Formation of the Solar System and Other Planetary Systems

1 Questions to Ponder

1. Are all the other planets similar to , or are they very different? 2. Do other planets have moons like Earth’s Moon? 3. How do astronomers know what the other planets are made of? 4. Are all the planets made of basically the same material? 5. What is the difference between an and a ? 6. Why are craters common on the Moon but rare on the Earth? 7. Why do interplanetary spacecraft carry devices for measuring magnetic fields? 8. Do all the planets have a common origin?

2 Questions to Ponder about Origins

1. What must be included in a viable theory of the origin of the solar system? 2. Why are some elements (like gold) quite rare, while others (like carbon) are more common? 3. How do we know the age of the solar system? 4. How do astronomers think the solar system formed? 5. Did all of the planets form in the same way? 6. Are there planets orbiting other stars? How do astronomers search for other planets?

3 There are two broad categories of planets: Earthlike (terrestrial) and Jupiterlike (jovian)

• All of the planets orbit the Sun in the same direction and in almost the same plane • Most of the planets have nearly circular orbits

4 Density • The average density of any substance depends in part on its composition • An object sinks in a fluid if its average density is greater than that of the fluid, but rises if its m average density is less than that of the fluid • The terrestrial (Earth-like) planets are made of D  rocky materials and have dense iron cores, which gives these planets high average densities V • The Jovian (Jupiter-like) planets are composed primarily of light elements such as hydrogen and helium, which gives these planets low average densities

5 The Terrestrial Planets

• The four innermost planets are called terrestrial planets – Relatively small (with diameters of 5000 to 13,000 km) – High average densities (4000 to 5500 kg/m3) – Composed primarily of rocky materials 6 Jovian Planets are the outer planets EXCEPT for Pluto

• Jupiter, Saturn, Uranus and Neptune are Jovian planets – Large diameters (50,000 to 143,000 km) – Low average densities (700 to 1700 kg/m3) 7 – Composed primarily of hydrogen and helium. iClicker Question

How can one calculate the density of a planet? A Use Kepler's Law to obtain the weight of the planet. B Divide the total mass of the planet by the volume of the planet. C Divide the total volume of the planet by the mass of the planet. D Multiply the planet's mass by its weight. E Multiply the total volume by the mass of the planet.

8 Pluto (dwarf planet) - Not terrestrial nor Jovian •Pluto is a special case –Smaller than any of the terrestrial planets –Intermediate average density of about 1900 kg/m3 –Density suggests it is composed of a mixture of ice and rock

9 iClicker Question

The terrestrial planets include the following: A Mercury, , Earth, and Pluto B Jupiter, Saturn, Uranus, Neptune and Pluto C Jupiter, Saturn, Uranus and Neptune D Earth only E Mercury, Venus, Earth and Mars

10 iClicker Question

The jovian planets include the following: A Mercury, Venus, Earth, Mars and Pluto B Jupiter, Saturn, Uranus, Neptune and Pluto C Jupiter, Saturn, Uranus and Neptune D Earth only E Mercury, Venus, Earth and Mars

11 iClicker Question

Which of these planets is least dense? A Jupiter B Neptune C Pluto D Uranus E Saturn

12 Seven largest satellites are almost as big as the terrestrial planets

• Some (3) comparable in size to the planet Mercury (2 are larger) 13 • The remaining moons of the solar system are much smaller than these Spectroscopy reveals the chemical composition of the planets

• The spectrum of a planet or satellite with an atmosphere reveals the atmosphere’s composition • If there is no atmosphere, the spectrum indicates the composition of the surface. • The substances that make up the planets can be classified as gases, ices, or rock, depending on the temperatures and pressures at which they solidify • The terrestrial planets are composed primarily of rocky materials, whereas the Jovian planets are composed largely of gas

14 Phases and Phase Diagram (Not in text but important)

15 Spectroscopy of Titan (moon of Saturn)

16 Spectroscopy of Titan (moon of Saturn)

17 Spectroscopy of (moon of Jupiter)

18 Hydrogen and helium are abundant on the Jovian planets, whereas the terrestrial planets are composed mostly of heavier elements

Jupiter Mars

19 (rocky) and (icy) also orbit the Sun

• Asteroids are small, rocky objects • Comets and Objects are made of “dirty ice” • All are remnants left over from the formation of the planets • The Kuiper belt extends far beyond the orbit of Pluto • Pluto (aka dwarf planet) can be thought of as a large member of the Kuiper Belt 20 Cratering on Planets and Satellites • Result of impacts from interplanetary debris – when an asteroid, comet, or collides with the surface of a terrestrial planet or satellite, the result is an impact crater • Geologic activity renews the surface and erases craters – extensive cratering means an old surface and little or no geologic activity – geologic activity is powered by internal heat, and smaller worlds lose heat more rapidly, thus, as a general rule, smaller terrestrial worlds are more extensively cratered

21 Craters on the Moon

22 A planet with a magnetic field indicates an interior in motion

• Planetary magnetic fields are produced by the motion of electrically conducting substances inside the planet • This mechanism is called a dynamo • If a planet has no magnetic field this would be evidence that there is little such material in the planet’s interior or that the substance is not in a state of motion

23 • The magnetic fields of terrestrial planets are produced by metals such as iron in the liquid state

• The magnetic fields of the Jovian planets are generated by metallic hydrogen

24 iClicker Question

The presence of Earth’s magnetic field is a good indication that A there is a large amount of magnetic material buried near the North Pole. B there is a quantity of liquid metal swirling around in the Earth's core. C the Earth is composed largely of iron. D the Earth is completely solid. E there are condensed gasses in the core of the Earth.

25 The diversity of the solar system is a result of its origin and evolution

• The planets, satellites, comets, asteroids, and the Sun itself formed from the same cloud of interstellar gas and dust • The composition of this cloud was shaped by cosmic processes, including nuclear reactions that took place within stars that died long before our solar system was formed • Different planets formed in different environments depending on their distance from the Sun and these environmental variations gave rise to26 the planets and satellites of our present- solar system iClicker Question

Understanding the origin and evolution of the solar system is one of the primary goals of A relativity theory. B seismology. C comparative planetology. D mineralogy. E oceanography.

