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• 1 media/UpsilonAndromedae_D_moons.jpg 2016-05-09T12:46:05+00:00 Water throughout the Solar System 12 image_header 2019-06-12T17:25:38+00:00 We have already seen that comets are essentially dirty snowballs that evaporate as they get close to the sun.  There are more icy lumps hidden in the Asteroid belt but given our current state of knowledge we expect them to remain frozen lumps.  For the remaining portion of this module, we’ll restrict our examination to the larger and arguably more interesting bodies within the solar system, the planets and their satellites.  We’ll start with our planet as a reference and then move through the solar system.

  Earth, the Blue Planet 

  
  Examining the Earth from space it certainly appears to be a very watery planet as large oceans are clearly visible.  Approximately 71% of the planet is covered in water, giving it its blue appearance.  The average ocean depth is approximately 4 km which means that the total volume of water in the oceans is approximately 1.37 billion km³ (1,370x10⁶ km³).  In addition to the oceans, large ice sheets in Antarctica (21.6 million km³) and Greenland (2.34 million km³) as well as many smaller glaciers lock up water in ice form.  Canada has a tremendous reservoir of freshwater. Canada’s largest 50 lakes each have a surface area of more than 1,000 km².  Groundwater is important as it provides aquifers for many regions. Our thick atmosphere drives an active water cycle that keeps approximately 12,900 km³ of water suspended in it as vapour.  Overall then the water is distributed like this:
  
  
  
  
  
  
  For a great and more in-depth overview of water on this planet, check this page provided by the USGS (United States Geological Survey).
  
  
  Plate tectonics on Earth also has an important influence on the water budget of the planet.  At subduction zones, oceanic floor material returns to the mantle.  This drags a large amount of water back into the mantle.  The interior of the Earth is thought to contain multiple times the amount of water that is found in the oceans and that it plays an important role in mantle convection-related processes.
  
  So, in summary, we have a lot of water on our planet.  Having spent some time here, we expect you are relatively familiar with most modes of occurrence. So, let us now look at other locations within the solar system.  We'll start with a planet you would not normally associate with water.