It’s commonly thought of as one of the major planets in our solar system, but Mars is not that big of a planet. It is the second smallest planet in the solar system after Mercury (Earth is the 4th smallest). Since Mars is one of the most similar planets to Earth in the solar system, and among the nearest (only Venus is closer) it’s well worth making a comparison of Earth and Mars in terms of size.
How big is Mars?
Mars has a diameter about one half of Earth’s diameter. It’s approximately 53% of the distance across Earth, but that varies depending where you take the measurement. Like Earth, Mars has an irregular shape, and features a bulge around its equator, so its equatorial circumference is 100 miles further than the distance around Mars traveling through both poles. The diameter of Mars at the equator is 4222 miles (6794 kilometers) compared with 4196 miles or 6752 km when measuring pole to pole.
Its smaller size means Mars has only 10% of the mass of Earth. The much smaller mass and diameter mean Mars has just 38% of the Earth’s gravitational pull. That means a person or object on the surface of Mars would weigh less than one third of their Earth weight.
Another effect of the smaller size of Mars is that its surface has a far greater curvature than Earth’s. On Mars, the visible horizon is relatively short at just 3 kilometers. That means that a Martian observer would not be able to stand back far enough to take in all of Olympus Mons, the planet’s highest mountain, or stand on its peak and observe anything more dramatic than a gently rolling hillside by Earth standards.
Peaks and Troughs
Olympus Mons is a mighty shield volcano that covers a vast area, sloping gently down from its peak. It stands almost 14 miles high, three times taller than Mount Everest and in fact taller than any other mountain in the solar system. It’s the second highest mountain in the known universe.
Mars is a planet of geological extremes, for it is also home to the solar system’s longest, deepest valley. Valles Marineris is clearly visible from space as a gash in the red surface of the planet. This canyon is 1800 miles (3000 km) long, and at its deepest point is almost 5 times deeper than the Grand Canyon, with walls going 28000 feet (8000 m) down to the valley floor. That’s close to the height of Mt. Everest.
Martian Years and Seasons
A day on Mars is only 39.5 minutes longer than an Earth day, but a Martian year takes almost twice as long as a year on Earth. Mars orbits the Sun in just over 686 Earth days, as it is on a much wider orbit. On average, Mars is 230 million miles (369 million kilometers) away from the sun, compared to Earth’s 93 million miles (149 million km).
Mars experiences seasons just like Earth, because it orbits on a tilted axis tilts, in much the same way. Martian seasons are, like its years, almost twice as long as on Earth.