27 iClicker Question

In general, which statement best compares the densities of the terrestrial and jovian planets. A Both terrestrial and jovian planets have similar densities. B Comparison are useless because the jovian planets are so much larger than the terrestrials. C No general statement can be made about terrestrial and jovian planets. D The jovian planets have higher densities than the terrestrial planets. E The terrestrial planets have higher densities than the jovian planets. 28 Any model of solar system origins must explain the present-day Sun and planets

1. The terrestrial planets, which are composed primarily of rocky substances, are relatively small, while the Jovian planets, which are composed primarily of hydrogen and helium, are relatively large 2. All of the planets orbit the Sun in the same direction, and all of their orbits are in nearly the same plane 3. The terrestrial planets orbit close to the Sun, while the Jovian planets orbit far from the Sun

29 The abundances of the chemical elements are the result of cosmic processes

• The vast majority of the atoms in the universe are hydrogen and helium atoms produced in the Big Bang 30 All heavy elements (>Li) were manufactured by stars after the origin of the universe itself, either by fusion deep in stellar interiors or by stellar explosions.

31 • The interstellar medium is a tenuous collection of gas and dust that pervades the spaces between the stars • A nebula is any gas cloud in interstellar space 32 The abundances of radioactive elements reveal the solar system’s age

• Each type of radioactive nucleus decays at its own characteristic rate, called its half-life, which can be measured in the laboratory • This is the key to a technique called radioactive age dating, which is used to determine the ages of rocks • The oldest rocks found anywhere in the solar system are meteorites, the bits of that survive passing through the Earth’s atmosphere and land on our planet’s surface • Radioactive age-dating of meteorites, reveals that they are all nearly the same age, about 4.56 billion years old

33 Thoughtful Interlude

• “The grand aim of all science is to cover the greatest number of empirical facts by logical deduction from the smallest number of hypotheses or axioms.” »Albert Einstein, 1950

34 Solar System Origins Questions

• How did the solar system evolve? • What are the observational underpinnings? • Are there other solar systems? (to be discussed at end of semester) • What evidence is there for other solar systems? • BEGIN AT THE BEGINNING... 35 Origin of Universe Summary (a la Big Bang)

Era Epochs Main Event Time after bang The Vacuum Era Planck Quantum <10-43 sec. Inflationary Epoch fluctuation <10-10 sec. Inflation The Radiation Era Electroweak Epoch Formation of 10-10 sec. Strong Epoch leptons, bosons, 10-4 sec. Decoupling hydrogen, helium 1 sec. - 1 month and deuterium The Matter Era Galaxy Epoch Galaxy formation 1-2 billion years Stellar Epoch Stellar birth 2-15 billion years

The Degenerate Dead Star Epoch Death of stars 20-100 billion yrs. Dark Era Black Hole Epoch Black holes 100 billion - ???? engulf? 36 Abundance of the Chemical Elements

• At the start of the Stellar Era • there was about 75-90% hydrogen, 10-25% helium and 1-2% deuterium • NOTE WELL: • Abundance of the elements is often plotted on a logarithmic scale – this allows for the different elements to actually appear on the same scale as hydrogen and helium – it does show relative differences among higher atomic weight elements better than linear scale • Abundance of elements on a linear scale is very different 37 Logarithmic Plot of Abundance

Logarithmic Plot of Chemical Abundance of Elements

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100 Relative Abundance

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1 HHeCNONeMgSiSiFe38 Chemical Species A Linear View of Abundance

Linear Plot of Chemical Abundance

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40000 Relative abundance

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0 HHeCN ONeMgSiSiFe 39 Chemical Species Recall Observations

• Radioactive dating of solar system rocks – Earth ~ 4 billion years – Moon ~4.5 billion years – Meteorites ~4.6 billion years • Most orbital and rotation planes confined to plane with counterclockwise motion • Extensive satellite and rings around Jovians • Planets have more of the heavier elements than the sun

40 Planetary Summary

Mass Density Major Planet (Earth=1) (g/cm3) Constituents

Mercury 0.06 5.4 Rock, Iron Venus 0.82 5.2 Rock, Iron Earth 1.00 5.5 Rock, Iron Mars 0.11 3.9 Rock, Iron

Jupiter 318 1.3 H, He Saturn 95 0.7 H, He

Uranus 14 1.3 Ices, H, He Neptune 17 1.7 Ices, H, He

41 Other Planet Observations

• Terrestrial planets are closer to sun – Mercury – Venus – Earth – Mars • Jovian planets further from sun – Jupiter – Saturn – Uranus – Neptune 42 Some Conclusions

• Planets formed at same time as Sun • Planetary and satellite/ring systems are similar to remnants of dusty disks such as that seen about stars being born (e.g. T Tauri stars) • Planet composition dependent upon where it formed in solar system

43 Nebular Condensation (protoplanet) Model

• Most remnant heat from collapse retained near center • After sun ignites, remaining dust reaches an equilibrium temperature • Different densities of the planets are explained by condensation temperatures • Nebular dust temperature increases to center of nebula

44 Nebular Condensation Physics

• Energy absorbed per unit area from Sun = energy emitted as thermal radiator • Solar Flux = Lum (Sun) / 4 x distance2 4 • Flux emitted = constant x T [Stefan-Boltzmann] • Concluding from above yields T = constant / distance0.5

45 Nebular Condensation Chemistry

Molecule Freezing Point Distance from Center H2 10 K >100 AU

H2O273 K>10 AU

CH4 35 K >35 AU

NH3 190 K >8 AU

FeSO4 700 K >1 AU

SiO4 1000 K >0.5 AU

46 Nebular Condensation Summary

• Solid Particles collide, stick together, sink toward center – Terrestrials -> rocky – Jovians -> rocky core + ices + light gases • Coolest, most massive collect H and He • More collisions -> heating and differentiating of interior • Remnants flushed by solar wind • Evolution of atmospheres 47 iClicker Question

The most abundant chemical element in the solar nebula A Uranium BIron C Hydrogen D Helium E Lithium

48 A Pictorial View of Solar System Origins

49 Pictorial View Continued

50 HST Pictorial Evidence of Extrasolar System Formation

51 HST Pictorial Evidence of Extrasolar System Formation

52 iClicker Question

As a planetary system and its star forms the temperature in the core of the nebula A Decreases in time B Increases in time C Remains the same over time D Cannot be determined

53 iClicker Question

As a planetary system and its star forms the rate of rotation of the nebula A Decreases in time B Increases in time C Remains the same over time D Cannot be determined

54 The Sun and planets formed from a solar nebula

• According to the nebular condensation hypothesis, the solar system formed from a cloud of interstellar material sometimes called the solar nebula • This occurred 4.56 billion years ago (as determined by radioactive age-dating)

55 • The chemical composition of the solar nebula, by mass, was 98% hydrogen and helium (elements that formed shortly after the beginning of the universe) and 2% heavier elements (produced later in stars, and cast into space when stars exploded)

