19 Sept 2013 (Thursday), Week 5

Transcription

1 19 Sept 2013 (Thursday), Week 5 Astronomy Gordon Zwartz Chapter 4/5: Solar System and Earth and Moon Homework Assignment #5 Assigned : 19 Sept 13 (Thurs) Due: 26 Sept 13 (Thurs) (On-line: Mastering Astronomy) Reading Assignment (Assigned: 19 Sept 13): (Due: 24 Sept 13): Chapter 5: Earth and Moon Mastering Astronomy: (Course ID: MAZWARTZ13195 )

2 Homework Solutions will be posted on Physics Homepage.

3 Reading Assignment#5 Due Tuesday: 24 Sept 13 Read Chapter 5 (Earth and Moon). Write a summary of the main ideas (no more than ½ a page) and their meaning.

4 Homework#5 Due Thursday: 26 Sept 13 Chapter 4: Solar System Review and Discussion (RD): RD.1, RD.2, RD.6, RD.11, RD.15 Conceptual Self-Test (CST): CST.1, CST.3, CST.9, CST.11,CST.15 Activity: Does it matter that Pluto is designated a Dwarf Planet? Why or why not? Please back up answer with astronomical observations mentioned in the text. Bonus: Problems (P): P.1, P.5, P.7,and P.10

5 This Week In the News NASA Probe Finds Han Solo On Surface Of Mercury (PHOTO) Posted: 09/18/2013 3:56 pm EDT Updated: 09/18/2013 3:57 pm EDT NASA's Messenger probe, dispatched to study Mercury in 2004, has stumbled across an intriguing image on the planet's surface: that of the fictional "Star Wars" character Han Solo, encased in carbonite.

6 This Week In the News

7 This Week In the News Asteroid 2013 RZ53 To Pass Between Earth & Moon This Week (VIDEO) Space.com By Megan Cannon Posted: 09/17/ :04 am EDT Researchers think that 2013 RZ53 is a member of the Apollo family of near-earth asteroids. The meteor that exploded over the Russian city of Chelyabinsk in February is suspected to be part of this group. The Russian meteor was much larger than 2013 RZ53, at an estimated 56 to 66 feet wide (17 to 20 m).

8 This Week In the News Researchers think that 2013 RZ53 is a member of the Apollo family of near-earth asteroids. The meteor that exploded over the Russian city of Chelyabinsk in February is suspected to be part of this group. The Russian meteor was much larger than 2013 RZ53, at an estimated 56 to 66 feet wide (17 to 20 m).

9 This Week In the News

10 Interplanetary Matter

11 Common Characteristics and Exceptions

12 Interplanetary Matter The inner solar system, showing the asteroid belt, Earth-crossing asteroids, and Trojan asteroids

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14 Kuiper Belt Objects These large, icy bodies have orbits similar to the smaller objects in the Kuiper Belt that become short-period comets. So are they very large comets or very small planets?

15 Asteroids

16 Asteroid Facts Asteroids are rocky leftovers of planet formation. Largest is Ceres, diameter ~1,000 km 150,000 in catalogs, and probably over a million with diameter >1 km. Small asteroids are more common than large asteroids. All the asteroids in the solar system wouldn t add up to even a small terrestrial planet.

17 Asteroids are cratered and not round

18 ASTEROID: Object of rock or metal, smaller than a planet, orbiting the Sun. METEOROID: Object of rock or metal, smaller than an asteroid, orbiting the Sun. (Objects less than a few hundred meters across qualify as meteoroids.)

19 Meteoroids occasionally collide with Earth. METEOR: Streak of light produced as a meteoroid enters the Earth s atmosphere. METEORITE: Remnant of a meteoroid that survives the passage through the Earth s atmosphere.

20 The Earth sweeps up 300 tons of meteoroids every day. Most meteoroids are vaporized by friction in the atmosphere. Only meteoroids over an inch across survive the plunge and become meteorites.

