Lecture 2: The Solar System

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Lecture 2The Solar System

• Dr Michael Burton

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Overview

• Formation from collapse of cloud of gas and dust
  4.6 billion years ago.
• Collisions and cratering dominated for first 150
  million years, leaving current planetary system.
• Inventory 1 star, 81 planets, moons, asteroids,
  comets, solar wind.
• Terrestrial (rock) Jovian (gas) planets

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Our Star, the Sun

• Giant ball of plasma undergoing thermonuclear
  fusion of hydrogen in centre!
• Photosphere (visible), chromosphere (spicules
  granules), corona (solar wind) comprise the
  atmosphere.
• Sunspots, magnetic fields and convection, causing
  plages, prominences solar flares.
• Solar Model well understood (neutrinos?).

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Mercury

• Day is two years long (tidal resonance)!
• Cratered surface (impacts), covered by some lava
  flows.
• Iron core and magnetic field.
• Atmosphere (Na) from outgassing of planet.

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Venus

• Dantes Inferno 500C, 100 atmospheres and
  sulphuric acid clouds!
• Runaway greenhouse hidden by cloud.
• Rolling hills, two continents and volcanoes.
• Crust periodically melts?!
• Slowly rotates backwards with no seasons.

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Earth / Moon

• Double planet system, tidally interacting.
• Plate Tectonics produces continents, oceans,
  mountains volcanoes.
• Iron rich core producing magnetic field.
• Supports life on land, oceans atmosphere.
• Moon created via collision-ejection.
• Weathering erased asteroid impacts on Earth but
  past history still visible on Moon.

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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.
• Could life have once existed?
• 2 moons are captured asteroids.

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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.

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Moons of Jupiter

• 16 Moons with 4 giants (Galilean satellites).
• Io Volcanic, molten through tidal heating.
• Europa Ice, tidal heating, life in oceans??
• Ganymede Rock Ice, past tectonics.
• Callisto Rock, cratered terrain (impacts).

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Saturn

• Lord of the Rings.
• Gas giant, much like Jupiter.
• Razor-thin rings of icy rocks (10 cm-10 m).
• Gravitational resonance with moons.
• At least 20 moons.
• Titan with nitrogen hydrocarbon atmosphere,
  ethane oceans - life??

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Uranus

• A bland gas giant.
• Tipped over exaggerated seasons!
• Magnetic axis at 60 to rotation axis.
• 15 Moons, rings.
• Miranda almost shattered by collision.

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Neptune

• A blue gas-giant, similar to Uranus.
• Discovered through prediction from discrepancy in
  motion of Uranus.
• Fastest winds in solar system (1700 km/hr)!
• 8 moons, rings.
• Triton captured - retrograde orbit. Extreme cold
  (36K) but nitrogen geysers! Being pulled into
  Neptune by tides!

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Pluto Charon

• Not really a planet - a double moon system.
• Discovered by chance in 1930.
• Now furthest from Sun (again, just!).
• Rock ice.

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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 primordial balls of ices and rocks
  transient dirty snowballs.
• 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.