• The nebula flattened into a disk in which all the material orbited the center in the same direction, just as do the present-day planets 56 • The heavier material were in the form of ice and dust particles 57 • The Sun formed by gravitational contraction of the center of the nebula • After about 108 years, temperatures at the protosun’s center became high enough to ignite nuclear reactions that convert hydrogen into helium, thus forming a true star 58 59 60 The planets formed by the accretion of planetesimals and the accumulation of gases in the solar nebula

61 Chondrules

62 63 64 65 Astronomers have discovered planets orbiting other stars

• Geoff Marcy is using the 10-meter Keck telescope in Hawaii to measure the Doppler effect in stars that wobble because of planets orbiting around them • So far, he and other teams have found more than 100 extrasolar planets

66 Finding Extrasolar Planets • Doppler Shift – Of unseen companions • Photometry – Measure the light • Gravitational lensing – A GR effect

67 Extrasolar Planets

Most of the extrasolar planets discovered to date are quite massive and have orbits that are very different from planets in our solar system 68 69 iClicker Question

Mercury experiences extreme highs and lows in temperature, between day and night A Mercury is so close to the sun B because it lacks a "blanket" of atmosphere C because Mercury's atmosphere has a runaway greenhouse effect D because of Mercury's E all of the above

70 Images from Mariner 10 revealed Mercury’s heavily cratered surface

• Most of our detailed information about Mercury’s surface is from this fly-by mission in 1974/1975. • Mariner only saw one side of the planet. • There were three more planned missions to Mercury – data return began in 2009 with MESSENGER

71 iClicker Question

Mercury's surface most resembles that of A the Earth BMars C Venus D the Moon E Pluto

72 iClicker Question

The best visual (visible light) data and information on Mercury comes from A the Hubble B astronaut photographs from the Moon C spacecraft like Mariner 10 and MESSENGER D photographs from Earth based observatories E the Magellan spacecraft

73 Mercury has an iron core and a surprising magnetic field • Most iron-rich planet in the solar system with a core that is 75% of the diameter • The earth’s core is 55% of its diameter and the moon’s core is 20% of its diameter • Highest density for the planets • Weak magnetic field indicating part of the core is liquid • Magnetic field causes a magnetosphere similar to Earth’s but weaker

74 iClicker Question

Mercury has a slight magnetic field A because it rotates so quickly B because it is low in iron C which was surprising because of Mercury's slow rotation rate D because it is so close to the sun E because it’s electrically active

75 iClicker Question

Mercury's evolution as a planet is different from the Earth’s Moon A because Mercury and the Moon do not have an atmosphere B because moons and planets are fundamentally different objects C because Mercury suffered more meteoritic impacts because it's closer to the sun D because Mercury's iron core cooled and shrank, causing Mercury's surface to contract E None of the above is true, there is no difference in evolution between the two.

76 77 Venus has a hot, dense atmosphere and corrosive cloud layers

• Spacecraft measurements reveal that 96.5% of the Venusian atmosphere is carbon dioxide • Most of the balance of the atmosphere is nitrogen. • Venus’s clouds consist of droplets of concentrated sulfuric acid. • The surface pressure on Venus is 90 atm, and the surface temperature is 460°C • Both temperature and pressure decrease as altitude increases • Venus’s clouds consist of droplets of concentrated sulfuric acid • Active volcanoes on Venus may be a continual source of this sulfurous material 78 iClicker Question

Venus is very bright in the sky A due to highly reflective rocks on the surface. B due to the lightening discharges in the atmosphere. *C largely due to the highly reflective cloud cover. D due to being closer to the sun than any other planet. E because of the accumulative effects of all of the above factors.

79 The climate on Venus followed a different evolutionary path from that on Earth

• Venus’s high temperature is caused by the greenhouse effect, as the dense carbon dioxide atmosphere traps and retains energy from sunlight. • The early atmosphere of Venus contained substantial amounts of water vapor • This caused a runaway greenhouse effect that evaporated Venus’s oceans and drove carbon dioxide out of the rocks and into the atmosphere • Almost all of the water vapor was eventually lost by the action of ultraviolet radiation on the upper atmosphere. • The Earth has roughly as much carbon dioxide as Venus, but it has been dissolved in the Earth’s oceans and chemically bound into its rocks 80 iClicker Question

The Venus atmosphere A is almost completely water. B is almost completely carbon dioxide. C is almost completely nitrogen. D is almost completely oxygen. E is almost completely methane.

81 iClicker Question

The greenhouse effect on Venus has caused A little or no effect on the temperature of Venus. B the surface temperature to be much higher than what might be expected otherwise. C slow rotation rates of clouds of Venus. D the same effect on Mercury. E reduction of the surface temperature.

82 The surface of Venus shows no evidence of plate tectonics • The surface of Venus is surprisingly flat, mostly covered with gently rolling hills • There are a few major highlands and several large volcanoes • The surface of Venus shows no evidence of the motion of large crustal plates, which plays a major role in shaping the Earth’s surface

83 iClicker Question

Venus lacks a perceptible dipole magnetic field A due to the closeness to the sun. B due to the very thick atmosphere. C due to high surface temperatures. D mainly due to slow rotation E due to lack of metallic materials.

84 iClicker Question

Venus has been explored best by A spacecraft and radio observations. B spacecraft and visual (visible light) observations. C spacecraft only. D radio and visual (visible light) observations. E none of the above techniques.

85 iClicker Question

Venus may have had an ocean of water A but is all frozen at the poles of Venus now. B but it is now trapped in the subsurface of the planet. C but it was all lost to space. D which now exists as water vapor in the atmosphere. E but the water broke up into its constituents and the hydrogen escaped and the oxygen was absorbed by the surface rocks.

86 iClicker Question

Venus is hot because A of its closeness to the sun. B of its dense atmosphere. C its atmosphere is almost completely CO2. D all of the above factors are true. E None of the above.

87 iClicker Question

Venus has craters that A are all due to meteoritic impacts. B are all volcanic since no meteor penetrated the thick atmosphere. C are mostly volcanic in nature, but there are some meteoritic. D origins are not known. E are all different than any others known.

88 iClicker Question

The most information uncovered by a spacecraft about Venus was A by the Mariner spacecraft. B by the Galileo spacecraft. C by the Voyager spacecraft. D by the Viking spacecraft and its lander. E by the spacecraft Magellan using Synthetic Aperture Radar.