21 Meteorites are usually asteroid fragments that 95% of all meteorites are stony meteorites (with spectra similar to rocky asteroids). It is sometimes hard to tell stony meteorites from plain Earth rocks. New Concord, OH, ordinary chondrite. May 1, 1860 have struck the Earth.

22 4% of all meteorites are iron meteorites (with spectra similar to metal-rich asteroids). Iron meteorites can be found with a metal detector. The remaining 1% of meteorites are stony iron meteorites.

23 How are meteorites related to asteroids?

24 How are meteorites related to asteroids? Meteorites are pieces of asteroids - or sometimes planets or the Moon.

25 Pieces of Asteroids:Meteorite Types 1) Primitive: Unchanged in composition since they first formed 4.6 billion years ago. 2) Processed: Younger, have experienced processes like volcanism or differentiation.

26 Primitive Meteorites: simple, all ingredients mixed together

27 Processed Meteorites: shattered fragments of larger objects Iron from a core Volcanic rock from a crust or mantle

28 What do we learn from meteorites? primitive meteorites tell us when solar system formation began. Processed meteorites tell us what asteroids are like on the inside. Processed meteorites provide direct proof that differentiation and volcanism happened on asteroids.

29 Meteorites from Moon and Mars A few meteorites arrive from the Moon and Mars Composition differs from the asteroid fragments. A cheap (but slow) way to acquire moon rocks and Mars rocks. One Mars meteorite generated a stir when scientists claimed evidence for microscopic life in it.

30 Why is there an asteroid belt?

31 More than 150,000 asteroids at their predicted locations for Jan On this scale, asteroids are much smaller than the dots used to represent them

32 Asteroid Orbits Most asteroids orbit in a belt between Mars and Jupiter. Trojan asteroids follow Jupiter s orbit. Orbits of near- Earth asteroids cross Earth s orbit.

33 Rocky planetesimals survived in the asteroid belt between Mars and Jupiter because they did not accrete into a planet. Jupiter s gravity, stirs up the asteroid orbits and prevents their planet formation.

34 Asteroids are not uniformly distributed through the asteroid belt. For certain orbit size, there are very few asteroids. (These gaps in the distribution are called Kirkwood gaps.)

35 (2) Asteroids are strongly influenced by the gravity of Jupiter. Kirkwood gaps are caused by an orbital resonance with Jupiter. (Similar to the orbital resonance that creates gaps in Saturn s rings.)

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37 Two groups of asteroids precede and follow Jupiter on its orbit. They are called the Trojan asteroids (named after Homeric heroes).

38 Trojan asteroids are kept from straying by the combined gravity of Sun and Jupiter. Jupiter has some 1800 known Trojan asteroids (1100 Greeks and 700 Trojans).

39 Lagrange Points A contour plot of the effective potential due to gravity and the centrifugal force of a two-body system in a rotating frame of reference. The arrows indicate the gradients of the potential around the five Lagrange points downhill toward them (red) or away from them (blue). Counterintuitively, the L 4 and L 5 points are the high points of the potential. At the points themselves these forces are balanced.

40 Orbital Resonances Asteroids in orbital resonance with Jupiter experience periodic nudges. Eventually those nudges move asteroids out of resonant orbits, leaving gaps in the belt.

41 Why are there very few asteroids beyond Jupiter s orbit? A. There was no rocky material beyond Jupiter s orbit. B. The heaviest rocks sank towards the center of the solar system. C. Ice could form in the outer solar system. D. A passing star probably stripped away all of those asteroids, even if they were there at one time.

42 Why are there very few asteroids beyond Jupiter s orbit? A. There was no rocky material beyond Jupiter s orbit. B. The heaviest rocks sank towards the center of the solar system. C. Ice could form in the outer solar system. D. A passing star probably stripped away all of those asteroids, even if they were there at one time.

