What’s the highest mountain in the solar system?

While I’m in Chile climbing the mountain with the most superlatives in the world, I thought it might be interesting to consider just how superlative a mountain can get.

Most of us have climbed mountains where we’ve not been able to see the summit until we’re standing on it. A few of us have also climbed mountains where the slope has been so gentle that the horizon has remained just a few metres in front of us for much of the ascent (for me, Muztag Ata springs to mind).

But imagine climbing a mountain that’s so big, and the slope so gentle, that you have to keep walking for several days before the summit appears.

Such a mountain exists, but at the moment it’s a job getting there, because the mountain’s on Mars.

This intriguing tweet contains a somewhat perplexing diagram. Not only does the mountain, Olympus Mons, appear to be half as high as the radius of a planet, but the little stick man appears to be nearly as high as the mountain.

To give a better idea of the scale of the giant volcano Olympus Mons, we need a better reference point. It’s over 21km high (compared to Everest’s 8.8km) and has an area of over 295,000 km2 (the size of Arizona or much of France).

But there’s more. Mars is a dry planet with no water (as far as we know). This means you can’t measure the height of a mountain from sea level like we do, because there isn’t any sea to measure from. Olympus Mons is therefore measured from its base, which raises another question. What would happen if we took away the sea – would 8,848m Everest still be the highest mountain on Earth?

The answer is no. Mauna Kea (4,205m) on the island of Hawaii rises straight out of one of the deepest parts of the Pacific Ocean. At 10.2km it would be marginally higher than Everest, but still less than half the height of Olympus Mons. It’s also slightly steeper: while Olympus Mons has a base width of 600km, Mauna’s Kea’s base width is only 250km

But wait, there’s even more. With a height of 21km, Olympus Mons must be the highest mountain in the solar system, surely?


Olympus Mons isn’t even the highest mountain in the solar system. Apparently there’s a 529km-diameter asteroid flying around the solar system called Vesta, which has a 505km-diameter volcano on it called Rheasilvia.

My brain is currently exploding. How the hell do you measure the height of something that’s almost the same size as the thing it’s on? Cleverer people than me (people who are cunning enough to measure parts of an asteroid before it flies past them) claim that Rheasilvia is an incredible 22km high, narrowly pipping Olympus Mons to the title of highest mountain in the solar system. Or at least until some smart arse finds a bigger one.

So before I go back to climbing Ojos del Salado, the highest volcano on Planet Earth, here’s one more tweet with the diagram to end all diagrams.

Thanks to Bob Schelfhout Aubertijn for spotting some of these tweets, and therefore giving me the idea for this post.

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4 thoughts on “What’s the highest mountain in the solar system?

  • December 26, 2018 at 5:24 pm

    The only unique metric for the height of a mountain might be the distance of its summit from the centre of the body on which it stands.

    On earth Everest lies at a distance of 6,382.3 kilometres (3,965.8 miles) from the centere of the Earth while Chimborazo, in the Ecuador Andes reaches to a distance of 6,384.4 kilometres (3,967.1 miles).

    But as a mountaineer I might argue that it is the amount of climbing from the trail head.

  • December 26, 2018 at 5:33 pm

    Noteworthy; Rum Doodle which stands at a proud 40,000 and 1/2 feet!

  • January 1, 2019 at 9:20 pm

    I love thinking about this stuff, of course the only measure for me that matters is the amount of elevation you can ascend from the mountain’s true base. So mountains like Nanga Parbat, Rakaposhi, Dhaulagiri and Denali (if you don’t start from a glacier at 7900) are truly the greatest peaks to climb -I’m not really concerned with above sea level, distance from sea bottom, or distance from the core -I want to experience the biggest single rock I can fit in my vision.

  • January 8, 2019 at 11:29 pm

    Imagine trying to climb Olympus Mons.

    “is this the summit? nooo…” okay, is THIS the summit? noooo….”(ad infinitum)

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