Stand on a bathroom scale and it reads 160 pounds. That number seems like a fixed property of your body, but it isn't — it's the result of Earth's gravity pulling on your mass. Take that same body to Mars and the scale reads 61 pounds. On Jupiter it reads 405 pounds. On the surface of the Sun, if you could survive for an instant, it would read roughly 4,464 pounds. Your body hasn't changed at all. Only gravity has.
Weight vs Mass: The Key Difference
Mass is the amount of matter in your body, measured in kilograms. It is constant throughout the universe. A 70 kg person has 70 kg of mass on Earth, on Mars, in deep space, and on the surface of Pluto.
Weight is the force that gravity exerts on that mass. It is calculated as:
Weight (N) = Mass (kg) × Gravitational acceleration (m/s²)
On Earth, gravitational acceleration at the surface is approximately 9.8 m/s² (often written as 1g). A 70 kg person weighs:
Weight = 70 kg × 9.8 m/s² = 686 Newtons = 70 kg-force
When we say someone "weighs 70 kg," we're informally using mass units for weight — which works fine on Earth, where g is constant. The moment you travel elsewhere, the distinction becomes essential.
Surface Gravity of Every Planet
Surface gravity depends on a planet's mass and radius. Larger mass increases gravity; larger radius decreases it (you're farther from the center of mass). This is why Saturn, despite being nearly 100 times more massive than Earth, has a surface gravity only slightly above Earth's — its enormous radius more than compensates.
| Body | Surface Gravity (relative to Earth) | m/s² | Your Weight if 70 kg on Earth |
|---|---|---|---|
| Sun | 27.9g | 273.7 | 1,953 kg (19,159 N) |
| Mercury | 0.38g | 3.72 | 26.6 kg |
| Venus | 0.91g | 8.87 | 63.7 kg |
| Earth | 1.00g | 9.80 | 70.0 kg |
| Moon | 0.166g | 1.62 | 11.6 kg |
| Mars | 0.38g | 3.72 | 26.6 kg |
| Jupiter | 2.53g | 24.8 | 177.1 kg |
| Saturn | 1.07g | 10.4 | 74.9 kg |
| Uranus | 0.89g | 8.69 | 62.3 kg |
| Neptune | 1.14g | 11.15 | 79.8 kg |
| Pluto | 0.063g | 0.62 | 4.4 kg |
Note: Jupiter, Saturn, Uranus, and Neptune are gas giants with no solid surface. The "surface gravity" values above represent the gravity at the cloud tops, defined at 1 bar of atmospheric pressure. You could not stand on these planets.
The Formula: Weight on Another Planet
The conversion is straightforward:
Weight_planet = Weight_Earth × (g_planet / g_Earth)
Or equivalently, using the gravitational ratio directly:
Weight_planet (kg) = Mass (kg) × g_planet_ratio
Worked example — 70 kg person on Mars:
Mars gravity = 0.38g
Weight on Mars = 70 kg × 0.38 = 26.6 kg
In Newtons: 70 kg × 3.72 m/s² = 260.4 N
Worked example — 85 kg person on Neptune:
Neptune gravity = 1.14g
Weight on Neptune = 85 kg × 1.14 = 96.9 kg
In Newtons: 85 kg × 11.15 m/s² = 947.75 N
Fun Examples: Jumping Height on Each Planet
How high you can jump depends inversely on surface gravity. If you can jump 0.5 meters (about 20 inches) on Earth, the same muscular effort takes you to:
Jump height on planet = Jump height on Earth × (g_Earth / g_planet)
Jump height comparison (baseline: 0.5m jump on Earth):
| Body | Jump Height | Notes |
|---|---|---|
| Moon | 3.0 m (9.8 ft) | Nearly 3 times your height |
| Mars | 1.32 m (4.3 ft) | Like jumping onto a high table |
| Mercury | 1.32 m (4.3 ft) | Same as Mars — identical gravity |
| Venus | 0.55 m (1.8 ft) | Nearly Earth-like |
| Jupiter | 0.20 m (7.9 in) | Barely off the ground |
| Pluto | 7.9 m (26 ft) | Higher than a 2-story building |
On the Moon, a 0.5m vertical jump on Earth translates to a 3-meter leap. Apollo astronauts documented this experience — despite wearing bulky spacesuits adding 80+ kg of mass, they could easily jump 1–2 feet off the lunar surface and take several seconds to land. Running in a spacesuit became a bounding, slow-motion experience.
Why You'd Be Crushed on Jupiter
Jupiter's surface gravity of 2.53g sounds survivable — after all, athletes routinely experience 2–3g during intense activity. But several compounding factors make Jupiter lethally hostile:
No solid surface. Jupiter is a gas giant. Descending into its atmosphere, pressure increases exponentially. At depths reachable by a probe, pressures reach millions of atmospheres. Any physical structure would be crushed before reaching any surface.
Crushing atmospheric pressure. Jupiter's atmosphere at cloud-top level already has 1 bar of pressure — similar to Earth's sea level. Just 100 km deeper, pressure reaches 1,000 bars. Materials strong enough to survive such pressures don't exist in engineered structures.
The 2.53g effect on the human body. Sustained exposure to 2.5g causes cardiovascular strain as the heart must work much harder to pump blood upward to the brain. Extended periods at 2g+ lead to orthostatic hypotension, cardiovascular enlargement, and eventually heart failure. Even if all other factors were controlled, sustained 2.53g is incompatible with long-term human habitation.
Radiation. Jupiter's magnetic field traps intense radiation belts far more energetic than Earth's Van Allen belts. A human inside Jupiter's radiation environment would receive a lethal dose within hours.
The Moon and Mars: Future Human Habitats
The Moon and Mars are the only bodies in our solar system where near-term human colonization is scientifically plausible. Both have far lower gravity than Earth, which creates significant physiological challenges:
Muscle atrophy: On the Moon (0.166g) and Mars (0.38g), the muscular effort required for normal movement is substantially reduced. Without countermeasures, muscles and bones weaken from reduced load-bearing. ISS astronauts spending 6 months at 0g lose 1–2% of bone density per month without intensive exercise regimens.
Bone density loss: Weight-bearing bones (spine, hips, femur) respond to gravitational load by maintaining density. At 0.38g, the stimulus is reduced but still present — Mars is expected to be better for bone health than microgravity but worse than Earth. Estimates suggest Mars-gravity bone loss might require supplementary exercise at perhaps 60% of the intensity required on the ISS.
Developmental effects: The effects of partial gravity on fetal and childhood development are entirely unknown. Animal studies in microgravity show developmental abnormalities, but no long-term partial-gravity studies exist. The 0.38g environment of Mars may or may not support normal human development — this represents one of the most critical unknowns for any multi-generational colony.
Fluid shifts: The human cardiovascular system redistributes fluids under gravity. In low-gravity environments, fluids shift toward the upper body and head, causing facial puffiness, nasal congestion, vision changes (due to increased intracranial pressure), and changes in kidney function. These effects have been extensively documented on the ISS and would be present but less severe at Martian gravity levels.
The contrast between 0.38g on Mars and 1.0g on Earth means that humans who spend years or decades on Mars may become physiologically adapted to Martian gravity and find Earth's gravity — their ancestral home — physically intolerable on return.