont… • Explored by several probes in the ‘70s • Low density for large size • Atmosphere is composed of Hydrogen and Helium • Elements remain in gas or liquid form • Liquid metallic hydrogen make up magnetic field

36. Jupiter cont… • Rotational Period: 9.8 hrs • Shortest day • Orbital Period: 11.86 years • Rapid rotation distorts planet size • Larger at equator • Clouds flow rapidly in alternating types • Belts are low, warm dark colored clouds • Zones are high, cool, light colored clouds

37. Jupiter cont… • Has an atmospheric storm raging for 400 years • Great Red Spot • Moons: 63 Known moons • Io, Europa, Ganymede and Callisto are largest • Larger than Earth’s moon and Pluto • Moons are made of ice and rock mixtures

38. Saturn • Second largest planet • Probes visited Saturn • Cassini mission launched in 1997 and arrived in 2004 • Planet density is lower than water • Rotates rapidly and has flowing belts and zones (clouds) • Atmosphere is hydrogen and Helium with ammonia ice near cloud tops

39. Saturn Cont… • Internally, fluid throughout with small solid core • Magnetic field is 1000x stronger than Earth’s • Magnetic field is aligned with its axis (unusual for planets)

40. Saturn cont… • Believe rings formed from particles of a destroyed moon • Saturn’s rings are brighter and broader than all planets’ rings • Composed of rock and ice pieces of varying sizes • 7 major rings made of smaller rings (ringlets) and gaps • Rings are thin and particles orbit at equatorial plane

41. Saturn cont… • 890,700,000 miles from sun • Rotational Period: 10.7 hours • Orbital Period: 29.5 years • 62 moons, 53 officially named • Titan, Saturn’s largest, is larger than our moon and has an atmosphere of methane and nitrogen

42. Uranus • Discovered accidentally in 1781 • 1,787,000,000 miles from sun • Rotational Period: 17 hours • Orbital Period: 84 years • The atmosphere keeps Uranus a chilly -353°F

43. Uranus cont… • Uranus has a blue velvety appearance • Atmosphere is made of Hydrogen, Helium, and Methane (CH4) • Methane reflects blue light into space • Few clouds present, no distinct belts or zones • Internal structure is liquid except for tiny frozen core

44. Uranus cont… • Strong magnetic field • Rotational axis is tipped so far its north pole is almost in orbital plane • Each pole spends 42 years in darkness and 42 years in sunlight due to the tilt • Think a giant collision knocked it sideways in its early years

45. Uranus cont… • Rings and moons orbit in the equatorial plane • 9 faint rings • Rings are “wobbly” • Uranus’ rings are dark, almost black making their discovery accidental • 15 moons

46. Uranus cont… • The Hubble telescope discovered a dark storm cloud • The storm was 2/3 the size of the US • Wind speeds on Uranus range from 90 to 360 mph

47. Neptune • Neptune was predicted before it was known to exist • Discovered in 1846 • 2,798,000,000 miles from sun • Rotational Period: 17.2 hours • Orbital Period: 165 years • Temp range: -240 to -370°F

48. Neptune cont… • Smaller and denser than Uranus, 4x larger than Earth • Strong magnetic field • Atmosphere of Hydrogen, Helium and Methane • Liquid interior with small frozen solid core

49. Neptune cont… • 13 Moons • Triton, Neptune’s largest Moon, is the only moon with a retrograde orbit (opposite direction) • Has active nitrogen geysers • 6 faint rings • Rings are uneven, thin and dark • Moons gravitational pull affects the rings

50. Neptune cont… • The Great Dark Spot is an Earth-sized hurricane • Size, shape, and location of the spot vary disappearing and reappearing occasionally • Spins counterclockwise • Horrendous winds near the spot were measured to be about 1,500 mph • Strongest winds in our solar system