43 What have we learned? Why is there an asteroid belt? Orbital resonances with Jupiter disrupted the orbits of planetesimals, preventing them from accreting into a planet. Those that were not ejected from this region make up the asteroid belt today. Most asteroids in other regions of the inner solar system accreted into one of the planets. How are meteorites related to asteroids? Most meteorites are pieces of asteroids. Primitive meteorites are essentially unchanged since the birth of the solar system. Processed meteorites are fragments of larger asteroids that underwent differentiation.

44 Question 5 Most asteroids are found a) beyond the orbit of Neptune. b) between Earth and the Sun. c) between Mars and Jupiter. d) in the orbit of Jupiter, but 60 degrees ahead or behind it. e) orbiting the jovian planets in captured, retrograde orbits.

45 Question 5 Most asteroids are found a) beyond the orbit of Neptune. b) between Earth and the Sun. c) between Mars and Jupiter. d) in the orbit of Jupiter, but 60 degrees ahead or behind it. e) orbiting the jovian planets in captured, retrograde orbits. The Asteroid Belt is located between 2.1 and 3.3 A U from the Sun.

46 Question 6 The asteroid belt is evidence of a) a planet that once orbited the Sun but later was destroyed. b) ancient material from the formation of the solar system. c) a collision between Jupiter and one of its larger moons. d) comets that were trapped by Jupiter s gravitational field.

47 Question 6 The asteroid belt is evidence of a) a planet that once orbited the Sun but later was destroyed. b) ancient material from the formation of the solar system. c) a collision between Jupiter and one of its larger moons. d) comets that were trapped by Jupiter s gravitational field. Asteroids, meteoroids, and comets may have not changed at all since the solar system formed.

48 Interplanetary Matter Meteor showers are associated with comets they are the debris left over when a comet breaks up.

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50 Interplanetary Matter

51 Interplanetary Matter The impact of a large meteor can create a significant crater. The Barringer meteor crater in Arizona

52 Interplanetary Matter The Manicouagan reservoir in Quebec

53 What Killed the Dinosaurs? The dinosaurs may have been killed by the impact of a large meteor or small asteroid. The larger an impact is, the less often we expect it to occur.

54 Impacts will certainly occur in the future, and while the chance of a major impact in our lifetimes is small, the effects could be devastating.

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56 Have we ever witnessed a major impact?

57 Comet SL9 caused a string of violent impacts on Jupiter in 1994, reminding us that catastrophic collisions still happen. Tidal forces tore it apart during previous encounter with Jupiter

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60 Impact plume rises high above Jupiter s surface

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64 Did an impact kill the dinosaurs?

65 Mass Extinctions Large dips in total species diversity in the fossil record. The most recent was 65 million years ago, ending the reign of the dinosaurs. Was it caused by an impact? How would it have happened?

66 No dinosaur fossils in these rock layers Thin layer containing iridium from impactor Dinosaur fossils in lower rock layers

67 Iridium - evidence of an impact Iridium is very rare in Earth surface rocks but often found in meteorites. Luis and Walter Alvarez found a worldwide layer containing iridium, laid down 65 million years ago.

68 Comet or asteroid about 10km in diameter approaches Earth

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73 An iridium-rich sediment layer and an impact crater on the Mexican coast 65 million years ago. shows that a large impact occurred at the time the dinosaurs died out,

74 The Impact Threat: Real danger or media hype?

75 Facts Asteroids and comets have hit the Earth. A major impact is only a matter of time: not IF but WHEN. Major impact are very rare. Extinction level events ~ millions of years. Major damage ~ tens-hundreds of years.

76 Tunguska, Siberia: June 30, 1908 The ~40 meter object disintegrated and exploded in the atmosphere

77 Meteor Crater, Arizona: 50,000 years ago (50 meter object)

78 The asteroid with our name on it We haven t seen it yet. Deflection is more probable with years of advance warning. Control is critical: breaking a big asteroid into a bunch of little asteroids is unlikely to help. We get less advance warning of a killer comet

79 How do other planets affect impact rates and life on Earth?

80 Gravity from Jovial planets can influence the path of comets and Asteroids. They could protect us or steer one in our direction

81 What have we learned? How do other planets affect impact rates and life on Earth? Impacts of asteroids and comets are always linked in at least some way to the gravitational influences of Jupiter and the other Jovian planets. These gravitational influences have shaped the asteroid belt, the Kuiper belt, and the Oort cloud, and sometimes still help determine when an object is flung our way.

