Mars is the second-smallest planet in the Solar System, and the fourth planet from the Sun. Also referred to as the "Red Planet," Mars has a reddish appearance that is caused by iron oxide on its surface, and can be seen from the Earth with the naked eye. In addition to Earth, Mars may be the only other habitable planet in the Solar System, as well as the only other planet to experience different seasons. Like Earth, Mars also has gravity, but its since its mass is significantly smaller than Earth's, gravity on Mars is weaker than on Earth. The gravity of Mars means that objects with mass around the planet are brought towards it, but its average gravitational acceleration is about 38% that of Earth, or 3.711 m/s², and varies laterally.

**Calculating Gravity on Mars**

In order to determine the gravity of Mars, the gravitational potential (U) and gravitational field strength (G) of Mars need to be measured. The gravity of Mars has been calculated based on the gravitational constant, also referred to as the Newtonian constant of gravitation, which implies that the gravitational force of an object is proportional to its mass. When applied to spherical objects, such as Mars or Earth, with a known mass, the gravity of the surface is inversely proportional to the square of its radius. However, when applied to spherical bodies with given densities, the gravity is approximately proportional to the radius. If the proportionalities are expressed, then g = m/r^{2}, where g represents the surface gravity of Mars, m is the mass, and r is the radius. Both the mass and radius of Mars are expressed as a multiple of Earth’s, which is 5.97610^{24} kg and 6,371 km, respectively. For instance, the mass of Mars is 6.4171 x 10^{23} kg, which is approximately 0.107 times that of Earth, and its mean radius is 3,389.5 km, which is 0.532 times that of Earth. Therefore, the surface gravity of Mars can be calculated as:

g = m/r^{2 }= 0.107/0.532^{2} = 0.107/0.283024 = 0.378

Thus, based on the surface gravity of Earth (9.8 m/s^{2}), the surface gravity of Mars becomes 3.711 m/s^{2}.

**Techniques to Determine Gravity on Mars**

Before spacecraft were able to reach Mars, the only way to estimate its gravitational constant was by deducing properties of the Mars gravity field. The gravitational constant was obtained through Earth-based observation of natural satellites of Mars, such as Deimos and Phobos. The observation of these satellites provided certain parameters, such as eccentricity and semi-major axis, allowing for the calculation of the ratio of the solar mass to the mass of Mars, which give an initial estimate of the gravity field of Mars. However, the arrival of unmanned spacecraft has led to the development of gravity models based on radio tracking data.

**Gravity of Mars and Humans?**

Since the mass of Mars is less than that of Earth, the surface gravity of Earth is higher than that of Mars. The surface gravity of Mars is about 38% that of Earth, meaning that a person weighing 100 pounds on Earth will weigh about 38 pounds on Mars. The long-term effect of human exposure to the amount of gravity on Mars is still unknown. However, ongoing research and simulation suggests that the gravity on Mars would cause certain negative health effects, such as loss of muscle mass, eyesight, and organ functions.