Topic 12 - Formation of Planetary Systems

• how long ago did the sun form?

  4.6 billion years
• Gravity is the force responsible for orbits
• accretion is the accumulation of particles into a massive object (e.g. planets) by...?

  Gravitational attraction
• the centre of gravity is called the ?

  barycentre
• the barycentre of planet-moon systems is...?

  within the body of the planet
• what is orbital resonance?

  occurs when orbital periods have exact integer ratios
• Jupiter's moon lo, europa, and ganymede have orbital periods in the ratio 1:2:4
• a 1:1 resonance is unstable and will force the smaller object from its orbit
• what happens at the lagrangian points?

  the gravity of the two bodies cancel each other out
• internal friction caused by tidal forces generate large amounts of energy known as tidal heating.
• what is the minimum distance for a body to avoid being pulled apart by tidal forces?

  the Roche limit
• what is the Roche limit?

   between 2 and 3 orbital radius of the planet
• what would happen if a moon is too close to a large planet?

  the tidal forces can be strong enough to overcome the moons gravitational forces
• if a planet does exceed the Roche limit and is pulled apart it remnants are likely to orbit the planet as ring, (which could be the cause of planetary ring systems)
• evidence for collisions?


  axial tilt of earth

  retrograde spin of venus

  large impact basins
• venus maintains a thick... atmosphere


  carbon dioxide
• earth is within the habitable zone.
• mars has a thin carbon dioxide atmosphere
• what is the internal structure of smaller gas giants?

  rocky core with  an outer core of molecular hydrogen and water-ammonia.
• what is the internal structure of larger gas giants?

  rocky core with an outer core of liquid metallic hydrogen that creates a strong magnetic field
• what is the frost line?

  the imaginary line, which beyond it there are low temperatures allowing volatile compounds to condense
• what is an exoplanet?

  a planet that orbits a star not in our solar systm
• why is it difficul to observe exoplanets?

  even when using a telescope stars appear as points of light
• what are three methods used to observe exoplanets?

  transit method, radial velocity, astrometry
• describe how the transit method works?


  when an exoplanet transits a star we may detect a dip in the light emitted by the star
• what can the transit method be used to calculate?

  size and orbit of a planet
• looking for any minute wobbles  in a star's position compared to the positions of other stars is known as...?

  astrometry
• what is radial velocity?


  Changes in the movement of a star towards and away from Earth can be detected using the Doppler effect.
• which moons are candidates of life being present?

  Europa, Enceladus, Titan
• what makes titan thought to have had life in the past?

  thick atmosphere with organic compounds including methane
• what makes europa a candidate for life?

  liquid water has been discovered beneath crust, caused by tidal forces
• what makes enceladus a candidate for life?

  icy surface with liquid water underneath, jets of water shoot through the crust into space and organic compounds have been detected
• what is the goldilocks zone?


  zone around the star where liquid water can exist
• the hotter the star the wider the habitable zone is which starts closer to the star
• what does the drake equation calculate?

  the number of advanced civilizations likely to exist in the Milky Way galaxy
• what does SETI stand for?

  search for extra terrestrial life
• benefits of discovering extra terrestrial life?

  Intelligent life may share advances in technology

  Intelligent life may share knowledge about science

  Alien forms of life could lead to cures for existing illnesses
• dangers of discovering extra terrestrial life?

  They could also create new bacteria capable of killing all life

  set out to invade or hurt Earth life forms including humans

  Depending on an unknown alien force for knowledge prevents us from advancing as humans