The question of how much a person would weigh on a distant celestial body like Jupiter touches on a fundamental difference in physics: the distinction between mass and weight. Weight is not an inherent property of an object but a measurement of the gravitational force exerted upon its mass. Your physical body, or the matter within it, remains unchanged regardless of where you travel in the universe. Only the force pulling you toward the center of the planet, which we call weight, will vary dramatically. Understanding this concept is the first step toward grasping the physics.
The Specific Weight on Jupiter
If you weigh 150 pounds on Earth, you would weigh approximately 351 pounds on Jupiter. This calculation is based on Jupiter’s surface gravity being roughly 2.34 times that of Earth’s gravity, often expressed as 2.34 g’s. To find the weight, you simply multiply your Earth weight by the planet’s gravitational factor.
This is a theoretical calculation, as Jupiter is a gas giant with no solid surface to stand upon. The gravitational force is measured at the point in Jupiter’s atmosphere where the pressure is equal to the atmospheric pressure at sea level on Earth, known as the 1-bar pressure level. An object sinking below this level would experience increasing pressure and temperature, but the downward gravitational pull would remain intense.
Understanding Mass and Weight
The reason your weight changes while your physical body does not lies in the scientific definitions of mass and weight. Mass is the measure of the amount of matter in an object, which is an intrinsic property that remains constant everywhere in the universe. This quantity also represents an object’s resistance to acceleration, a concept known as inertia.
Weight, conversely, is a measure of the force of gravity acting upon that mass. It is not a fixed quantity but a variable force determined by the celestial body you are near. The relationship is summarized by the formula \(W = m \times g\), where \(W\) is weight (force), \(m\) is mass, and \(g\) is the acceleration due to gravity.
On Earth, the terms mass and weight are often used interchangeably, which can cause confusion when discussing space travel. A common bathroom scale measures the force exerted by your mass against Earth’s gravity, giving you a value in pounds or kilograms. However, if you were to use a balance scale, which compares your mass to a known standard mass, the reading would be the same on Earth, Jupiter, or the Moon.
The distinction means that while a 150-pound person on Jupiter would feel a downward pull of 351 pounds, their mass—the amount of “stuff” making up their body—would be exactly the same as it was on Earth. The increased number simply reflects the greater gravitational acceleration, \(g\), of the giant planet. Weight is measured in units of force, such as Newtons in the scientific community, while mass is measured in kilograms.
The Factors Behind Jupiter’s Gravity
Jupiter’s powerful gravitational field is a direct consequence of its enormous mass, which is 318 times that of Earth’s. According to the law of universal gravitation, the force of attraction between two objects is proportional to the product of their masses. This means that Jupiter’s sheer quantity of matter is the primary driver of its strong pull.
The massive planet is primarily composed of hydrogen and helium, similar to the composition of the Sun. This gaseous nature gives Jupiter a relatively low average density compared to the rocky, terrestrial planets. If Jupiter were as dense as Earth, its surface gravity would be far greater than 2.34 g’s.
The gravitational force experienced at a planet’s surface is also inversely proportional to the square of the distance from the planet’s center of mass. Although Jupiter is extremely massive, its radius is also over 11 times larger than Earth’s. This large distance from the center of the planet to its notional surface significantly mitigates the gravitational acceleration that would otherwise be generated by its colossal mass.
Deep within the planet, the immense pressure compresses the hydrogen into an exotic state called liquid metallic hydrogen. This dense layer, along with a possible core of heavier elements, accounts for the majority of the planet’s mass and is the ultimate source of its powerful gravitational attraction. The balance between its immense mass and its huge radius results in a surface gravity that is strong, but not overwhelming relative to its size.
Weight Comparisons Across the Solar System
Jupiter represents one end of the gravitational spectrum within the Solar System, but other celestial bodies offer a wide range of weights for a 150-pound person.
The Moon
Traveling to the Moon, which has a gravitational pull of only about 0.165 g’s, would make the person weigh just under 25 pounds. This dramatically reduced weight is what allowed Apollo astronauts to bound across the lunar surface.
Mars
On Mars, the gravitational factor is 0.38 g’s, meaning a 150-pound person would weigh 57 pounds. This is a significant decrease, but not as extreme as the Moon. The gravity on Mars is strong enough that humans would still walk with a noticeable downward force, but physical tasks would be much easier than on Earth.
Saturn
Even among the other gas giants, the weight difference is notable. On Saturn, the gravity is slightly less than Earth’s, at 0.93 g’s. This means the 150-pound individual would feel only slightly lighter, weighing about 140 pounds, despite Saturn being a massive planet. This lower surface gravity is due to Saturn’s even lower density compared to Jupiter.