What does it mean?
Comets – are dusty bodies of ice that orbit a star. We typically imagine comets with their characteristic tails; but the tails only form when their orbits bring them close to a star. Comets have three distinct tails: one caused by dust pushed out by radiation pressure from the star, the ion tail caused by stellar winds melting the frozen ice and gas and pushing it back, and a tail of sodium escaping from the dust. The sodium tail is not visible to the naked eye. These tails point in slightly different directions but always away from the star.
In human speak please!
The tour-guide computer talks about how water in a forming solar system is in gas form near the star and in the form of ice further away. What’s another form that water can take? Liquid! That’s right. Scientists call these forms “phases,” and they are either liquid, solid, or gas (there are two others, plasma and Bose-Einstein condensates but we aren’t concerned with those here).
When water is in the ice phase and melts it goes through a “phase transition.” In fact, any time water changes from one phase to another it’s called a “phase transition.”
What other elements or materials can you think of that go through phase transitions?
Is that all?
Solar System Exploration: Comets – Additional information about comets including missions to comets, and threats that comets and asteroids might pose to Earth.