How fast must an object go to leave a planets gravity?

The speed that ab object must travel at to escape a planet's gravity is called escape velocity. This value varies depending on the mass and diameter of the planet. Here are the escape volcities of the eight planets of our solar system.

Mercury: 9,400 mph

Venus: 23,000 mph

Earth: 25,000 mph

Mars: 11,000 mph

Jupiter: 133,000 mph

Saturn: 77,000 mph

Uranus: 48,000 mph

Neptune: 53,000 mph

Note that escape velocity only takes gravity into account and ignores other forces. An object launched from Earth's surface or from any other planet with a substantial atmosphere at escape velocity would be quickly destroyed and slowed down by air resistance.