The goal is, of course, to survive the landing, and in order to do this we must design an appropriate parachute. Galileo demonstrated that an object falling only under the influence of gravity will experience a constant acceleration, ie. Furthermore, Galileo discovered that this acceleration is independent of the body's mass, but dependent only on the strength of gravity on the planet. So, in the absence of an atmosphere, heavy things don't fall faster than light things, but at moderate to large velocities even a thin atmosphere can have a significant effect on a falling body's motion due to the effects of aerodynamic drag. As everyone knows, the atmosphere becomes increasingly resistant the faster one attempts to push through it.
Terminal velocity is attained when one's weight equals the drag imposed by the atmosphere.
Let us briefly examine the factors which determine drag. This means that a change in density, area, or drag coefficient will effect an equal change in drag, but a change in velocity will have a much greater effect, eg, doubling velocity will quadruple the drag. At 100 mph drag is 16 times as great as at 25 mph. When terminal velocity is attained, acceleration stops and the diver continues to fall at a constant speed. While there, as a side trip, try the cool mode of Mars exploration.