89 90 Mariner 4, 6 and 7

• Mariner 4 – Mars flyby mission – closest approach came on July 15, 1965 – pictures from this mission showed no canals and a surface that was disappointingly looking like that of the moon, quite LIFELESS • In 1969 the United States launched Mariner 6 (February) and Mariner 7 (March) • At closest approach (July for Mariner 6 and August for Mariner 7) both craft were at a distance of approximately 3400 kilometers 91 Mariner 4 Photograph

92 Mariners 6 and 7

• The Mariners (6 & 7) contained: – narrow and wide angle cameras – infra-red radiometer – infra-red spectrometer – ultra-violet spectrometer • Temperature, pressure and atmospheric constituents were analyzed • Pictures were still anything but spectacular 93 iClicker Question

Mars’ rotation on its axis A is similar in length to a Jupiter day. B is twice as long as a day on Earth. C is similar in length to Earth's day. D is similar in length to a Venus day. E is similar in length to a Mercury day.

94 iClicker Question

Seasons on Mars, like earth are fundamentally caused by A circular orbits. B eccentric orbits. C elliptical orbits. D the distance from the Sun. E the tilt of the rotational axis.

95 Mariner 9 Photograph

96 A Prelude to Viking

• First approved in December of 1968 for a 1973 launch • Launch date postponed due to Congressional funding cutbacks • Idea was to launch the craft in 1975 for a landing to take place on Independence Day in 1976 • Viking 1 was to be launched on August 11, 1975 but was postponed due to a malfunction • While fashioning repairs for the spacecraft, the twin unit was substituted and so Viking 2 became Viking 1 and vice versa 97 Viking Liftoff

• Viking 1 launched August 20, 1975 • Viking 2 launched September 9, 1975 • Each Viking orbiter consisted of: – television camera system – an atmospheric water detector – an infra-red thermal mapper

98 Viking Instruments

• Each Viking lander contained: – television camera system – gas chromatograph mass spectrometer – x-ray fluorescence spectrometer – seismometer – biology lab – weather station – sampler arm • Each aeroshell contained: – a retarding potential analyzer – upper-atmosphere mass spectrometer 99 Arrival at Mars

• Viking 1 arrived at Mars on June 19,1976 – took pictures to aid in the choice of a landing site for the lander • caused a delay in the landing beyond its Independence Day rendezvous • Using the latest pictures, the western slopes of Chryse Planitia were selected for the landing of Viking Lander 1

100 Another Giant Leap for Mankind

• On July 20, 1976 (seven years after a man had taken his first steps on the moon) – Viking Lander I successfully descended upon the soil of Mars • immediately after successful touchdown, the lander had instructions for taking pictures with its camera (there was actually a concern that the lander might sink into the soil, and so at least a picture was desired before it conceivably had sunken)

101 The Viking Look

• The Viking cameras – not cameras in the conventional sense – each consisted of: • a nodding mirror • a rotating turret which caused the images to be reflected down to the photodiode, which built up a picture as a series of pixels from each scan of the mirror and rotation of the turret – criticized for its inability to detect any moving objects (some still felt it possible that there might be macroscopic creatures on the planet) 102 Viking Orbiter Photograph

103 The Changing Face

104 Viking Lander Photograph

105 Reach Out and Touch

• On July 22, 1976 the sampler arm was to be deployed – however, there were difficulties • overcome by ingenious engineers • The sampler arm was finally deployed on July 28

106 First Results from Soil Sample

• X-ray fluorescence spectrometer (to determine the inorganic composition of the soil sample) – 15-30 percent silicon – 12-16 percent iron – 3-8 percent calcium – 2-7 percent aluminum

107 A Mass Disappointment

• Gas chromatograph mass spectrometer results – indication of carbon dioxide – little water – NO organic compounds • The beginning of a controversy – this negative result conflicted with results from the biology experiments

• indicative of the existence of microbial life 108 Looking for Life

• The biology laboratory – approximately a single cubic foot of volume – consisted of: • pyrolytic release experiment • labeled release experiment • gas exchange experiment

109 Pyrolytic Release Experiment

• PI was Norman Horowitz • Basis of experiment – ability of an organism to metabolize carbon dioxide and produce some product (reverse process of Levin's experiment) – soil sample placed in test chamber for five days and incubated with/without light – if soil had fixed or metabolized the carbon dioxide (carbon-14 tagged) then pyrolysis of the sample would allow detection of labeled carbon in the chamber’s gas 110 Gas Exchange Experiment

• PI was Vance Oyama • Basis of experiment – evidence of metabolism by noting changes in the gaseous environment of the sample – sample would be introduced into the chamber and the chamber's atmosphere analyzed • after a period of incubation, the gas would be re-examined and a comparison is made between this analysis and the initial analysis 111 Labeled Release Experiment

• PI was Gilbert Levin • Basis for experiment – property of microorganisms to metabolize organic compounds in a nutrient broth – organics in broth tagged with carbon 14 – If organisms in the sample were metabolizing the nutrient, the carbon-14 would appear in the chamber's gas by the appearance of tagged carbon monoxide or carbon dioxide 112 Biology Experiment Results

• All three biology experiments registered results which were indicative of some very active samples, and if these results were obtained on earth there would be no doubt that organisms were responsible • Doubt of the biological results once the GCMS had failed to detect any organics within the soil sample

113 Explaining Biology Away

• Theories dealing with superoxides, peroxides and superperoxides to explain apparent positive results away the results of • Only hold-out for the possibility that the biology experiments still might indicate the existence of life on Mars was Gilbert Levin [only science team member that still maintains belief that evidence of life was found] 114 Levin’s View Today

• “After 25 years, the Mars LR data still excite attempts at a chemical explanation, three within the last year. This indicates that none of the 30 non-biological explanations offered to date has been completely convincing. New findings concerning the existence of liquid water on the surface of Mars, and extremophile microorganisms on Earth, are consistent with my conclusion that the LR detected living microorganisms in the soil of Mars (Levin 1997), which may explain the difficulties with the non- biological theories.”

115 Viking’s View of Atmosphere

• Viking Lander meteorological instruments – at end of boom that deployed after landing • contained thermocouple units to measure the atmospheric temperature and wind speed – an atmospheric pressure sensor which was not on the boom so as to be shielded from winds

116 First Mars Weather Report

• Seymour Hess stated: – "Light winds from the east in the late afternoon, changing to light winds from the southwest after midnight. Maximum winds were 15 miles per hour. Temperature ranged from minus 122 degrees Fahrenheit just after dawn to minus 22 degrees Fahrenheit. Pressure steady at 7.7 millibars."

