The local gravitational field strength at the surface of an astronomical body. It determines, for example, how much a person would weigh if they were to stand on that object. In the case of a gas giant or a star, the surface gravity is calculated as if there were a solid surface at the top of the atmosphere.
Local gravitational field strength is given by g, the force acting on a mass of 1 kg at the surface, according to the formula g = GM/r 2, where M is the mass of the body, r its radius, and G the gravitational constant (= 6.67 × 10-11 Nm2). Thus greater mass means greater surface gravity, but greater diameter means lesser surface gravity. For the Earth, g has a value of about 9.8 newtons/kg. For Mars, by contrast, g is only about 3.7 N/kg, or 0.38 times as much. g is also known as the acceleration due to gravity. The table below compares the surface gravity of various bodies to that of the Earth.
The surface gravity of a world is expected to strongly influence what, if any forms of life, may appear on it. For more on this, see alternative forms of life.
Related entry gravity
Related category ASTRONOMICAL QUANTITIES
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