Announcement Test 2 is coming up on Mar 19. Start preparing! This test will cover the classes from Feb 27 - Mar 14. 50 points, scantron, 1 hr. 1
AST103 Ch. 7 Our Planetary System Earth, as viewed by the Voyager spacecraft 2
7.1 Studying the Solar System Our goals for learning: What does the solar system look like? What can we learn by comparing the planets to one another? What are the major features of the Sun and planets? 3
Comparative Planetology We can learn more about a world like our Earth by studying it in context with other worlds in the solar system. Stay focused on processes common to multiple worlds instead of individual facts specific to a particular world. Comparing the planets reveals patterns among them. Those patterns provide insights that help us understand our own planet. 4
Terrestrial planets Jovian planets Eight major planets with nearly circular orbits. Pluto is smaller than the major planets and has a more elliptical orbit. 5
Two Main Planet Types Terrestrial planets are rocky, relatively small, and close to the Sun Jovian planets are gaseous, larger, and farther from Sun 6
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textbook p.213 8
p.9 Figure 1.6 Washington D.C. Planets are very tiny compared to distances between them. 9
Sun Over 99.9% of solar system s mass Made mostly of H/He gas (plasma) Converts 4 million tons of mass into energy each second 10
Mercury 0.39 AU from Sun size: 0.38 REarth mass: 0.055 MEarth density: 5.43 g/cm 3 closest to the Sun smallest among 8 planets Made of metal and rock; large iron core Desolate, cratered; long, tall, steep cliffs Very hot and very cold: 425 C (day), 170 C (night) 11
Venus 0.72 AU from Sun size: 0.95 REarth mass: 0.82 MEarth density: 5.24 g/cm 3 Nearly identical in size to Earth; surface hidden by clouds Hellish conditions due to an extreme greenhouse effect Even hotter than Mercury: 470 C, day and night 12
Earth 1 AU from Sun density: 5.52 g/cm 3 Earth and Moon to scale Size: Rmoon ~ REarth / 4 Mass: Mmoon ~ MEarth / 80 An oasis of life The only surface liquid water in the solar system Largest of the terrestrial planets 13
Mars 1.52 AU from Sun size: 0.53 REarth mass: 0.11 MEarth density: 3.93 g/cm 3 Looks almost Earth-like, but don t go without a spacesuit! Giant volcanoes, a huge canyon, polar caps, more Water flowed in distant past; could there have been life? 14
http://marsrovers.jpl.nasa.gov/home/index.html 15
March 7, 2012 Press release: Dust devil on Mars 16
http://www.google.com/mars/ 17
Jupiter 5.20 AU from Sun size: 11.2 REarth mass: 318 MEarth density: 1.33 g/cm 3 largest and heaviest Much farther from Sun than inner planets Mostly H/He; no solid surface 300 times more massive than Earth Many moons 18
Jupiter s moons can be as interesting as planets themselves, especially Jupiter s four Galilean moons Io (shown here): Active volcanoes all over. Europa: Possible subsurface ocean Ganymede: Largest moon in solar system Callisto: A large, cratered ice ball 19
Saturn 2nd largest 9.54 AU from Sun size: 9.4 REarth mass: 95.2 MEarth density: 0.70 g/cm 3 Giant and gaseous like Jupiter Spectacular rings Many moons, including cloudy Titan (larger than Mercury) 20
Saturn Rings Artist s conception Rings are NOT solid; they are made of countless small chunks of ice and rock, each orbiting like a tiny moon. 21
Uranus 19.2 AU from Sun size: 4.0 REarth mass: 14.5 MEarth density: 1.32 g/cm 3 Smaller than Jupiter/Saturn; much larger than Earth Made of H/He gas & hydrogen compounds (H 2 O, ammonia, methane) Extreme axis tilt Moons & rings 22
Neptune 30.1 AU from Sun size: 3.9 REarth mass: 17.1 MEarth density: 1.64 g/cm 3 Similar to Uranus (except for axis tilt) Many moons (including Triton [larger than Pluto]) Only Voyager2 visited Uranus and Neptune 23
Pluto (and other Dwarf Planets) Pluto 39.5 AU from Sun size: 0.18 REarth mass: 0.0022 MEarth density: 2.0 g/cm 3 Pluto and its moons, as photographed by the HST Much smaller than major planets Icy, comet-like composition Pluto s main moon (Charon) is of similar size 24
NEW HORIZONS mission to Pluto 25
