1.622 and 3.721: Two Gravity Values
Behind these two figures lies one and the same physical notion: the force that keeps our feet on the ground and objects on a table. It follows directly from the mass and radius of each celestial body.
For a space exploration enthusiast, these two numbers sum up the essence of what distinguishes the human experience on the Moon from what a stay on Mars would involve.
- Lunar gravity: 1.622 m/s², or about one sixth of Earth's gravity;
- Martian gravity: 3.721 m/s², or a little more than one third of Earth's gravity;
- Earth's reference gravity: 9.81 m/s².
Why Does the Moon Have a Gravity of 1.622 m/s²? Mass, Radius and Density Explained
The Moon has a mass of about 7.35 × 10²² kg, almost 80 times less than the Earth, for a radius of about 1,737 km (a diameter of 3,474 km), nearly four times smaller than that of our planet.
A smaller radius brings the surface closer to the body's centre, which increases the attraction; but in the Moon's case, its low mass by far outweighs this effect, resulting in a gravity much lower than Earth's.
The Moon's density, close to 3.34 g/cm³ compared with 5.5 for the Earth, points in the same direction: for the same volume, the Moon contains less matter. The result: lunar gravity is about one sixth of what you experience on Earth.
It was this reduced gravity that allowed the Apollo astronauts to bound across the lunar surface with such characteristic lightness, a symbol to which the Col&McArthur Lunar 1,622 pays tribute right down to its name.
Why Does Mars Have a Gravity of 3.721 m/s²? An Intermediate Gravity Between the Moon and the Earth
With a mean radius of about 3,390 km, Mars is almost twice the size of the Moon (1,737 km), yet remains much smaller than the Earth. Its mass, close to 6.42 × 10²³ kg, also falls between the two: about nine times that of the Moon, and one tenth that of the Earth.
Once put into the equation, these two factors result in a gravity about 2.3 times higher than the Moon's, and a little more than one third of Earth's gravity.
Neither the lightness of the Moon nor the familiar weight of Earth: this intermediate position gave its name to the Col&McArthur RED 3,721, designed as a tribute to this frontier between two worlds.
The Link Between These Values and the Lunar 1,622 and RED 3,721 Collections of the Interstellar Universe
At Col&McArthur, since the watchmaking house was founded, every piece has been rooted in an authentic fragment and a precise historical moment. The watches in these two collections of the Interstellar universe are at the very least numbered, and the Swiss automatic versions are limited to 2,020 pieces for the model paying tribute to Mars and 2,025 pieces for the model paying tribute to the Moon.
The Lunar 1,622 draws its inspiration from the conquest of the lunar surface, the Apollo and Artemis missions, and the reduced gravity that allowed the first men to walk there so lightly.
The RED 3,721, for its part, takes its name from Martian gravity, neither quite weightlessness nor quite Earth's weight, a symbol of a frontier that humanity has crossed only through its ingenuity and the Perseverance rover.
For both collections, our approach is the same: to create a watch inspired by History and made with tangible materials that echo these stories, in this case lunar and Martian meteorite dust.
It is this meticulous work that allows Col&McArthur to present prestigious pieces that stand the test of time and, above all, fulfil the house's primary mission: to remember the great achievements of Humanity.
How Is a Body's Gravity Calculated From Its Mass and Radius?
Surface gravity is calculated using the law of universal gravitation:
g = G × M / R²
where G is the gravitational constant (6.674 × 10⁻¹¹ m³·kg⁻¹·s⁻²), M the mass of the body and R its radius. Gravity therefore increases with mass, and decreases with the square of the radius.
For the Moon: (6.674 × 10⁻¹¹ × 7.346 × 10²²) / (1,737,400)² ≈ 1.62 m/s². The same calculation applied to Mars gives about 3.7 m/s².
These figures are therefore not arbitrary: they follow directly from the real characteristics of each body.
What Are the Practical Consequences for the Human Body and Crewed Missions?
On the Moon, an astronaut weighing 80 kg keeps the same mass, but only has the weight that a 13 kg object would have on Earth. Their muscles and bones, far less used, gradually weaken without countermeasures, a phenomenon well documented during long stays in orbit, aboard Skylab and later the International Space Station.
For Mars, the problem arises in two stages: months of travel in weightlessness, followed by a stay on a planet whose gravity, a little more than one third of Earth's, should limit this loss without preventing it.
Every crewed mission must therefore plan for:
- physical training on board, to limit the loss of muscle and bone mass;
- the rehabilitation needed on returning to Earth;
- the adaptation of balance, movement coordination and blood circulation to a different weight;
- the design of habitats and equipment, adapted to a gravity much lower than on Earth.
It is this confrontation between humans and different physical laws that inspired Col&McArthur's approach: to make every timepiece a tangible tribute to the conquest of space.
Frequently Asked Questions
Why is lunar gravity weaker than Martian gravity?
Because the Moon has a much lower mass than Mars, for a radius that is also smaller; the combination of these two factors produces a noticeably weaker surface attraction.
What reference gravity is used to compare these values?
Standard Earth gravity, rounded to 9.81 m/s², serves as the point of comparison for expressing the differences observed on the Moon and Mars.
Are 1.622 and 3.721 values measured at a specific moment?
They are average surface values: gravity varies slightly with latitude and altitude.
Why do these figures carry symbolic meaning at Col&McArthur?
Because the Lunar 1,622 and RED 3,721 of the Interstellar universe are based on real physical data linked to precise historical moments in space exploration, as an act of remembrance rather than mere ornamentation.
