lecture 31: the family of the sun astronomy 161 – winter 2004
TRANSCRIPT
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Lecture 31:
The Family of the Sun
Astronomy 161 – Winter 2004
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Key Ideas:The Solar System contains:
• The Sun• Terrestrial Planets• Jovian Planets• Pluto• Giant Moons• Asteroids, Icy Bodies, Comets, & Meteoroids
The planets all lie in nearly the same plane and orbit in the same general direction.
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The Golden Age of ExplorationThe Solar System has been explored with robotic
spacecraft & astronauts:• Landed men on the Moon• Robotic landers on Moon, Venus, & Mars• Returned rocks from the Moon (~382 kg)• Probed Atmospheres of Venus, Mars, & Jupiter• Flown spacecraft by all planets except Pluto• Mapped Venus with radar• Flown by asteroids & comets, landing on one
asteroid
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Magellan Venus
Cassini & Huygens Mars SojournerPioneer 10 & 11
Voyager 1 & 2
Apollo 11-17
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The Family of the SunThe Sun: a middle-aged, average sized starThe Terrestrial Planets:
• Rocky Planets: Mercury, Venus, Earth & Mars
The Jovian Planets:• Gas Giants: Jupiter, Saturn, Uranus & Neptune
Pluto: fits into neither categorySmall Icy & Rocky Bodies:
• Icy: Icy Moons, Kuiper Belt Objects, & Comets• Rocky: Giant Moons, Asteroids & Meteoroids
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The 9 Planets, in order:Planets:MercuryVenusEarthMarsJupiterSaturnUranusNeptunePluto
Mnemonic:My Very Educated Mother Just Served Us Nine Pizzas
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Relative Sizes of the Planets
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Basic Properties of the PlanetsLocations:
• Terrestrial in the inner solar system: 0.4-1.5AU• Jovian in the outer solar system: 5-30 AU
All orbit in the same direction & same plane:• Orbit counterclockwise, in the same sense as the
rotation of the Sun.• All except Pluto orbit very near the Ecliptic plane.
Provides clues to Solar System formation.
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Pluto
Neptune
Uranus
Saturn
Jupiter
Mars
EarthVenus
Mercury
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Pluto
EclipticPlane
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The Solar System, by mass
The contents of the Solar System, ordered by their total mass in Earth masses:• Sun: 330,000 MEarth
• 4 Jovian Planets: 447 MEarth total
• 4 Terrestrial Planets: 1.985 MEarth total
• Giant Moons: 0.105 MEarth total
• Pluto, the icy oddball planet: 0.002 MEarth
Rest of the contents make a tiny contribution.
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The SunThe Sun is a middle-aged, average-sized star.
• Mostly Hydrogen & Helium• Contains 99.8% the mass of the Solar System• about 4.6 Gyr old
The Sun shines because it is hot:• Surface (photosphere) is ~6000 K• Radiates mostly Visible light plus UV & IR
Kept hot by nuclear fusion in its core:• Builds Helium from Hydrogen fusion.
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The Jovian Planets
Jupiter, Saturn, Uranus & Neptune• Largest Planets: at least 15 times mass of Earth.• Jupiter, largest, is 318 Earth Masses• Only in the outer solar system (5 to 30 AU)
Gas Giants (“Jupiter-like”):• No Solid Surfaces (mostly atmosphere)• Mostly Hydrogen & Helium• Rocky/icy inner cores• Low density: 0.7 to 1.7 g/cc (water is 1 g/cc)
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The Jovian Planets
Jupiter(318 M)
Uranus(15 M)
Saturn(95 M)
Neptune(17 M)
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Terrestrial Planets
Mercury, Venus, Earth & Mars• “Earth-Like” Rocky Planets• Largest is Earth• Only in the inner solar system (0.4 to 1.5 AU)
Rocky Planets:• Solid Surfaces• Mostly silicates and iron • High Density: 3.9-5.5 g/cc (rock & metal)• Earth, Venus, & Mars have atmospheres
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The Terrestrial Planets
Earth(1 M)
Mars(0.11 M)Venus
(0.82 M)
Mercury(0.055 M)
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Solid inner core
Liquid outer core
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The Giant MoonsNatural satellites orbiting planets.Giant Moons:
• Earth: The Moon• Jupiter: Io, Europa, Ganymede, & Callisto (the
Galilean moons) • Saturn: Titan • Neptune: Triton
Many smaller moons, both rocky & icy.Only Mercury & Venus have no moons.
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The Giant Moons
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Pluto: The Planet that Doesn’t Fit
Pluto is neither a Terrestrial nor Jovian Planet.• Smallest of the planets• Intermediate Density: 1.8 g/cc (mostly icy)
Pluto’s orbit is also odd:• The most elliptical orbit of all the planets• The most highly inclined: ~17º from the Ecliptic.
Largest of a distinct class of objects, but still a “planet”.
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Distant Pluto
Pluto
CharonPluto’s Moon
Hubble Reconstruction of Pluto
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Small Icy Bodies
Pluto is the largest of a class of icy bodies:• Found only in the outer solar system• Densities of 1.2 to 2 g/cc (like ices)
Examples:• Triton, large moon of Neptune• Charon, Pluto’s large moon• Trans-Neptunian Objects (Kuiper Belt Objects &
Plutinos)
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Triton
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The Leftovers (Minor Bodies)Asteroids:
• Range from 500km (Ceres) to large boulders• Made of rock (density 2-3 g/cc)
Meteoroids:• Bits of rock and metal• Range in size from grains of sand to boulders
Comets:• Composite rock & ice “dirty snowballs”• Longs tails of gas & dust are swept off them when
they pass near the Sun.
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Asteroids
253 Mathilde
951 Gaspra243 Ida
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Meteor burning up in the atmosphere.
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Comet Hale-Bopp
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5 kmNucleus of Comet Halley