A volcano in Ecuador called Chimborazo sits closer to outer space than Mount Everest does, not because it is taller, but because the Earth bulges at the equator and Everest, further from that bulge, is actually deeper inside the planet.

The mountain is Chimborazo, a long-quiet volcano in the Andes of Ecuador, and the claim about it is true: its summit is the point on the surface of the Earth that sits farthest from the planet’s centre. Farther than the summit of Mount Everest, by about two kilometres. This is not because Chimborazo is taller. Measured the ordinary way, from sea level, it is more than two and a half kilometres shorter than Everest. It wins on a different measurement entirely, and the reason is the shape of the Earth.

Everest is the highest point above sea level. Chimborazo is the point on Earth’s surface farthest from the centre of the planet. Those are two different titles, and they go to two different mountains.

The numbers

The figures are close, which is part of what makes the result surprising. Chimborazo’s summit sits about 6,384.4 kilometres from the centre of the Earth. Everest’s summit sits about 6,382.3 kilometres from the centre. The gap between them is roughly 2.1 kilometres, in Chimborazo’s favour.

Above sea level the ranking flips. Everest reaches 8,848 metres, while Chimborazo reaches about 6,263 metres, around 2,585 metres lower. The thing that closes that large gap, and then reverses it, is where each mountain sits on the planet. Chimborazo is about one degree south of the equator. Everest is nearly 28 degrees north of it.

Why the Earth bulges

The Earth is not a sphere. It spins, and the spin throws its mass outward at the middle, so the planet is wider around the equator than it is from pole to pole. The shape has a name, an oblate spheroid, and the size of the effect is larger than most people expect.

Sea level at the equator is about 6,378 kilometres from the centre of the Earth. Sea level at the poles is about 6,357 kilometres from the centre. That is a difference of roughly 21 to 22 kilometres, built into the ocean itself before any mountain is added on top.

A mountain near the equator therefore starts with a head start of around twenty kilometres over a mountain near the poles, simply because the ground it stands on is already farther out. Chimborazo, sitting almost exactly on the bulge, collects nearly all of that advantage. Everest, well to the north, collects much less. Twenty-odd kilometres of head start is more than enough to overcome the roughly two and a half kilometres by which Everest is the taller mountain.

What “closest to space” actually means

It is tempting to turn this into a statement about being closest to space, and the United States National Oceanic and Atmospheric Administration does describe Chimborazo’s summit as the closest point on Earth to the stars. That is fair in one specific sense: of all the ground you can stand on, Chimborazo’s peak is the farthest from the core, and so the farthest out into the surrounding space.

It needs one clarification, though, because it is easy to misread.

Being farthest from the centre is not the same as being highest in the air. Everest still stands more than two and a half kilometres higher above sea level, with thinner air, lower pressure, and a harder climb for the lungs. If you mean highest above mean sea level, Everest wins. If you mean farthest from Earth’s centre, Chimborazo wins. The two questions sound like one, and they are not.

Three ways to be the tallest

Tallest is not a single fact.

It depends on where you start measuring. From sea level, the tallest mountain is Everest. From its own base, the tallest is Mauna Kea in Hawaii, which rises more than ten kilometres from the floor of the Pacific to its summit, though most of that is underwater. From the centre of the Earth, the tallest is Chimborazo. Each answer is correct, and each is answering a slightly different question.

Chimborazo is not even alone in beating Everest this way. Because the bulge lifts the whole equatorial region, more than two dozen other summits, most of them in the Andes, also sit farther from the centre of the Earth than Everest does. Chimborazo is just the farthest of them, and only by a slim margin over its closest rival, Huascarán in Peru. The record holds. It simply belongs to a different question than the one most people think they are asking.