The Tallest Mountain in the Solar System Is Much Higher Than Everest

Most people are surprised to learn that the tallest mountain in the solar system is not on Earth. After all, there aren't that many other terrestrial – also called "rocky" – planets and moons in the solar system big enough to have a huge mountain.

But in fact, the tallest mountain in the solar system is Olympus Mons on Mars. It's hard to conceive, but this giant stratovolcano rises 16 miles or 84,480 feet (25 kilometers) above the surface of the red planet – and is one of a dozen huge volcanoes on Mars. For comparison, the tallest volcano on Earth, Mauna Kea, is just 6 miles (10 kilometers) high, and only 2.6 miles (4.1 kilometers) can be seen above sea level.

Even more impressive, at the peak of Olympus Mons, a huge caldera (crater) stretches some 50 miles (80 kilometers) across it. Meanwhile, the base of Olympus Mons is 341 miles (549 kilometers) wide – basically the length of the state of Mississippi.

Olympus Mons is more than twice as tall as Mount Everest, which might seem odd given that Mars is half Earth's size by diameter. Scientists hypothesize that Olympus Mons and its monstrous siblings grew so tall due to three different factors.

First, Mars is a much more volcanically active planet than Earth. While our planet certainly had a period of intense volcanic activity long ago, Mars has been much more volcanically active for longer.

Additionally, the tectonic plates on Mars move more slowly than they do here on Earth. This allows huge mountains to form – and remain – while giant mountains on Earth might be pushed under other tectonic plates – what planetologists call the process of subduction – or otherwise affected by tectonic activity.

Finally, the pull of gravity on Mars is only about 38 percent as strong as it is on Earth, due to differences in the mass of each planet. Planetologists believe this may allow mountains to "grow" taller, since gravity doesn't pull down the magma the same way as it does on Earth.

These forces together have allowed Olympus Mons to form as the biggest mountain in the solar system and remain that way over the billions of years in our solar system's history.

If the tallest mountain in the solar system is on Mars, how do the tallest planets of our planet stack up?

While most people know that Mount Everest is the tallest mountain on Earth, its 29,029-foot (8,848-meter) elevation only makes it the tallest mountain above mean sea level. That actually does not make it the tallest mountain on the planet. Mauna Kea in Hawaii is generally considered to be the tallest mountain on Earth, rising 33,500 feet (10,210 meters) above the seafloor.

And if you want to get really technical, the tallest mountain from the center of Earth is Mount Chimborazo. This stratovolcano in Ecuador rises over 6,800 feet (2,072 meters) taller than Everest (2,329 feet or 710 meters taller than Mauna Kea). This is due to the Earth’s centrifugal bulge – the fact that the Earth is actually slightly wider near the equator.