82 Comets

83 Comet Facts Formed beyond the frostline, comets are icy counterparts to asteroids. Dirty snowballs = the nucleus Most comets do not have tails. Most comets remain perpetually frozen in the outer solar system. Only a few enter the inner solar system, where they can grow tails.

84 Interplanetary Matter Comets are icy, with some rocky parts. The basic components of a comet

85 Interplanetary Matter The solar wind means the ion tail always points away from the Sun. The dust tail also tends to point away from the Sun, but the dust particles are more massive and lag somewhat, forming a curved tail.

86 Interplanetary Matter The internal structure of the cometary nucleus

87 Interplanetary Matter The size, shape, and orientation of cometary orbits depend on their location. Oort cloud comets rarely enter the inner solar system.

88 When a comet nears the Sun, its ices can sublimate into gas and carry off dust, creating a coma and long tails.

89 Draw This Picture

90 Comets eject small particles that follow the comet around in its orbit This can cause meteor showers when Earth crosses the comet s orbit.

91 Meteors in a shower appear to emanate from the same area of sky because of Earth s motion through space

92 Question 8 What causes a meteor shower? a) A comet and an asteroid collide. b) Earth runs into a stray swarm of asteroids. c) Earth runs into the debris of an old comet littering its orbit. d) Meteorites are ejected from the Moon. e) Debris from a supernova enters Earth s atmosphere

93 Question 8 What causes a meteor shower? a) A comet and an asteroid collide. b) Earth runs into a stray swarm of asteroids. c) Earth runs into the debris of an old comet littering its orbit. d) Meteorites are ejected from the Moon. e) Debris from a supernova enters Earth s atmosphere Meteor showers can generate a few shooting stars, to hundreds of thousands, seen in an hour.

94 Question 7 Compared to asteroids, comets show all of these properties EXCEPT a) their densities are higher. b) their orbits tend to be more elliptical. c) they tend to be made of ice. d) they can look fuzzy, whereas asteroids appear as moving points of light. e) their average distances from the Sun are far greater.

95 Question 7 Compared to asteroids, comets show all of these properties EXCEPT a) their densities are higher. b) their orbits tend to be more elliptical. c) they tend to be made of ice. d) they can look fuzzy, whereas asteroids appear as moving points of light. e) their average distances from the Sun are far greater. Comets have densities much lower than asteroids or planets.

96 Where do comets come from?

97 Only a tiny number of comets enter the inner solar system - most stay far from the Sun Oort cloud: On random orbits extending to about 50,000 AU Kuiper belt: On orderly orbits from AU in disk of solar system

98 How did they get there? Kuiper belt comets align with the plane of planet orbits Oort Cloud Comets were kicked out of the solar system by the gravity from Jovian planets: random orbits

99 What have we learned? Vast majority of comets do not have tails. Only those few comets that enter the solar system grow tails. As the comet approaches the Sun its nucleus heats up. Some of the comet s ice sublimates into gas, and the escaping gases carry along some dust. The gas and dust form a coma and two tails: a plasma tail of ionized gas and a dust tail. Larger particles can also escape, becoming the particles that cause meteors and meteor showers on Earth.

100 Question 9 Any theory of the origin of the solar system must explain all of these EXCEPT a) the orbits of the planets are nearly circular, and in the same plane. b) the direction that planets orbit the Sun is opposite to the Sun s spin. c) the terrestrial planets have higher density and lower mass. d) comets do not necessarily orbit in the plane of the solar system.

