Gravity is a fundamental force that exists between objects with mass or energy, including planets. It is the force of attraction that pulls objects towards the center of mass of a planet. Gravity is responsible for keeping planets in orbit around the Sun and for holding everything on the planet's surface.

The strength of gravity depends on two factors: the mass of the planet and the distance from the center of the planet. Generally, the greater the mass of a planet, the stronger its gravitational pull. This is why larger planets tend to have stronger gravity compared to smaller ones. For example, the gas giant Jupiter has a much higher mass than Earth and, therefore, exerts a stronger gravitational force.

Gravity also weakens as you move farther away from the center of the planet. The inverse square law states that the force of gravity decreases with the square of the distance. In other words, the farther you are from a planet, the weaker its gravitational pull becomes. This is why you can jump higher on the Moon, where the gravity is weaker compared to Earth.

The gravity of a planet has various effects. It keeps the planet's atmosphere in place, holds bodies of water on the surface, and determines the weight of objects. The gravity of a planet also affects the orbits of satellites and other celestial bodies around it. For example, the gravitational pull of Earth keeps the Moon in its orbit.