Gravity: Why You'd Weigh 380 Pounds on Jupiter (But Only 57 on Mars)

Elle
Nov 21
8 min read

If you've ever wondered what it would feel like to stand on another planet, gravity is where things get interesting. On Mercury or Mars, you could jump three times higher than on Earth. On Jupiter, you'd barely be able to stand up. And on the Moon, well, we've all seen the footage of astronauts bouncing around like they're on trampolines.

But here's the thing that might surprise you: gravity isn't just about size. Jupiter is massive, sure, but Saturn is almost as big, and you'd barely feel heavier there than on Earth. Mercury is tiny but has the same gravity as Mars, which is almost twice its size. The rules aren't quite what you'd expect.

Let's break down how gravity actually works, why it's so different on each planet, and what it would feel like to experience it yourself.

What Is Gravity, Really?

Gravity is one of the four fundamental forces in the universe. Every object with mass attracts every other object with mass. Right now, you're pulling on the Earth, and the Earth is pulling on you. You're also pulling on your phone, your chair, and technically every star in the galaxy. But because you're relatively tiny compared to a planet, your gravitational pull is so weak it's basically undetectable.

The strength of gravitational attraction between two objects depends on two things: their masses and the distance between them. Isaac Newton figured this out and gave us the formula: F = G(m₁m₂/r²), where F is the force, m₁ and m₂ are the masses, r is the distance between their centers, and G is the gravitational constant.

For planets, we usually talk about surface gravity, which is the gravitational pull you'd feel standing on the surface (or, for gas giants, floating at the top of their clouds). On Earth, surface gravity is 9.8 m/s², which means if you drop something, it accelerates toward the ground at 9.8 meters per second every second. We call this 1 g, and it's the standard we use to measure gravity everywhere else.

The Surprising Role of Density

Here's where it gets interesting. You might think bigger planets automatically have stronger gravity, but that's not the whole story. Density matters just as much as size.

Think about it this way: gravity pulls you toward the center of mass of an object. If a planet is huge but made of fluffy, low-density gas, most of its mass might be spread out really far from the center. You'd be standing (or floating) on the outer edge, far from where most of the mass actually is, so the pull would be weaker than you'd expect.

Mercury is the perfect example. It's the smallest planet in the solar system, but it's incredibly dense (5.427 g/cm³, almost as dense as Earth's 5.514 g/cm³). All that mass is packed tightly together. Mars, on the other hand, is almost twice the size of Mercury but much less dense. The result? They have the exact same surface gravity: 0.38 g, or about 38% of Earth's gravity.

Similarly, Uranus is huge (four times Earth's radius and over 14 times more massive), but its low density means the surface is far from the planet's core where most of the mass sits. The result is that Uranus actually has weaker gravity than Earth, only about 0.89 g.

This is why you can't just look at a planet's size and know what the gravity will be like. You need to know both its mass and its radius.

A Tour of Planetary Gravity

Let's go through the solar system and see what you'd actually experience on each planet. Imagine you weigh 150 pounds on Earth.

Here's what would happen:

Mercury: 0.38 g (3.7 m/s²)

You'd weigh just 57 pounds on Mercury. Despite being the smallest planet, Mercury is surprisingly dense thanks to its huge iron core. You could jump about 2.6 times higher than on Earth, though the lack of atmosphere and extreme temperatures (ranging from 800°F in sunlight to -290°F in shadow) would be bigger problems than the low gravity.

Venus: 0.90 g (8.9 m/s²)

At 135 pounds, you'd barely notice the difference from Earth. Venus is often called Earth's twin for good reason, with similar size, mass, and density. The gravity feels almost identical. Of course, the 900°F surface temperature and crushing atmospheric pressure equivalent to being 3,000 feet underwater would make it rather unpleasant.

Earth: 1.0 g (9.8 m/s²)

This is our baseline at 150 pounds. We evolved here, so 1 g is what feels "normal" to us. Everything about human biology, from our bone density to our cardiovascular system, is optimized for this gravity level.

The Moon: 0.17 g (1.6 m/s²)

You'd weigh just 25 pounds on the Moon, and this is one place where humans have actually experienced it. The Apollo astronauts found they could jump about six times higher than on Earth and needed the famous "bunny hop" to move around efficiently in their spacesuits. The lunar landing modules had to be carefully designed because objects falling in 1/6th gravity accelerate much more slowly.

Mars: 0.38 g (3.7 m/s²)

At 57 pounds, Mars would feel similar to Mercury. You'd probably adapt pretty quickly, since it's not so low that you'd float around helplessly but low enough that physical tasks would be noticeably easier. The big unknown is whether humans can stay healthy long-term in 0.38 g. We know that extended periods in microgravity (like on the International Space Station) cause bone loss and muscle atrophy. Would Mars gravity be enough to prevent this? We don't know yet.

