While Mount Everest is the tallest mountain on Earth, Olympus Mons dwarfs it. Here's why:

* Height: Olympus Mons is about 21.9 kilometers (13.6 miles) tall, making it three times taller than Mount Everest.

* Type: Olympus Mons is a shield volcano, meaning it's formed by slow, flowing lava eruptions. This creates a broad, gently sloping structure unlike the sharp peaks of mountains on Earth.

It's important to note that "tallest" can be a tricky concept when we're talking about the universe.

* What's being measured: Are we measuring from the base to the peak, or from sea level? Since Mars doesn't have oceans, the "sea level" reference point isn't as straightforward.

* Other massive structures: There are other massive mountains in the solar system, like Rheasilvia on the asteroid Vesta, which is about 22 kilometers (14 miles) tall.

While Olympus Mons is the current "champion," it's entirely possible that there are even taller mountains out there, waiting to be discovered!