117 Viking Looks at Climate

• Long term data available –from Viking Lander 1 through Novermber 5, 1982 –from Viking Lander 2 through April 11, 1980

118 Viking Climate Conclusions

• discovered nature of surface pressure variations over the seasons and the cycling of the atmosphere between the polar caps – minimum in the pressure cycle occurs during the southern winter when the carbon dioxide mass condensing onto the south polar cap is a maximum – as the seasonal carbon dioxide sublimes out of the south polar cap, the pressure rises until the north polar cap starts to form – process reverses seasonally and carbon dioxide reforms at the south polar cap 119 A Little Mars Geology

• Viking Orbiter images – largest volcano in solar system, Olympus Mons – large canyon, Valles Marineris – a global appearance roughly organized latitudinally • equatorial belt is somewhat darker than the mean albedo and very changeable over time • northern and southern mid-latitude regions are brighter, due probably to the deposits of very fine, bright material • a dark collar around the north polar region • polar regions with the very bright polar caps

120 More Beautiful Pictures

• High resolution images from Viking Orbiters – contributed to better understanding the surface – indication that the darker areas are where the silicates are somewhat more reduced and richer in ferrous rather than ferric silicates – areas that were originally considered for landing were found to be too hilly – surprised to find that the Lander was actually in a field strewn with rocks (e.g. Little Joe) large enough so that if the Lander had landed on one of them the mission would have failed 121 iClicker Question

Mars possesses shield volcanoes believed to A have never erupted. B be formed by plate tectonics. C be smaller than those on Earth. D be currently active. E be caused by an ancient hot spot in the mantle.

122 iClicker Question

Among the following, which discovered the most information about Mars? A The Pioneer spacecraft. B The Galileo spacecraft. C The Voyager spacecraft. D The Viking spacecraft and its lander. E The spacecraft Magellan using Synthetic Aperture Radar.

123 iClicker Question

Mars' two moons, probably captured asteroids, are called A Valles and Marineris. B Phobos and Deimos. C Chryse and Planitia. D Olympus and Mons. E Romulus and Remus.

124 iClicker Question

Mars has outflow channels A probably caused by rainfall. B probably caused by catastrophic flooding. C probably caused by the melting of the ice caps. D probably caused by the water comets impacting the surface. E probably caused by the surface winds.

125 iClicker Question

Part of the Martian surface is higher in altitude and has a higher crater density. This tells us that A dust storms destroyed the surface of Mars in other regions. B sulfuric acid rain destroyed the surface of Mars. C this surface is older and has not seen the erosion that other portions experienced. D volcanic ash is a form of grounded up rock. E the atmosphere was denser and of different composition in that region.

126 iClicker Question

Mars volcanoes are generally higher above the surface than Earth's volcanoes because A its material is less dense than Earth rock. B it has a thin crust. C it has a thick crust. D it is further from the Sun. E largely because of lower gravity.

127 iClicker Question

Ultimately, Viking's search for life A gave no definitive answer as to the existence of life on Mars. B proved that there was life on Mars. C proved that there was no life on Mars. D proved that there was no organic life on Mars. E discovered microscopic life remains in the rocks.

128 Meteorite from Mars

• ALH84001 – possible evidence of fossil microbes from Mars

129 Simplified Conclusions re Mars

• Did Viking find life on Mars? – Nope, but it’s considered uncertain and controversial • Did Viking find ruins of an ancient civilization? – Nope • Does ALH84001 contain microfossils? – Nope • Do we know that there is no life on Mars? – Nope 130 131 132 Jupiter and Saturn are the most massive planets in the solar system

• Jupiter and Saturn are both much larger than Earth • Each is composed of 71% hydrogen, 24% helium, and 5% all other elements by mass • Both planets have a higher percentage of heavy elements than does the Sun • Jupiter and Saturn both rotate so rapidly that the planets are noticeably flattened

133 Atmospheres

• The visible “surfaces” of Jupiter and Saturn are actually the tops of their clouds • The rapid rotation of the planets twists the clouds into dark belts and light zones that run parallel to the equator • The outer layers of both planets’ atmospheres show differential rotation – The equatorial regions rotate slightly faster than the polar regions • For both Jupiter and Saturn, the polar rotation rate is nearly the same as the internal rotation rate

134 iClicker Question

• Saturn's density is A higher than Jupiter's density. B highest of the gas giants. C lowest because of its mass. D is lowest because of its gravity. E so low you could float it in water.

135 iClicker Question

• and 2 made major discoveries about Jupiter including A the fact that Jupiter has a ring. B the fact that Jupiter's red spot has complex eddies, like a hurricane on Earth. C the fact that Jupiter's moons are as varied as the planets themselves. D All of the above. E None of the above

136 137 iClicker Question

• Saturn gives off more heat than it absorbs A because of its enormous mass. B because its methane is a greenhouse gass. C because its thick clouds contribute to heat generation. D because of helium rain that gives off heat as it falls to center. E because it is radiating heat left over from its formation.

138 iClicker Question

• Saturn has oval storm systems and turbulent flow patterns A powered by the greenhouse effect. B powered by convection and rapid rotation. C powered by liquid hydrogen. D powered by metallic hydrogen rotating at high velocity. E powered by the rings of Saturn.

139 The oblateness of Jupiter and Saturn reveals their rocky cores • Jupiter probably has a rocky core several times more massive than the Earth • The core is surrounded by a layer of liquid “ices” (water, ammonia, methane, and associated compounds) • On top of this is a layer of helium and liquid metallic hydrogen and an outermost layer composed primarily of ordinary hydrogen and helium • Saturn’s internal structure is similar to that of Jupiter, but its core makes up a larger fraction of its volume and its liquid metallic hydrogen mantle is shallower than that of Jupiter 140 iClicker Question

Jupiter is noticeably oblate A mainly because of its strong magnetic field. B mainly because of its distance from the Sun. C mainly because of rapid rotation. D mainly because of the tidal effects of its moons. E mainly because of its large mass.

141 iClicker Question

• Jupiter emits more energy than it absorbs A due to the helium rain falling in. B due to the escape of gravitational energy released during its formation. C due to the decay of radioactive elements. D due to a small amount of fusion in its core. E due to the generation of heat from tidal forces.

142 iClicker Question

Jupiter is believed to have a massive core A where fusion takes place. B consisting of liquid hydrogen. C consisting of gaseous hydrogen and helium. D consisting of metallic hydrogen. E consisting of rocky material.

143 Metallic hydrogen inside Jupiter and Saturn endows the planets with strong magnetic fields

• Jupiter and Saturn have strong magnetic fields created by currents in the metallic hydrogen layer • Jupiter’s huge magnetosphere contains a vast current sheet of electrically charged particles • Saturn’s magnetic field and magnetosphere are much less extensive than Jupiter’s

144 iClicker Question

Jupiter emits radio waves A caused by charged particles moving in its magnetic field. B caused by metallic hydrogen in the mantle. C massive gravitational forces. D caused by the Great Red Spot. E large Coriolis forces on the atmosphere.

