A lander is a spacecraft which descends toward and comes to rest on the surface of an astronomical body. For bodies with atmospheres, the landing occurs after atmospheric entry (or less precisely for other planets, atmospheric reentry) and the lander is first a re-entry vehicle. In these cases landers may employ parachutes to slow down and to maintain a low terminal velocity. Sometimes small landing rockets are fired just before impact to reduce the impact velocity. The Mars Pathfinder mission also used inflatable airbags to cushion the lander's impact. When a high velocity impact is planned, the spacecraft is called an impactor.
Several terrestrial bodies have been subject of lander and/or impact exploration: among them the planets Mars and Venus and the Saturn moon Titan. Of the inner Solar System planets, Mercury is the only one yet to be visited by a lander.