Terrestrial Planets: Mercury and the Moon

Terrestrial Planets

Small, rocky planets with relatively thin or no atmospheres, few moons, and made from heavy elements, located in the inner solar system.

Frostline

A boundary in the protoplanetary disk, inside of which only metals and rocks can form planetesimals, while outside of which hydrogen compounds can also solidify.

Planetesimals

Small celestial objects formed from the sticking together of tiny particles in a protoplanetary disk, serving as the building blocks of planets.

Heavy Bombardment

A period characterized by a high frequency of impacts from planetesimals on planetary surfaces, which ended approximately 4 billion years ago.

Craters

Depressions on a planetary surface formed by the impact of planetesimals, typically varying in size and often overlapping.

P Waves

Primary seismic waves that compress and expand material in the direction they travel, capable of moving through both solids and liquids.

S Waves

Secondary seismic waves that move material side to side and can only travel through solids; they do not travel through liquids.

Convection

The process by which hot rock rises and cooler rock sinks within a planet's mantle, facilitating the transfer of heat from the interior to the surface.

Radiation

The process by which infrared light carries energy away from the surface of a planet, affecting its cooling rate.

Differentiation

The process by which heavier materials, such as iron and nickel, sink to a planet's core while lighter materials float to the surface.