Sublimation is the process in which a material changes from a
frozen solid to a gas without passing through the intermediate
liquid state. Whether a material will sublimate (solid to gas),
melt (solid to liquid) or vapourise (liquid to gas) depends on
the temperature and pressure of the environment in which it is
located. This can be illustrated in a 'phase diagram' such as
the one below for water. In this case, and with the pressures (1
atmosphere) and temperatures (25 degrees Celsius) we are
accustomed to on Earth, water ice will melt to form liquid
water, which will then vapourise to form water vapour. However,
if the pressures are low enough (for example, the pressures we
find elsewhere in the Solar System), water ice will turn
directly into water vapour as the temperature increases,
bypassing the liquid water stage. An example of a material that
sublimates here on Earth is frozen carbon dioxide (CO2) - more
commonly known as 'dry ice'. When exposed to room temperature
air at pressures of 1 atmosphere, th