101 Question 9 Any theory of the origin of the solar system must explain all of these EXCEPT a) the orbits of the planets are nearly circular, and in the same plane. b) the direction that planets orbit the Sun is opposite to the Sun s spin. c) the terrestrial planets have higher density and lower mass. d) comets do not necessarily orbit in the plane of the solar system. The planets do orbit in the same direction that the Sun spins. Most also spin in that direction, and most also have large moons that orbit in that direction.

102 Formation of Solar System

103 Angular Momentum Conservation of angular momentum says that product of radius and rotation rate must be constant

104 The Concept of Angular Momentum As a dust cloud collapses, its rate of rotation will increase.

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107 Data that Needs to be explained:

108 Data that Needs to be explained: 1. Planets isolated 2. Orbits ~circular / in ~same plane 3. Planets (and moons) travel along orbits in same direction. same direction as Sun rotates (counterclockwise viewed from above) Lunar and Planetary Institute image at

109 More data to be explained: 4. Most planets rotate in this same direction Mercury 0 Venus 177 Earth 23 Mars 25 Jupiter 3 Saturn 27 Uranus 98 Neptune 30 NASA images edited by LPI

110 Still more data to be explained: 5. Solar System highly differentiated: Terrestrial Planets (rocky, dense with density ~4-5 g/cm3) Jovian Planets (light, gassy, H, He, density 0.7-2) Images: Lunar and Planetary Laboratory:

111 Origin of the Solar System

112 Origin of the Solar System

113 Stars spew out 1/2 their mass as gas & dust as they die

114 In the interstellar medium, dust and gas coalesces into clouds

115 New generations of stars (and their planets, if any) form in these clouds

116 The Formation of the Solar System Temperature in cloud determines where various materials condense out; this determines where rocky planets and gas giants form.

117 What Caused the Intra-Stellar Gas to Collapse into our Solar System?

118 #1 Nebular theory: Interstellar cloud of gas & dust collapsed under its own gravity Prediction: protoplanetary nebulae should be observed Explains all of the major features of solar system, and also the exceptions Observations continue to support this theory

119 How Did the Solar System Form? Nebular contraction: Cloud of gas and dust contracts due to gravity; conservation of angular momentum means it spins faster and faster as it contracts

120 How Did the Solar System Form? 1. Nebular contraction is followed by condensation around dust grains, known to exist in interstellar clouds such as the one shown here. 2. Accretion then leads to larger and larger clumps; finally gravitational attraction takes over and planets form.

121 The next billion years: Debris disks Gas and fine dust blows away after ~ 10 million years Jupiter must have formed by then Older stars have debris disks around them Need a supply of larger objects to regenerate the dust that gets blown away evidence of planets forming around other stars Debris disks are analogous to the Oort cloud and Kuiper belt of comets, and the asteroid belt

122 Debris disks around stars > 100 million years old are very common!

123 #2 Condensation theory: Interstellar dust grains help cool cloud, and act as condensation nuclei.

124 But How?

125 Planetary Nebula or Close Encounter? Historically, two hypothesis were put forward to explain the formation of the solar system. Gravitational Collapse of Planetary Nebula (Latin for cloud ) Solar system formed form gravitational collapse of an interstellar cloud or gas Close Encounter (of the Sun with another star) Planets are formed from debris pulled out of the Sun during a close encounter with another star. But, it cannot account for The angular momentum distribution in the solar system, Probability for such encounter is small in our neighborhood

126 The Interstellar Clouds The primordial gas after the Big Bang has very low heavy metal content The interstellar clouds that the solar system was built from gas that has gone through several star-gas-star cycles.

