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GENS4001 Astronomy Part 1: The Solar System Dr Michael Burton Department of Astrophysics School of Physics, UNSW Overview 1 Star (the Sun) 8 + 1 Planets Mercury, Venus, Earth, Mars Jupiter, Saturn, Uranus, Neptune Pluto / Charon ≥ 61 Moons

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gens4001 astronomy part 1 the solar system

GENS4001 AstronomyPart 1:The Solar System

Dr Michael Burton

Department of Astrophysics

School of Physics, UNSW

The Solar System

overview
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

The Solar System

formation of the solar system
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
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

The Solar System

the sun continued
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
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.

The Solar System

earth moon continued
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.

The Solar System

earth moon phenomena
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.

What if the Moon didn’t exist?

The Solar System

the inner and outer planets
Small (<13,000 km)

Rocky (iron core)

Thin atmospheres

Slow rotation

Short years

Few moons

Warm

No Rings

Large (>50,000 km)

Gaseous (H, He)

Thick atmospheres

Rapid rotation

Long years

Many moons

Cold

Rings

The Inner and Outer Planets

The Solar System

slide11
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 captured asteroids.
jupiter
Jupiter
  • 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.

The Solar System

moons of jupiter
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).

The Solar System

comets and asteroids
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 (50-500AU) or Oort Cloud (to 50,000AU),
    • Tails only when near Sun (vaporised ice), blown out by the solar wind & sunlight.