145 iClicker Question

• Saturn has a magnetic field A caused by rapid rotation of methane clouds. B caused by rapid rotation of nitrogen clouds. C caused by rapid rotation of metallic hydrogen. D caused by rapid rotation of molecular hydrogen. E caused by rapid rotation of water ice.

146 • The principal rings of Saturn are composed of numerous particles of ice and ice-coated rock ranging in size from a few micrometers to about 10 m • Jupiter’s faint rings are composed of a relatively small amount of small, dark, rocky particles that reflect very little light • Most of its rings exist inside the Roche limit of Saturn, where disruptive tidal forces are stronger than the gravitational forces attracting the ring particles to each other • Each of Saturn’s major rings is composed of a great many narrow ringlets

147 iClicker Question

• The rings of Saturn A are solid rings around Saturn. B lie within the Roche limit of Saturn. C lie outside the Roche limit of Saturn. D lie precisely at the Roche limit of Saturn. E are not visible from Earth-bound telescopes.

148 iClicker Question

• Saturn's famous rings are A composed of complex carbohydrates. B composed of a solid thin disk of material. C composed mostly of rocky boulders. D composed of a disk of liquid helium. E composed mostly of icy particles moving about Saturn.

149 iClicker Question

• The Roche limit is an important concept A that defines the maximum brightness a moon be be. B that defines the maximum mass a moon can possess. C that defines the maximum density of a planets' ring system. D that defines the critical distance from a planet inside of which a moon can be tidally destroyed. E that defines the critical distance from a planet to its moon. 150 Jupiter’s Galilean satellites are easily seen with Earth-based telescopes

• The four Galilean satellites orbit Jupiter in the plane of its equator • All are in synchronous rotation • The orbital periods of the three innermost Galilean satellites, Io, Europa, and Ganymede, are in the ratio 1:2:4

151 • The two innermost Galilean satellites, Io and Europa, have roughly the same size and density as our Moon • They are composed principally of rocky material • The two outermost Galilean satellites, Ganymede and Callisto, are roughly the size of Mercury • Lower in density than either the Moon or Mercury, they are made of roughly equal parts ice and rock 152 iClicker Question

• The largest Jupiter moon is AIo. B Europa. C Callisto. D Ganymede. E Almathea.

153 Io is covered with colorful sulfur compounds ejected from active volcanoes

154 Tidal Heating

• The energy to heat Io’s interior and produce the satellite’s volcanic activity comes from tidal forces that flex the satellite • This tidal flexing is aided by the 1:2:4 ratio of orbital periods among the inner three Galilean satellites

155 iClicker Question

• The most geologically active moon is AIo. B Ganymede. C Europa. D Callisto. E Almathea.

156 iClicker Question

• Volcanic activity on the geologically active moon of Jupiter is caused by A Jupiter's enormous mass. B tidal stresses from Jupiter alone. C tidal stresses from all other moons. D tidal stresses from Jupiter and Europa. E Jupiter's enormous gravity.

157 Europa is covered with a smooth layer of ice that may cover a worldwide ocean

• While composed primarily of rock, Europa is covered with a smooth layer of water ice

• The surface has hardly any craters, indicating a geologically active history

• As for Io, tidal heating is responsible for Europa’s internal heat

• Minerals dissolved in this ocean may explain Europa’s induced magnetic field

158 Liquid water may also lie beneath the cratered surfaces of Ganymede and Callisto

159 iClicker Question

• In general what can be said about Jupiter's moons? A That all the moons were formed with Jupiter. B That some formed with Jupiter and some were captured. C That all the moons were captured by Jupiter. D That some moons formed in the inner solar system. E That all the moons are larger that the terrestrial planets.

160 Titan has a thick, opaque atmosphere rich in methane, nitrogen, and hydrocarbons

• The largest Saturnian satellite, Titan, is a terrestrial world with a dense nitrogen atmosphere • A variety of hydrocarbons are produced there by the interaction of sunlight with methane • These compounds form an aerosol layer in Titan’s atmosphere and possibly cover some of its surface with lakes of ethane

161 iClicker Question

• Saturn's moon Titan is most interesting A because it possess an atmosphere like that of today's Earth. B because it possesses a thick atmosphere that may be like primordial Earth's atmosphere. C because it has ice volcanism. D because it is a large moon. E because it demonstrates the Roche critical limit.

162 iClicker Question

• Titan's atmosphere A consists mostly of hydrogen. B consists mostly of carbon dioxide. C consists mostly of sulfur. D consists mostly of methane. E consists mostly of nitrogen.

163 iClicker Question

• Saturn has shepherd moons A named for the astronaut Alan Shepherd. B that even the Voyager spacecraft could not detect. C that are small moons which confine a narrow ring. D that are moons that are outside the Roche limit. E that are moons that orbit larger moons.

164 iClicker Question

• Most of Saturn's moons and Jupiter's moons A are smaller than the moons of Mars. B are orbiting erratically. C are larger than the terrestrial planets. D are near the critical Roche distance. E are tidally locked by gravity into synchronous rotation.

165 166 167 168 Uranus was discovered by chance, but Neptune’s existence was predicted by applying Newtonian mechanics • Uranus recognized as a planet in 1781 by William Herschel • Neptune’s position calculated in mid- 1840’s because of slight deviations in Uranus’ orbit • Credit shared by Le Verrier and Adams

169 Uranus is nearly featureless and has an unusually tilted axis of rotation

• Both Uranus and Neptune have atmospheres composed primarily of hydrogen, helium, and a few percent methane • Methane absorbs red light, giving Uranus and Neptune their greenish-blue color

Neptune is a cold, bluish world with Jupiter like atmospheric features

• No white ammonia clouds are seen on Uranus or Neptune • Presumably the low temperatures have caused almost all the ammonia to precipitate into the interiors of the planets • All of these planets’ clouds are composed of methane • • Much more cloud activity is seen on Neptune than on Uranus. • This is because Uranus lacks a substantial internal heat source.