127 Collapse of the Solar Nebula Gravitational Collapse Denser region in a interstellar cloud, maybe compressed by shock waves from an exploding supernova, triggers the gravitational collapse. 1. Heating Prototsun Sun In-falling materials loses gravitational potential energy, which were converted into kinetic energy. The dense materials collides with each other, causing the gas to heat up. Once the temperature and density gets high enough for nuclear fusion to start, a star is born. 2. Spinning Smoothing of the random motions Conservation of angular momentum causes the in-falling material to spin faster and faster as they get closer to the center of the collapsing cloud. 3. Flattening Protoplanetary disk. The solar nebular flattened into a flat disk. Collision between clumps of material turns the random, chaotic motion into a orderly rotating disk. This process explains the orderly motion of most of the solar system objects!

128 Question 10 The condensation sequence theory explains why a) our planet Earth has water and rain. b) stars are more likely to form large planets orbiting very near. c) terrestrial planets are different from jovian planets. d) the Moon formed near the Earth. e) Pluto has such a circular orbit.

129 Question 10 The condensation sequence theory explains why a) our planet Earth has water and rain. b) stars are more likely to form large planets orbiting very near. c) terrestrial planets are different from jovian planets. d) the Moon formed near to Earth. e) Pluto has such a circular orbit. The condensation sequence theory explains how the temperature of the early solar nebula controls which materials are solid, and which are gaseous.

130 The Formation of the Solar System The star Beta Pictoris is surrounded by a disk of warm matter, which may indicate planetary formation.

131 The Formation of the Solar System These images show possible planetary systems in the process of formation.

132 How Did We Get a Solar System? Image: LPI Concentrations of dust and gas in the cloud; material starts to collect (gravity > magnetic forces) Hubble image at

133 How Did We Get a Solar System? Gravity concentrates most stuff near center Heat and pressure increase Collapses central proto-sun rotates faster (probably got initial rotation from the cloud) Image: LPI

134 How Did We Get a Solar System? Rotating, flattening, contracting disk - solar nebula! Equatorial Plane Orbit Direction NASA artwork at

135 After ~10 million years, material in center of nebula hot enough to fuse H...here comes the sun NASA/JPL-Caltech Image at

136 Condensation Theory: Terrestrial / Jovian Metallic elements (Mg, Si, Fe) condense into solids at high temps. Combined with O to make tiny grains Lower temp (H, He, CH4, H2O, N2, ice) - outer edges Planetary Compositions Hubble photo at

137 How Did We Get a Solar System? Inner Planets: Hot Silicate minerals, metals, no light elements, ice Begin to stick together with dust clumps Image: LPI

138 How Did We Get a Solar System? Accretion - particles collide and stick together or break apart gravity not involved if small pieces Form planetesimals, up to a few km across Image: LPI

139 How Did We Get a Solar System? Gravitational accretion: planetesimals attract stuff Large protoplanets dominate, grow rapidly, clean up area ( takes ~10 to 25 My) Image: LPI

140 How Did We Get a Solar System? Outer Solar System Cold ices, gases 10x more particles than inner May have formed icy center, then captured lighter gases (Jupiter and Saturn first? Took H and He?) Image: LPI

141 Gravitational accretion of gas for protoplanets in the coolest nebular parts Image: LPI How Did We Get a Solar System? Early burst of solar wind - sweeps debris out of system

142 Early in the Life of Planets Planetesimals swept up debris Accretion + Impacts = HEAT Eventually begin to melt materials Iron, silica melt at different temperatures Iron sank density layering Image from LPI:

143 Planetary Interiors Image from LPI: Differentiation Separation of homogenous interior into layers of different compositions Early hottest time dense iron-rich material core Releases additional heat Leaves mantle with molten ocean enriched in silica Crust eventually forms from lightest material

144 How Old is the Solar System?

145 4.56 billion years ago How do we know? (evidence for formation) Lunar samples to 4.6 Ga Meteorites Ga Earth 3.9 (or 4.4 Ga) Lunar meteorite at Meteorite photo by Carl Allen at

146 Earliest history of Solar System - chemical and physical info about formation and building blocks of planets (rest of stuff was pulled into the Sun or other planets.) Sample Return 1/15/2006 Stardust Passed through Comet Wild 2 Coma 1/2004 Stardust image at Info and images at