Jupiter: 2.53 g (24.8 m/s²)

Here's where things get heavy. You'd weigh 380 pounds on Jupiter. Walking would be exhausting, your joints would ache, and standing for extended periods would be difficult. But here's the catch: Jupiter doesn't have a solid surface. It's a gas giant, so we're measuring gravity at the top of its cloud layers. If you could somehow stand there, you'd be dealing with crushing atmospheric pressure, freezing temperatures, and violent winds, not to mention that you'd slowly sink through the clouds toward the (theoretical) rocky core deep below.

What's fascinating about Jupiter is that despite being 318 times more massive than Earth, its gravity is only 2.5 times stronger. That's because Jupiter is so large that its "surface" (the cloud tops) is really far from its center of mass.

Saturn: 1.07 g (10.4 m/s²)

You'd weigh 160 pounds, barely more than on Earth. This is the surprise planet. Saturn is almost as large as Jupiter and 95 times more massive than Earth, but its incredibly low density (0.687 g/cm³, less dense than water) means the cloud tops where we measure gravity are very far from where most of the mass is concentrated. Saturn is so light and fluffy for its size that it would theoretically float in water, if you could find a bathtub big enough.

Uranus: 0.89 g (8.7 m/s²)

At 133 pounds, you'd actually weigh less on Uranus than on Earth, even though Uranus is 4 times bigger and 14.5 times more massive. Again, low density is the culprit. The planet's mass is spread out over such a large volume that the surface gravity is weaker than you'd expect.

Neptune: 1.12 g (11.0 m/s²)

You'd weigh 168 pounds, just slightly more than on Earth. Neptune is slightly smaller than Uranus but more dense, which is why its gravity is a bit stronger. Still, for a planet 17 times more massive than Earth, the surface gravity is surprisingly close to home.

Why This Matters for Space Exploration

Understanding planetary gravity isn't just a fun thought experiment. It's critical for human space exploration and potential colonization.

Landing and launching spacecraft requires precise calculations of local gravity. The amount of fuel needed to land on a planet or moon and then take off again depends entirely on the strength of gravity. This is why it was relatively "easy" for the Apollo missions to land on the Moon and return, but landing on and returning from Mars is vastly more complicated.

Human health is deeply affected by gravity. We know from decades of astronaut experience on the International Space Station that prolonged exposure to microgravity causes bone density loss (about 1-2% per month), muscle atrophy, cardiovascular changes, and vision problems. The big question is: how much gravity is enough? Would living on Mars at 0.38 g be sufficient to keep humans healthy, or would we face the same degradation issues? What about raising children in low gravity? Would their bones and muscles develop normally? These are questions we need to answer before establishing permanent settlements on other worlds.

Gravity assists are a clever technique where spacecraft use a planet's gravity to change speed and direction without using fuel. By flying close to a planet, a spacecraft can steal a tiny bit of the planet's orbital momentum and get a speed boost. The Voyager 2 probe used gravity assists from Jupiter, Saturn, Uranus, and Neptune to make its grand tour of the outer solar system. Without these gravitational slingshots, the mission would have been impossible.

What Would It Actually Feel Like?

Scientists have tried to simulate different gravity levels on Earth, though it's tricky. You can't really create lower gravity without going to space, but you can simulate higher gravity using centrifuges. Pilots and astronauts train in these to experience what 2 g, 3 g, or higher feels like.

At 2 g (like a lighter version of Jupiter), your body feels twice as heavy. Your arms tire quickly, your face sags, and standing up from a seated position takes real effort. Fighter pilots experience 6-9 g during tight maneuvers and need special suits to prevent blood from pooling in their legs and causing them to pass out.

For lower gravity, the closest we've come is parabolic flight, where an airplane flies in a specific arc that creates brief periods of weightlessness or reduced gravity. The Apollo astronauts trained this way to get a feel for lunar gravity.

One interesting experiment involved dropping a ball from 1,000 meters on different planets (in a simulation) to visualize gravity differences. On Jupiter, the ball hits the ground in just 2.69 seconds. On Earth, it takes 14.3 seconds. On the Moon, it would take a full 53.3 seconds. On tiny Pluto (0.07 g), it would take an astonishing 159 seconds, or almost 3 minutes.

The Bottom Line

Gravity across the solar system ranges from the barely-there 0.07 g on Pluto to the bone-crushing 2.53 g on Jupiter. But it's not a simple matter of bigger planets having stronger gravity. Density, distance from the core, and the composition of the planet all play crucial roles.

For humans, this matters enormously. We evolved in 1 g, and moving to environments with drastically different gravity will have profound effects on our bodies. If we're serious about becoming a multi-planet species, we need to understand not just whether we can survive in different gravities, but whether we can thrive.

Can humans have healthy children on Mars? Will astronauts traveling to Jupiter need special suits to cope with 2.5 g? Would living on the Moon's 0.17 g cause irreversible health problems? These aren't science fiction questions anymore. They're practical engineering and medical challenges we'll need to solve in the coming decades.

And the next time you jump, take a moment to appreciate Earth's gravity. It's kept us grounded for billions of years, and it's perfectly tuned for the bodies we have. Anywhere else in the solar system, you'd feel like a stranger in your own skin.