How does a volcano on Mars differ from one on Earth?
The largest volcano in the Solar System is found on Mars. It’s called Olympus Mons. It absolutely enormous. It’s equivalent in size to the state of Arizona. The reason why that volcano—and others on Mars—is so big is because on Mars there’s no plate tectonics. A volcano like Hawaii is a hot spot volcano. What happens at Hawaii is there’s a stream of hot magma that’s focused in one place. And we have plates that move over the top of that hot spot on the Earth. Because that plate is moving over the top of it, you have a line of volcanoes that are downstream of it. On Mars there’s no plate tectonics. So everything that forms in that one hot spot is built up in one place. Why are there no plate tectonics on Mars? It’s actually because of the size—it’s a smaller planet. Mars is two-thirds the size of the Earth. So basically it’s cooled to a point where there’s nothing that’s driving flow within the mantle anymore. What was it like studying Mars after working with Earth rocks? It’s been an i
