Surface Simulation

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As of Update 24, Universe Sandbox simulates several surface properties of Planetary Body objects in two dimensions, to represent the variation in these properties across the surface of each object. The Surface view at the top of an object's View Panel can display a map representing any of these properties.

Related Properties & Settings[edit | edit source]

Properties[edit | edit source]

The following properties can be simulated:

  • Temperature represents the surface temperature at each point on the map. Temperature is displayed using the same units as Surface Temperature.
  • Elevation represents the height of each point on the map. Elevation is displayed using the same units as Radius.
  • Displacement represents the change in the height of each point of the map relative to the original elevation. Displacement is displayed using the same units as Radius.
  • Vapor Mass represents the amount of vapor (water or CO2 in its gas state) in each point on the map. Vapor Mass is displayed using the same units as Mass.
  • Water/Liquid CO2 Depth represents the height of the surface of the water (or liquid CO2) above the sea floor in each point on the map. Water/Liquid CO2 Depth is displayed using the same units as Radius.
  • Ice Thickness represents the thickness of the ice (solid water or CO2) layer in each point on the map. Ice Thickness is displayed using the same units as Radius.
  • Lapse Rate represents the rate at which temperature changes with altitude. This property depends on the surface pressure of the object and determines where snow appears on the surface. Lapse Rate is displayed in units of °C/m or °C/km.

Settings[edit | edit source]

The surface map for each of these surface properties can be displayed by using the Layer setting in the object's View Panel.

Models[edit | edit source]

Temperature[edit | edit source]

The Temperature layer represents the surface temperature of each point on the map of the object's surface. The temperature calculations consider the effects of incoming heat from sources like nearby stars, the effects of cooling, and the spread of heat across the surface of the object.

Elevation and Displacement[edit | edit source]

The Elevation and Displacement properties represent the height of every point on the surface map and the change in that height, respectively.

The Elevation map of certain known planets in the Solar System, including Mercury, Venus, Earth, and Mars, is stored in the Universe Sandbox database and based on actual data for these planets. The elevation maps of other objects, like exoplanets and randomly generated planets, are randomly generated.

The Displacement map of an object is empty at the beginning of a simulation. If the Elevation of the object's surface is changed, the Displacement map shows how much each grid cell has been changed from its original elevation. A positive value on the Displacement map indicates that the Elevation value of that cell has decreased, and a negative value indicates that the Elevation value of that cell has increased.

The Elevation map of an object can currently be changed via impacts, which will create craters that will decrease the elevation in some areas of the surface, and material is excavated, and increase the elevation in other areas, as debris is deposited on the surface.

Left: The Earth with no water, seen with the default Universe Sandbox view. Right: The Elevation map drawn on the Earth's surface.

Lapse Rate and Snow[edit | edit source]

Universe Sandbox includes a graphical representation of snow that will be present on mountain peaks above a certain elevation if water is present. The snow is not directly simulated, like ice and water are.

The resolution of the simulated surface of an object in Universe Sandbox is generally lower than the resolution of the heightmap used to display the object in a simulation. This is due to the performance demands of surface simulation. If Universe Sandbox used only the Temperature map to calculate where snow should be displayed on the surface, the distribution of snow would have a lower resolution than the rest of the graphical surface.

Instead, within each grid cell, Universe Sandbox calculates how temperature changes with the elevation of the high-resolution heightmap, and uses this temperature to determine where snow is present. The relationship between temperature and elevation depends on the Lapse Rate of temperature, or the rate at which temperature changes with altitude. The Lapse Rate depends on the Surface Pressure, Surface Gravity, and Temperature, and will vary across the surface.

Lapse Rate measures the change in temperature based on the change in elevation from sea level, and is displayed in the following units:

  • Degrees Celsius per meter (°C/m)
  • Degrees Celsius per kilometer (°C/km) = 0.001 °C/m

Material Phases[edit | edit source]

Universe Sandbox tracks three phases of a surface material (either water or CO2) across the surface of the object. At every time step, at every point on the surface map, Universe Sandbox calculates how much of this material will exist as a solid, liquid, or gas. The temperatures at which the material changes between these phases (e.g., the Boiling Point or Freezing Point) depend on several properties of the object, including its Surface Pressure.

The amount of material that exists as a solid at a given point on the surface is represented by the Ice Thickness, the amount of liquid by the Water/Liquid CO2 Depth, and the amount of gas by the Vapor Mass. Liquid and gas material can also move across the surface (see below).

Vapor Flow[edit | edit source]

The movement of gaseous material (either water vapor or CO2) across the surface of the object is simulated with a method similar to the one used to simulate heat diffusion. Vapor flows from areas of high density to areas of low density, so the vapor in a single point on the surface map of an object may spread or diffuse into nearby points, and the vapor in those points may spread to the first point. Universe Sandbox calculates this diffusion by using the FTCS method.

In addition, the speed and direction with which vapor flows across the map is affected by a simulated Coriolis force and the size of the object, as well as the Elevation difference between regions of the surface.

The amount of vapor of each point on the surface map is then updated based on the results of this diffusion calculation.

Liquid Flow[edit | edit source]

The movement of liquid material (either water or liquid CO2) across the surface of the object is simulated with a method similar to the one used to simulate heat diffusion and vapor flow. The rate at which liquid flows in each direction is determined by the difference in elevation in nearby regions, as well as the Surface Gravity of the object.

Limitations[edit | edit source]

Surface Map Resolution[edit | edit source]

Time Step Limitations[edit | edit source]