The human fascination with scale drives us to seek out the extremes of the universe, including the highest peaks. While mountains on Earth are breathtaking, they are dwarfed by the colossal topography found on other planetary bodies. Exploring the solar system reveals geological structures that stretch the imagination. This quest for the largest structure leads directly to a single, extraordinary landmark.
The Tallest Mountain: Name and Dimensions
The title of the tallest mountain in the solar system belongs to Olympus Mons, an immense shield volcano located on the planet Mars. This Martian behemoth rises approximately 22 kilometers, or nearly 72,000 feet, above the surrounding plains. The height is measured from its base, which is defined by a massive escarpment, or cliff face, that is up to 8 kilometers tall in some places.
The sheer breadth of the structure is perhaps even more staggering than its height. Olympus Mons spans a diameter of roughly 600 kilometers, covering an area comparable to the entire state of Arizona or the country of Italy. At its summit, a complex structure of six nested calderas, or collapsed craters, forms a depression that is 85 kilometers wide. The volcano is positioned on the western edge of a vast, elevated volcanic plateau known as the Tharsis Rise.
Scale Compared to Earth’s Peaks
To put the mountain’s size into perspective, a comparison with Earth’s most famous peaks is necessary. Mount Everest, the highest point above sea level on Earth, reaches an elevation of about 8.8 kilometers. Olympus Mons is therefore nearly two and a half times taller than Everest, measured from base to peak, and its volume is almost one hundred times greater than that of Mauna Loa, the largest volcano on Earth.
Even when measuring Earth’s tallest mountain from its true base, the comparison remains lopsided. Mauna Kea in Hawaii, when measured from its base on the ocean floor to its summit, is over 10 kilometers tall. While this measurement is a common point of comparison, Olympus Mons still stands more than twice as tall.
The massive footprint of Olympus Mons means that if you stood on its flank, the slope would be so gentle you could barely perceive it as a mountain. The peak would be so far beyond the horizon that it would be entirely invisible. The mountain’s slopes average a remarkably gradual incline of only about 5 degrees, characteristic of a shield volcano created by highly fluid lava.
How It Grew So Large
The incredible size of Olympus Mons is a direct consequence of the unique geological conditions on Mars. Unlike Earth, Mars lacks mobile tectonic plates, which is the greatest factor in the volcano’s formation. On Earth, plate motion causes the crust to drift over a stationary volcanic hotspot, eventually cutting off the magma supply and resulting in a chain of smaller, progressively older volcanic islands.
On the Martian crust, the absence of plate tectonics means the hotspot remains fixed relative to the surface above it. The constant flow of magma erupted repeatedly in the exact same location for billions of years. This process allowed layers upon layers of basaltic lava to accumulate and build a single, colossal volcanic edifice.
Mars’s lower surface gravity also played a significant role in allowing the structure to reach such heights. With less gravitational pull, the volcanic materials could be stacked much higher before the sheer weight of the structure caused it to collapse. The planet’s thin atmosphere and lack of significant erosion helped preserve the volcano’s structure once it was formed.
Other Massive Features in Space
While Olympus Mons holds the record for the tallest mountain on a planet, the solar system is home to other massive topographical features. Also located on Mars is Valles Marineris, an enormous canyon system that runs for over 4,000 kilometers, nearly a quarter of the planet’s circumference. This massive rift is up to 200 kilometers wide and 7 kilometers deep, making it the largest canyon system known.
Another contender for the title of overall tallest mountain exists on the asteroid Vesta. The central peak of the Rheasilvia impact basin is estimated to rise between 19 and 22 kilometers from its base. This immense feature is a rebound peak created when the asteroid’s surface compressed and then sprang back after a massive impact. Although this central peak is comparable in height to Olympus Mons, the Martian volcano is generally considered the tallest mountain due to its planetary scale and volcanic origin.