The speed an object needs to escape a planet's gravity is called the escape velocity. It depends on the planet's mass and radius. Here's the formula:

v = √(2GM/r)

Where:

* v is the escape velocity

* G is the gravitational constant (6.674 × 10^-11 m³ kg^-1 s^-2)

* M is the mass of the planet

* r is the radius of the planet

Here's what this means:

* Larger planets (more mass) have higher escape velocities. This is because their gravity is stronger.

* Planets with smaller radii have higher escape velocities. This is because the object is closer to the planet's center of gravity.

For example:

* Earth's escape velocity is about 11.2 km/s (6.96 mi/s). This means that an object needs to be traveling at least this speed to escape Earth's gravitational pull and never return.

Important Note: Escape velocity is the minimum speed required to *completely* escape a planet's gravity. If an object is launched at less than escape velocity, it will either fall back to the planet or enter orbit.