The size difference between Earth and Mars is one of the most immediate distinctions between our home world and its closest planetary neighbor. Although both are rocky, terrestrial planets, the disparity in their physical dimensions profoundly affects their geology, atmosphere, and surface conditions. To understand the comparison, we use Earth as the reference point, examining quantifiable metrics like linear distance, total area, and internal substance.
Comparing Diameter and Surface Area
Mars is significantly smaller than Earth in terms of linear measurement. Earth’s equatorial diameter is approximately 12,756 kilometers (7,926 miles), while Mars’s is about 6,779 kilometers (4,212 miles). This means the diameter of Mars is roughly 53% of Earth’s, making the Red Planet slightly more than half the size of our world.
The difference in diameter translates into a larger reduction in total surface area. Earth’s total surface area measures about 510 million square kilometers, while Mars’s surface area is approximately 144.8 million square kilometers. This makes the total surface of Mars only about 28% of Earth’s total surface area.
A relatable comparison arises when considering the land area alone. Since oceans cover about 71% of Earth’s surface, the planet’s total dry land area is about 148.9 million square kilometers. Mars’s entire surface area of 144.8 million square kilometers is almost identical to the total land area found on Earth.
Mass, Density, and Gravitational Force
A planet’s size also involves the amount of material it contains, defined by its mass and density. Mars is less substantial than Earth, possessing only about 11% of Earth’s total mass. Earth’s mass is approximately \(5.97 \times 10^{24}\) kilograms, compared to Mars’s \(6.42 \times 10^{23}\) kilograms.
The difference in mass is compounded by a disparity in density. Earth is the densest planet in the solar system, with an average density of 5.513 grams per cubic centimeter. Mars is substantially less dense, suggesting a smaller, less metal-rich core or a different internal structure compared to our planet.
This combination of lower mass and reduced density results in a weaker gravitational pull on the Martian surface. An object on Mars would experience a surface gravity that is only about 38% of the gravity felt on Earth. A person weighing 150 pounds on Earth would weigh approximately 57 pounds on Mars.
Understanding the Scale of Volume
To appreciate the scale of the size difference, volume provides a final, three-dimensional context. Volume measures the total space a planet occupies, and because it is a cubic measurement, the half-diameter difference results in an enormous volume gap. Mars’s total volume is only about 15% of Earth’s volume.
Approximately six to seven planets the size of Mars could fit inside the volume of Earth. This comparison highlights the difference in the total bulk and interior structure between the two worlds. The contrast in volume, mass, and surface area demonstrates that Mars is physically a much smaller world than Earth.