How come only earth has gravity?

Answer 1

Earth is not the only object with gravity by any means. All objects with mass exert gravity, depending on their size. Other planets, moons and stars have gravity. We only really notice Earth's gravity, though, because, apart from a handful of astronauts, we never stray far enough from Earth to be affected by any other object's gravity.

The key point is that gravity is greatly reduced by distance. In fact, gravity decreases as the square (value times itself) of the distance. The Moon, relatively close astronomically, causes the ocean tides because as the Earth turns, its gravity exerts a slight pull on the water on Earth that is closest to it. We don't feel any pull at all from the Sun, 93 million miles away, but it is strong enough to keep the Earth and the other planets in their orbits. The Sun is kept in the Milky Way galaxy by the combined pull of millions of stars and the massive center of the galaxy.

At some point between the Earth and the Moon (closer to the Moon), the Moon exerts a gravitational force as great as the Earth's on any object, so an object orbiting there would not fall toward either body. These are called the Lagrangian points or L points. There are Earth observation satellites placed near these points, which are farther away than the geostationary orbits closer to Earth.