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What is Olympus Mons?

Michael Anissimov
Updated Jan 31, 2024
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Olympus Mons, meaning Mount Olympus in Latin, is the largest known mountain and volcano in the solar system. Located on Mars, it is 15.5 miles (25 km) tall, more than three times the height of Mount Everest. The mountain is actually a shield volcano, which is a large volcano with shallowly-sloping sides formed through the eruption of lava with low viscosity. Because Mars has no active plate tectonics, this hotspot used to erupt continuously in the same place, slowly building up a bigger and bigger mountain until it became the tallest and widest in the solar system.

Being a shield volcano, Olympus Mons is much wider than it is tall. The mountain is 387.7 miles (624 km) wide, topped by a caldera complex that is 49.7 miles (80 km) by 37.2 miles (60 km) wide, and up to 1.9 miles (3.2 km) deep. At the top, the air density is only 5 to 8% of that at the surface, contrasted with the top of Mount Everest, which experiences about 32% of the air density as found at the Earth's surface.

Because Mars's atmospheric density is only about 1% of the Earth's to start with, the air at the summit is only about 0.05% that of the Earth's — a veritable vacuum. Mars has lower gravity than Earth, so it also has a taller atmosphere, putting the summit of this mountain well within Mars' atmosphere.

If Olympus Mons were on Earth, a person standing on its summit could see 400 miles (643.7 km) to the horizon, in comparison to only about 3 miles (4.8 km) for observers at sea level. On Earth, 15.5 miles (25 km) is about a quarter of the way to the internationally accepted definition of space, 62.1 miles (100 km) above the planet's surface.

This volcano is often compared to Mauna Kea, in Hawaii, because both extremely large shield volcanoes by the standard of their own planet. In fact, Mauna Kea is even taller than Mount Everest, when measured from where it begins on the ocean floor.

It is extremely unlikely any mountains larger than Olympus Mons will be discovered on the rocky planets in the solar system. The discovery of such structures on the rocky cores of gas giants is also somewhat unlikely, because the greater mass of these planets would have a tendency to make them more spherical and thereby less mountainous.

AllTheScience is dedicated to providing accurate and trustworthy information. We carefully select reputable sources and employ a rigorous fact-checking process to maintain the highest standards. To learn more about our commitment to accuracy, read our editorial process.
Michael Anissimov
By Michael Anissimov

Michael is a longtime AllTheScience contributor who specializes in topics relating to paleontology, physics, biology, astronomy, chemistry, and futurism. In addition to being an avid blogger, Michael is particularly passionate about stem cell research, regenerative medicine, and life extension therapies. He has also worked for the Methuselah Foundation, the Singularity Institute for Artificial Intelligence, and the Lifeboat Foundation.

Discussion Comments

By helene55 — On Jul 15, 2011

Wow, 342 miles in width. It is amazing the size of things on other planets compared to our own. I wonder though, if there really were intelligent life on nearby planets, would they think the same about Earth?

By sherlock87 — On Jul 14, 2011

It amazes me that we know so many Olympus Mons facts when it is on Mars, so far away and seemingly unreachable. It would be amazing if people could get there one day, although with space research becoming more and more expensive and the future of things like the shuttle program being uncertain, who knows when someone will see this mountain up close.

By anon7549 — On Jan 29, 2008

when is the last time it erupted at anytime? even a small eruption?

Michael Anissimov

Michael Anissimov

Michael is a longtime AllTheScience contributor who specializes in topics relating to paleontology, physics, biology...

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