Olympus Mons on Mars stretches 21.9 kilometers above the Martian datum—roughly two and a half times the height of Everest. That’s not a mountain. That’s a planetary blemish, a geological middle finger to everything we thought we knew about how big things could get.
Here’s the thing: Earth’s mountains are constrained by plate tectonics, erosion, and gravity that doesn’t mess around. Mars? Different rulebook entirely. Lower gravity means magma can pile up like cosmic Jenga blocks without collapsing under their own weight. Olympus Mons has been erupting on and off for hundreds of millions of years, each lava flow adding another layer to what’s essentially the solar system’s most overachieving volcano. The base spans 600 kilometers. You could fit the entire state of Arizona inside its footprint and still have room for brunch.
When Planets Forget How to Stop Building Mountains
But wait—maybe Mars isn’t even the most dramatic landlord in this celestial neighborhood.
Io, Jupiter’s pizza-faced moon, hosts a mountain called Boösaule Montes that peaks at 17.5 kilometers. Io’s surface gets kneaded like dough by Jupiter’s gravitational pull, generating enough tidal heating to power over 400 active volcanoes. The mountains there aren’t volcanic, though. They’re compressional ridges—tectonic wrinkles formed when Io’s crust gets squeezed like an accordion. South Boösaule Montes, measured by the Galileo spacecraft in 2001, rises so steeply it makes Everest look like a speed bump. The slopes hit angles of 40 degrees in places, which on a body with barely any atmosphere means rockfalls that go on for kilometers without air resistance to slow them down
Turns out the tallest peak in the solar system might actually be Rheasilvia Mons on the asteroid Vesta.
This central peak, sitting inside a 505-kilometer impact crater, climbs roughly 22 kilometers from the crater floor—though measuring “height” on an irregularly shaped asteroid gets philosophically weird fast. NASA’s Dawn mission mapped it in 2011, and the data suggested this wasn’t just tall; it was absurd. Vesta’s gravity is so weak you could probably jump off Rheasilvia’s summit and achieve escape velocity if you were having a particularly athletic day.
The Problem With Calling Anything the Tallest When Nobody Agrees on Sea Level
Venus contributes Maxwell Montes to this cosmic measuring contest—11 kilometers above Venus’s mean radius. That might sound modest until you remember Venus is a 460-degree hellscape with sulfuric acid clouds and atmospheric pressure that would crush a submarine. The Soviet Venera landers confirmed the elevation data in the 1980s before promptly melting into expensive scrap metal. Maxwell Montes sits in Ishtar Terra, one of Venus’s two continent-sized highlands, and nobody’s entirely sure if it’s volcanic, tectonic, or some nightmare hybrid of both.
Why Earth’s Mountains Are Basically Participation Trophies in This League
Mauna Kea in Hawaii measures 10.2 kilometers from its seafloor base to summit—taller than Everest if you’re willing to count underwater real estate, which geologists definitely are. But compared to Olympus Mons, it’s embarassing. Earth’s mountains erode, shift, crumble. Our planet is geologically hyperactive, constantly recycling its crust through subduction zones and weathering.
The solar system’s giants, meanwhile, are fossils—monuments to volcanic and tectonic processes that ran wild without Earth’s self-limiting mechanisms.
The tallest mountains out there aren’t shaped by the same forces that built the Himalayas. They’re products of lower gravity, absent erosion, and geological patience measured in billions of years. Olympus Mons will still be there long after Earth’s mountains have been ground into sand and recycled into new crust. Which is either humbling or depressing, depending on whether you’re an optimist about planetary timescales.