170 Uranus and Neptune contain a higher proportion of heavy elements than Jupiter and Saturn

• Both Uranus and Neptune may have a rocky core surrounded by a mantle of water and ammonia • Electric currents in the mantles may generate the magnetic fields of the planets 171 Uranus and Neptune each have a system of thin, dark rings

172 Triton is a frigid, icy world with a young surface and a tenuous atmosphere • Neptune has 13 satellites, one of which (Triton) is comparable in size to our Moon or the Galilean satellites of Jupiter • Triton has a young, icy surface indicative of tectonic activity • The energy for this activity may have been provided by tidal heating that occurred when Triton was captured by Neptune’s gravity into a retrograde orbit • Triton has a tenuous nitrogen atmosphere 173 Pluto Statistics

• Orbital semi-major axis => 39.48 AU – Perihelion => 29.66 AU – Aphelion => 49.31 AU • => 0.249 • Mean orbital speed => 4.74 km/s • Sidereal => 249 Earth years • Orbital inclination to ecliptic => 17.150

174 Pluto Stats (cont’d) • Mass => 1.27 x 1022 kg (0.0021 Earth mass) • Equatorial radius => 1137 km – 0.18 Earth radius • Mean density => 2.06 g/cc 2 • Surface gravity => 0.66 m/s (1.2 km/s escape velocity) • => 6.4 days “retrograde” • Axis tilt => 1180 • Surface Temp => 40-60 K

175 Pluto Surprises

• It has moons • Original moon discovered 1978 – Charon (KAIR’ en) • Now more – 2005 discovery of 2 additional moons – Named Nix and Hydra 176 Pluto’s History • Planet X predicted – from perturbations in Uranus and Neptune orbit • Discovered February 18, 1930 – discovered by Clyde Tombaugh • accidental discovery (Neptune’s mass was wrong) • First moon discovered 1978 (announced 7 July) – discovered by James Christy • Spectroscopic studies – First attempt in ‘30s, first success in ‘70s

177 Spectral Analysis

• Compare with known samples • First conclusions – methane ice – water ice – ammonia ice • Develop models for surface to interior – based upon spectral analyses and density

178 Pluto’s Interior to Surface Model

• Model 1 – partially hydrated rock core – water ice layer II – predominant water ice layer I • Model 2 – partially hydrated rock core – organics layer – predominantly water ice layer

179 Finding Charon

• Look at the light – light curves indicative of eclipsing binary • similar to light curves of binary stars – learn more about these in ASTR 113 • Look at details of photographs – “bump” on Pluto image

180 All about Charon

• Best images from Hubble Space Telescope – highest angular separation (resolution)

181 A Binary Like Earth?

• Size of Pluto compared to Charon – Some call it “binary planet” • What is origin of Charon • Situation is similar to Earth and Moon – some consider Earth-Moon a binary planet • Moon was formed from Earth

182 iClicker Question

Pluto should not be referred to as a Jovian planet because A it is more like a terrestrial planet. B it has no rings. C it is more like an icy moon. D it contains no hydrogen, only helium. E it's not a planet, but an asteroid.

183 iClicker Question

How can we know the composition of the atmosphere of Pluto? A We cannot know, it is all just a theory. B We can use spectral analysis. C We can use pyschokinesis. D We sent a spacecraft to Pluto. E We use gravitational perturbations.

184 iClicker Question

Pluto's surface and interior A consists of partially hydrated rock, organics and water ice. B consists of partially hydrated rock and layers of water ice. C either A or B above are feasible. D can never be determined. E cannot be determined until we land on Pluto.

185 iClicker Question

In terms of size and mass, Pluto is most similar to which of the following: AIo B Titan C Phobos D Deimos ETriton

186 Definition of Comet

• Comet [according to Funk and Wagnalls Standard Desk Dictionary] - “A celestial body moving in an orbit about the sun and consisting of a nucleus of more or less condensed material, accompanied by a tenuous coma pointing away from the sun.”

187 Definition of Asteroid

• Asteroid [according to Funk and Wagnalls Standard Desk Dictionary] - “Any of several hundred small planets between Mars and Jupiter; also called planetoid.”

188 Definition of Meteor

• Meteor [according to Funk and Wagnalls Standard Desk Dictionary] - “A meteoroid that on entering the earth’s atmosphere at great speed is heated to luminosity and is visible as a streak of light; also called a shooting star.”

189 Definition of Meteoroid

• Meteoroid [according to Funk and Wagnalls Standard Desk Dictionary] - “One of the pieces of matter moving through outer space, that upon entering the earth’s atmosphere form meteors.”

190 Definition of Meteorite

• Meteorite [according to Funk and Wagnalls Standard Desk Dictionary] - “A portion of a meteor that has not been completely destroyed by combustion and has fallen to earth.”

191 Misconceptions about things that go boom

• [Adapted from David Levy’s book Comets: Creators and Destroyers] • 1 - It can’t happen to us. Things won’t change after a major impact. • 2 - Any object that hits the Earth could cause global devastation. • 3 - To prevent an impact, we have to destroy the comet or asteroid.

192 [Adapted from David Levy’s book Comets: Creators and Destroyers] Misconceptions about things that go boom

• 4 - The chance that a comet or asteroid that could damage the Earth’s ecosystem will land in our lifetime is virtually zero. • 5 - Earth is just as much at risk now as it was in the past. • 6 - Impacts are bad for life. • 7 - Every mass extinction was caused by an impact.

193 [Adapted from David Levy’s book Comets: Creators and Destroyers] Misconceptions about things that go boom

• 8 - An object the size of the dinosaur comet cannot threaten the Earth today. • 9 - Life began on comets. • 10 - Impacts are science fiction; they don’t really happen in the solar system.

194 [Adapted from David Levy’s book Comets: Creators and Destroyers] Picture an Asteroid (Gaspara by Galileo)

[Source: Dr. Sten Odenwald 195 Astronomy Café] Picture a Comet (Halley’s by Giotto)

[Source: Dr. Sten Odenwald 196 Astronomy Café] Where did they come from?

• Kuiper Belt – Just beyond reaches of solar system, once thought to be location of origin of comets. – Likely source of “Jupiter family short-period comets.” • – Likely region of most comets, located far away from solar system (25,000 - 100,000 AU). – These comets were likely formed closer in, but their orbits were influenced by the Jovian planets. – Possible location of a Brown Dwarf (Matese, 1999).

197 Damage From Space

Yield Asteroid Crater Diameter (megatons Effect Size (kilometers) TNT) Land impacts destroy major metropolitan area, e.g. Washington, D,C 75 meters 100 1.5 or Paris Destroys area the size of a small state. Ocean impact produce 350 meters 5000 6.0 tsunamis. Land impact destroys areas the size of Virginia or Tiawan, and 700 meters 15,000 12.0 ocean impact produces major tsunami 1.7 Land impact affects climate, ozone and tsunamis destroy coastal 200,000 30.0 kilometers conununities. 3.0 Large nation destroyed. Widespread fires from ejecta. Major climate 1 million 60.0 kilometers change. 7.0 50 million 125 Mass extinction, global conflagration and long term climate change. kilometers

[Source: Dr. Sten Odenwald, Astronomy Café]198 What Determines the Hazard

• Impactor flux (quantity, how destabilized) • Fatalities determined by damaged target – high density population centers – oceans - can cause catastrophic tsunamis • Damage determined by energy • Energy equals (1/2) (mass) (velocity2) • Mass determined by density / composition • Velocity determined by orbit – long-period, short-period 199 [Copyright (c) 1999 Richard P. Binzel, Massachusetts Institute of Technology. Permission is hereby granted to reproduce Torino Scale figures and text for educational and news reporting purposes.]

