Why your weight changes from planet to planet

Your mass — the amount of matter in your body — is the same everywhere. Your weight is the force of gravity pulling on that mass, and it depends on the world you are standing on. A planet's surface gravity depends on two things: how massive it is, and how far its surface is from its centre.

On the Mars page you can read why a planet with a tenth of Earth's mass still has 38% of Earth's gravity: it is also much smaller, so you stand closer to its centre.
Jupiter is 318 times Earth's mass, but it is so wide that its gravity at the cloud tops is only about 2.5 times ours.
Saturn is 95 times Earth's mass, yet its gravity is almost the same as Earth's.

Why your age changes

A year is the time a planet takes to go once around the Sun. Planets closer to the Sun move faster on shorter paths, so their years are short: a year on Mercury lasts only 88 Earth days. Distant planets have very long years — Neptune takes about 165 Earth years to complete one orbit, so nobody has yet lived a single Neptune year.

Your age on another planet is simply your age in Earth days divided by the length of that planet's year.

How the calculation works

Weight on a planet = your weight on Earth × that planet's surface gravity relative to Earth.
Age on a planet = your age in years × 365.25 ÷ that planet's orbital period in Earth days.

Gravity values and orbital periods come from the NASA Planetary Fact Sheet.

Build your own world

Want a planet with exactly the gravity you like? Read what would happen if Earth were twice as big, or design your own planet.