Weight on Other Planets
The Fundamental Difference: Mass vs. Weight
To understand planetary gravity, you must first unlearn what "weight" means in everyday conversation. In physics, Mass and Weight are distinct concepts that behave very differently in space.
- Mass (Scalar): This is a measure of how much matter (atoms) you are made of. It measures your inertia—how hard it is to push you. Your mass is exactly the same on Earth, on Mars, or floating in the void of deep space. It is measured in Kilograms (kg).
- Weight (Vector): This is a Force. It is the result of a planet's gravity pulling on your mass. Formula: Weight = Mass × Gravity. Because gravity changes depending on where you are in the universe, your weight is variable.
When you use this calculator, your "Mass" remains constant, but the "Gravity" variable changes, resulting in a different "Weight."
How Planetary Gravity is Calculated
Why does Jupiter crush you while the Moon makes you float? Gravity isn't random; it is governed by Newton's Law of Universal Gravitation.
The strength of gravity ($g$) on any planet surface depends on two things:
- The Mass of the Planet ($M$): Heavier planets have stronger gravity.
- The Radius of the Planet ($r$): How far the surface is from the center core. Gravity gets weaker the further away you are (Inverse Square Law).
The Jupiter Example: Jupiter is 318 times more massive than Earth (which should create huge gravity), but it is also 11 times wider (which weakens gravity). The math balances out to a surface gravity of roughly 2.5x Earth. If Jupiter were the same size as Earth but kept its mass, the gravity would be thousands of times stronger, instantly crushing anything on the surface.
The "Gas Giant" Problem: Where is the Surface?
You might notice we include Jupiter, Saturn, Uranus, and Neptune in this calculator. However, these are "Gas Giants." They do not have a solid rock surface to stand on.
If you tried to land on Saturn, you would simply sink through the clouds until the pressure crushed your spaceship. So how do we calculate surface gravity?
Scientists define the "Surface" of a gas giant as the altitude where the atmospheric pressure is equal to 1 Bar (Earth's sea-level pressure). The numbers in our calculator represent what you would weigh if you could somehow "hover" or stand on a platform at that specific altitude in the cloud layer.
Human Biology in Low Gravity
Knowing your weight on Mars (38% of Earth) is fun, but it presents massive challenges for future colonization (like Elon Musk's SpaceX plans).
Our bodies evolved to fight 1G of Earth gravity constantly. If you move to Mars:
- Muscle Atrophy: Your legs no longer need to work hard to hold you up. Without intense exercise, muscles shrink rapidly.
- Bone Density Loss: Bones are like muscles; if you don't stress them with weight, they dissolve. Astronauts can lose 1-2% of bone mass per month in space.
- Fluid Shift: Without gravity pulling blood into your legs, fluid rushes to your head, causing "Puffy Face" syndrome and sinus congestion.
Comparative Gravity Chart
Here is how the celestial bodies in our solar system rank from weakest to strongest.
| Body | Surface Gravity (m/s²) | Strength vs Earth |
|---|---|---|
| Pluto | 0.62 | 6% (Weakest) |
| Moon | 1.62 | 16% |
| Mars / Mercury | 3.7 | 38% |
| Venus | 8.87 | 90% (Almost Earth) |
| Earth | 9.81 | 100% (Standard) |
| Jupiter | 24.79 | 252% (Strongest Planet) |
| The Sun | 274.0 | 2,790% (Crushing) |
What About the Sun?
The Sun is technically a star, not a planet, but it contains 99.8% of the mass in our entire solar system. Its gravity is what holds all the planets in orbit.
If you weigh 150 lbs on Earth, you would weigh over 4,000 lbs on the Sun. Of course, this is purely theoretical—the surface temperature of 5,500°C (10,000°F) would vaporize you and the scale instantly!