Patterns of Motion All planetary orbits are nearly circular and lie nearly in the same plane. All planets orbit the Sun in the same direction: counterclockwise as viewed from high above the Earth s North Pole. Most planets rotate in the same direction in which they orbit with fairly small axis tilts. The Sun also rotates in the same direction. Most of the solar system s large moons exhibit similar properties in their orbits around their planets -- orbiting in their planet s equatorial plane in the same direction that the planet rotates. 26
What have we learned? What does the solar system look like? Planets orbit Sun in the same direction and in nearly the same plane. What can we learn by comparing the planets to one another? Comparative planetology looks for patterns among the planets. Those patterns give us insight into the general processes that govern planets Studying other worlds in this way tells us about our own Earth 27
What have we learned? What are the major features of the Sun and planets? Sun: Over 99.9% of the mass Mercury: A hot rock Venus: Same size as Earth but much hotter Earth: Only planet with liquid water on surface Mars: Could have had liquid water in past Jupiter: A gaseous giant Saturn: Gaseous with spectacular rings Uranus: A gas giant with a highly tilted axis Neptune: Similar to Uranus but with normal axis Dwarf Planets: Most (like Pluto) are icy like comets 28
Quiz The largest (in size) terrestrial planet and jovian planet are, respectively, A) Venus and Jupiter B) Earth and Jupiter C) Earth and Puto 29
The Sun 30
http://sohowww.nascom.nasa.gov/ 31
Properties of the Sun Radius Mass Luminosity ~7x10 5 km (~110 REarth) 2x10 30 kg (~3x10 5 MEarth) 3.8x10 26 W Composition Temperature Rotation Rate Age 70% hydrogen 28% helium, 2% heavier elements ~6000 K (average surface) 4,500 K (sunspots), 1.5x10 7 K (core) 25 days (equator) 30 days (pole) ~4.6 billion yrs A ball of plasma! 32
The Sun is the Largest Object in the Solar System The Sun contains more than 99.9% of the total mass of the solar system If you put all the planets into the Sun, they would not fill up its volume ~110 Earths or 10 Jupiters fit across the diameter of the Sun 33
Structure of the Sun From outside to inside: - solar wind - corona - chromosphere - photosphere ~10 6 K - convection zone - radiation zone - core ~10 4 K ~6000 K ~10 7 K ~1.5x10 7 K density 100 g/cm 3 34
How does Sun shine? Nuclear Fusion + + + + + + mass of 4 protons: 6.6943 x 10-27 kg mass of helium nucleus: 6.6466 x 10-27 kg difference in mass: 0.0477 x 10-27 kg ( 1 H= one proton, 4 He=2 protons + 2 neutrons) 35
This mass difference is the energy source of the Sun! E=mc 2 (Einstein 1905) Special Theory of Relativity energy = mass x (speed of light) 2 E = 0.0477 x 10-27 kg x (3x10 8 m/s) 2 = 4.3 x 10-12 Joules Tiny amount of energy, but MANY of these reactions take place in the core of the Sun! 36
Quiz How was the chemical composition of the Sun 3 billion years ago different than what it is today? A. It had more hydrogen then. B. It had more helium then. C. It had more nitrogen then. D. It had more oxygen then. 37
Lecture-Tutorial (LT): Sun Size (pp. 105-107) Work with a partner! Read the instructions and questions carefully. Discuss the concepts and your answers with one another. Come to a consensus answer you both agree on. If you get stuck or are not sure of your answer, ask another group. If you get really stuck or don t understand what the LT is asking, ask one of us for help. 38
Sunspots They come in pairs. They move with the rotation of the Sun 39
Sunspots 40
Convective Zone 41
Granules in the Photosphere Caused by rising & sinking in the convective zone hot --> rise --> light cold --> sink --> dark Movie: http://science.nasa.gov/ssl/pad/solar/images/svst_granulation.mpg 42
Sunspots are caused by bundled magnetic fields Sunspots are cooler (4500 K) that s why they look black (just a contrast) magnetic fields constrain the flow of gas 43
See this and other SOHO movies at http://sohowww.nascom.nasa.gov/ 44
Solar cycles 7-15 yr cycle; average 11 year cycle # of sunspots correlate with solar cycle 45