Everyone has had a moment of wishing the bathroom scale said something different. Here's a fun way to make it happen without changing a thing about yourself: take the scale to another world. Depending on where you land, the number could shrink to almost nothing or more than double.
That's because weight isn't the same as mass. Your mass, the amount of stuff you're made of, stays the same everywhere. Your weight is the pull of gravity on that mass, and gravity is different on every planet. A person who weighs 150 pounds on Earth would weigh about 25 pounds on the Moon, about 57 pounds on Mars, and about 379 pounds on Jupiter.
Weight vs. Mass
Scientists measure weight as a force. A one-kilogram object has a weight of about 9.8 newtons on Earth and only about one-sixth as much on the Moon. It's still the same one kilogram of stuff. The Moon just doesn't pull on it as hard.
How strong a planet's gravity feels at its surface depends on two things: how much mass it has and how big it is. More mass means a stronger pull, but being farther from the center weakens it. That's why a huge planet doesn't always have huge gravity.
The Lightweights
The Moon's gravity is about one-sixth of Earth's, so a 150-pound person would weigh about 25 pounds there. That explains the bouncy, slow-motion steps you see in footage of astronauts on the Moon.
Mars and Mercury are close twins on the scale. Mars has about 38 percent of Earth's gravity, and Mercury's is slightly lower. Either way, our 150-pound traveler would weigh roughly 57 pounds.
Little Pluto takes the prize for lightness among these worlds. Its surface gravity is so weak that a 150-pound person would weigh only about 9 or 10 pounds.
The Surprising Middle
Venus is similar in size and mass to Earth, and its gravity is a little weaker. You'd weigh about 136 pounds there. Uranus, despite being a giant, has slightly weaker gravity than Earth, too, putting our traveler at about 133 pounds.
Saturn is the big surprise. It's more than 95 times as massive as Earth, yet its gravity is close to ours, because that mass is spread out over a planet about nine times wider than Earth. In fact, Saturn spins so fast and bulges so much at its equator that gravity there is lower than on Earth. A traveler would weigh somewhere around 150 pounds, give or take.
The Heavyweights
Neptune's gravity is about 1.15 times Earth's, enough to push our 150-pound person up to about 172 pounds. It's surpassed only by Jupiter.
Jupiter is the champion. Its gravity is about two and a half times Earth's, so that same person would weigh about 379 pounds. Just standing up would feel like carrying another person and a half on your back.
There's one catch with the giant planets. Jupiter, Saturn, Uranus, and Neptune don't have solid ground to stand on, so scientists measure their gravity at the level in the atmosphere where the air pressure matches Earth's at sea level. You'd have to float there on an imaginary scale.
So if you ever want a quick confidence boost, just remember that on Pluto, you'd weigh less than 10 pounds. On Jupiter, though, you might want to skip dessert.
