Comparing the physical dimensions of planets is one of the most immediate ways to appreciate the vast scale differences in our solar system. By mathematically comparing the total volume of Earth and Mars, we can accurately determine how many of the smaller world could theoretically be contained within the larger. This comparison requires focusing on their three-dimensional space.
The Calculated Number
The direct answer to how many Mars-sized planets can fit inside Earth is approximately 6.4. This number is derived purely from a comparison of the total volume of space each planet occupies. This calculation assumes perfect volume displacement, meaning the Mars-sized objects are theoretically reshaped to perfectly fill Earth’s sphere. The result is a theoretical measure of volume capacity, and it does not consider the planets’ actual mass, density, or geological structure.
Understanding the Size Difference
The significant volume difference is rooted in the planets’ respective radii. Earth’s mean radius is approximately 6,371 kilometers, while Mars’s mean radius is about 3,390 kilometers, making Earth’s diameter roughly 1.88 times greater. Because the two planets are nearly spherical, their volume is calculated using the formula for the volume of a sphere: V = (4/3)πr³.
The volume formula shows that a planet’s size grows dramatically with even a small increase in its radius. The radius value is cubed in the equation, which means it is multiplied by itself three times. This cubing effect is responsible for the massive difference in volume. Since Earth’s radius is nearly double that of Mars, its volume is closer to \(1.88 \times 1.88 \times 1.88\), which mathematically results in the volume ratio of about 6.6 to 1.
The cubed relationship demonstrates why a small increase in diameter leads to such a large increase in total capacity. This mathematical principle ensures that a planet with a radius only slightly less than double another’s will contain over six times the volume.
Visualizing the Planetary Scale
To grasp the magnitude of the 6.4-to-1 volume ratio, it helps to translate the raw numbers into everyday objects. If Earth were scaled down to the size of a basketball, Mars would be comparable to a tennis ball or a large orange held next to it. This visual comparison highlights the dramatic difference in size that the volume calculation reveals.
Another way to visualize the planetary scale is to compare Mars to the Moon. The Moon has a radius of only 1,737 kilometers, meaning Mars is nearly double the size of the Moon. While Mars is a small planet compared to Earth, it is substantial when put next to Earth’s own satellite.