While Mars has garnered attention for decades, there’s still a lot about it we don’t know. We know it has a core, but scientists are unsure how big it is or what it’s made of. It could be small and dense—made up of iron and nickel like our own core, or larger and made of several types of materials. Mars is often referred to as a dead planet, but it’s actually pretty active. It had active volcanoes just 50-100 million years ago, relatively recently in geologic terms, and researchers would love to know more about how they formed, and why they stopped erupting.