200 Predicted Close Calls Between now and 2004 AD: Asteroid Distance Date Close Calls (?) (kilometers) 1863 Antinous 565,000 April 1999 2340 Hathor 838,000 October 2086 1999 XF11 937,000 October 2028 2340 Hathor 970,000 October 2069 1991 JX 980,000 June 1999 2101 Adonis 1,060,000 February 2177 1986 PA 1,064,000 April 2001 1980 WF 1,155,000 January 2001 4660 Nereus 1,180,000 February 2060 1992 FE 1,218,000 March 2000 3362 Khufu 1,288,000 January 2001 4179 Toutatis 1,530,000 September 2004 4581 Asclepius 1,800,000 March 2051 2100 Ra-Shalom 2,114,000 September 2000 4660 Nereus 2,200,000 February 2071 1990 OA 2,200,000 July 2070 3361 Orpheus 2,450,000 April 2194 4183 Cuno 3,390,000 June 1998 4179 Toutatis 3,640,000 September 2004 1990 Os 8,750,000 November 2003 Observed Recent Close Calls: Asteroid Distance Date Size (kilometers) 1994 XM1 102,900 12-9-1994 9 meters 1993 KA2 147,000 5-20-1993 6 1994 ES1 162,000 3-15-1994 7 1991 BA 160,000 1-18-1991 7 [Source: Dr. Sten Odenwald 1995 FF 426,000 5-27-1995 18 Astronomy Café] 1996 JA1 440,000 5-19-1996 220 4581 Asclepius 676,000 3-22-1989 280 1994 WRI2 705,000 11-24-1994 140 1937 Hermes 720,000 10-30-1937 900 201 The Earth-Moon distance is 350,000 kilometers or 224,000 miles for comparison Coming to a Theater Near You

Quadrantids...... January 2- 4...... 30 Lyrids...... April 20 - 22...... 8 Eta Aquarids...... May 2 - 7...... 10 Delta Aquarids...... July 20 to August 14.....15 Perseids...... July 29 to August 18.....40 Draconids...... Oct 10...... ? Orionids...... Oct 17-24...... 15 Taurids...... Oct 20 to Nov 25...... 8 Leonids...... Nov 14-19 ...... 6 Andromedids...... Nov 15 to Dec 6...... ? Geminids...... Dec 8 - 15...... 50 Ursids...... Dec 19 - 22...... 12 Ariertids...... May 29 - June 17...... 40 Zeta Perseids...... June 1-15...... 30 Beta Taurids...... June 23 - July 7...... 20

[Source: Dr. Sten Odenwald, Astronomy202 Café] Shoemaker-Levy 9

• Cometary impact on Jupiter – Changed views about possibilities of such an impact on Earth

203 iClicker Question

Which of the following is true of comets and asteroids? A Earth is just as much at risk now, of an impact, as it was in the distant past. B All impacts are detrimental to life. C Every mass extinction on Earth was caused by an impact. D All of the above. E None of the above.

204 iClicker Question

Which of the following meteor showers are linked to cometary debris? A Orionids B Leonids C Geminids D All of the above. E None of the above.

205 iClicker Question

The orbits of most asteroids A lie beyond the orbit of Mars. B cross the orbit of Mars. C lie beyond the orbit of Jupiter. D cross the orbit of Earth. E bring them near the Sun.

206 A Quick Review of Asteroids

• Categorized as family of objects – between the orbits of Mars and Jupiter – can be in other inner solar system orbits • A part of our solar system • Can go boom if you bump into them • Of interest in study of primordial stuff – inner solar system stuff, rocky material – have been found with satellites of their own 207 A Quick Review of Comets

• Observed by humans for generations • Originally considered as signs of bad fate • The source of common meteor showers • A part of the solar system • Kuiper Belt and Oort Cloud parking lots • Can cause a “boom” in the night (or day) • Of interest for primordial matter studies

208 iClicker Question

Comets are thought to reside mainly in A the inner solar system. B an orbit between Mars and Jupiter. C the solar nebula. D an orbit parallel to Earth. E the Oort Cloud and Kuiper Belt.

209 iClicker Question

Comets are made of A silicates. B dust particles. C methane, ammonia and water ice. D all of the above. E None of the above.

210 iClicker Question

Meteor showers are caused by A a small constellation of dying stars, called shooting stars. B Earth crossing the orbit of a comet's debris. C Earth crossing the orbit of the . D Earth crossing the orbit of an asteroid. E a large number of iron filings.

211 iClicker Question

The Oort Cloud is considered to be A a cloud of debris between Mars and Jupiter. B a cloud of comets surrounding the solar system. C a cloud of comets near Pluto. D a cloud of comets in the inner solar system. E a cloud of comets in the Jovian neighborhood.

212 iClicker Question

Trojan asteroids A have orbits that cross the orbit of the Earth. B have orbits within the Kuiper Belt. C have orbits within the Oort Cloud. D have orbits at a distance of Jupiter. E have orbits like runaway comets.

213 iClicker Question

What part of a comet has only been seen with the aid of a spacecraft? AComa B Dust tail C Nucleus D Ion tail E Hydrogen envelope

214 Jargon I

• asteroid • kinetic energy • asteroid belt • Kuiper belt • average density • Kuiper belt objects • chemical composition • liquid metallic hydrogen • comet • magnetometer • dynamo • meteoroid • escape speed • • ices • molecule • impact crater • spectroscopy • Jovian planet • terrestrial planet

215 Jargon II

• accretion • meteorite • astrometric method • nebulosity • atomic number • nebular hypothesis • brown dwarf • Oort cloud • center of mass • planetesimal • chemical differentiation • protoplanet • chondrule • protoplanetary disk (proplyd) • condensation temperature • protosun • conservation of angular • radial velocity method momentum • radioactive age-dating • core accretion model • radioactive decay • disk instability model • solar nebula • extrasolar planet • solar wind • half-life • T Tauri wind • interstellar medium • transit • jets • transit method • Kelvin-Helmholtz contraction 216