Download The Solar System - School of Physics

GENS4001 Astronomy
Part 1:
The Solar System
Dr Michael Burton
Department of Astrophysics
School of Physics, UNSW
GENS4001
The Solar System
1
Overview
• 1 Star (the Sun)
• 8 + 1 Planets
– Mercury, Venus, Earth, Mars
– Jupiter, Saturn, Uranus, Neptune
– Pluto / Charon
• ≥ 61 Moons
• 100,000 (?) Asteroids, 100 million (?)
Comets, Solar Wind
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The Solar System
2
Formation of the Solar System
• Collapse of cloud of gas, dust & ice
– 4.6 billion years ago,
– Swirling, disk-shaped,
– Sun formed at centre of ‘Solar Nebula’.
• Inner planets form through accretion of dust
particles to planitesimals into protoplanets.
– Collisions & cratering dominate for 150 Myrs.
• Outer planets form through accretion of gas
onto rocky protoplanetary cores.
Our Star, the Sun
• Giant ball of plasma undergoing
thermonuclear fusion of hydrogen in centre!
• Photosphere - visible surface at 6000°C
• Chromosphere
– Jets of gas (spicules) rise along along
boundaries of granules.
• Corona - tenuous, hot (2,000,000°C) gas
– Blends into Solar Wind
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The Solar System
4
The Sun (continued)
• Surface features vary with 11-year cycle:
– Sunspots: cooler with strong magnetic field,
– Solar flare: eruption from sunspot group,
– Convection cells, transporting energy outwards.
• Energy produced by thermonuclear fusion
of 4 H-atoms into He-atom at 8 million °C.
• Solar Model well understood:
– Fusion in core about 1/4 solar radius in size,
– Neutrinos - 1/4 predicted number?
Earth / Moon
• Double planet system, tidally interacting.
• Plate Tectonics produces continents, oceans,
mountains & volcanoes.
• Iron rich core producing magnetic field.
• Atmosphere of 80% nitrogen, 20% oxygen
– Troposphere, stratosphere, mesosphere,
thermosphere
• Supports life on land, oceans & atmosphere.
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The Solar System
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Earth / Moon (continued)
• Magnetosphere surrounding Earth,
protecting atmosphere from Solar Wind.
• Collision-ejection with giant asteroid, with
debris coalescing to form Moon.
• Weathering has erased asteroid impacts on
Earth but past history still visible on Moon.
– Cratered highlands,
– Smooth-surfaced Maria, from lava flows.
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The Solar System
7
Earth / Moon Phenomena
• Phases of the Moon
– Orbit about Earth, and Solar illumination.
• Eclipses when Sun/Earth/Moon in line:
– Lunar eclipses
– Solar eclipses (inc. annular)
• Tides
– Differential gravitational pull of near and far
sides of Earth by Moon
• Asteroid collisions and mass extinctions?
What if the Moon didn’t exist?
• Effect on culture (romances)?
• No eclipses or phases - dark skies!
• Tides only 1/3 current size (from Sun).
– 12 hour cycle, constant level.
• Day would still be 6 hours long
– Enormous tides helped form soup for life?
– More powerful winds, mountains eroded.
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The Solar System
9
The Inner and Outer Planets
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Small (<13,000 km)
Rocky (iron core)
Thin atmospheres
Slow rotation
Short years
Few moons
Warm
No Rings
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Large (>50,000 km)
Gaseous (H, He)
Thick atmospheres
Rapid rotation
Long years
Many moons
Cold
Rings
The Solar System
10
Mars
• No canals, but ancient river channels!
• No plate tectonics, resulting in giant shield
volcanoes over hot spots, plus canyons.
• A few impact craters.
• Thin carbon dioxide atmosphere & red dust.
• Water must once have flowed - flash floods.
• Could life have once existed?
• 2 tiny moons (Phobos, & Deimos) are
Jupiter
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The Giant of the planets (not a failed star).
Rapid, differential rotation.
Belts & Zones, methane & ammonia clouds.
Cyclones interface: Red Spot & white ovals.
Strong magnetic fields, huge aurorae.
Gas / Liquid Metallic H / Rocky Core.
Thin, transient dust ring - meteor impacts.
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The Solar System
12
Moons of Jupiter
• 16 Moons with 4 giants (Galilean satellites).
• Io: Volcanic, sulphur-covered, kept molten
through tidal heating.
• Europa: covered in ice with intricate pattern
of cracks
– tidal heating supports oceans, life??
• Ganymede: Rock & Ice, past tectonics.
• Callisto: Rock, cratered terrain (impacts).
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The Solar System
13
Comets and Asteroids
• Debris from formation of Solar System.
• Asteroids: lumps of rock a few km in size
– Most in belt between Mars & Jupiter.
• Comets: dirty snowballs of ices and rocks
– Primordial, but transient,
– Highly elliptical orbits, from Kuiper Belt (50500AU) or Oort Cloud (to 50,000AU),
– Tails only when near Sun (vaporised ice),
blown out by the solar wind & sunlight.