why parachute was used during rover landing on mars but not on moon landing

Parachutes were used during rover landings on Mars, such as the Mars rovers Curiosity and Perseverance, because the Martian atmosphere is dense enough to allow for the deployment of parachutes to slow down the descending spacecraft. On the other hand, parachutes were not used during the Apollo moon landings because the moon has no atmosphere or a very thin atmosphere, making parachute deployment ineffective.

Here's why the use of parachutes differs between Mars and the moon:

1. Atmospheric Density: Mars has a thin atmosphere, but it is still dense enough to provide some aerodynamic drag. This allows spacecraft entering the Martian atmosphere to deploy heat shields to dissipate energy and then deploy parachutes to slow down further. The parachutes provide a controlled descent to a safe landing speed. The moon, on the other hand, has virtually no atmosphere, so there is no air to generate the necessary drag for parachute deployment.

2. Descent Speeds: The absence of atmosphere on the moon means that spacecraft descending to the lunar surface do so primarily under the influence of gravity. Because there is no drag to slow down the descent, the spacecraft's descent stage must rely on rocket propulsion to control and manage its landing speed. The Apollo lunar landers used rocket engines to slow down and maneuver for a controlled landing.

3. Different Design Approaches: The design of spacecraft for Mars and the moon had to consider the specific environmental conditions of each celestial body. Mars missions needed to account for atmospheric entry and aerodynamic forces, which made the use of parachutes effective. Moon missions had to rely on precise rocket-powered descent and landing systems to safely reach the surface.