We have better maps of Mars than of the ocean floor
About 80% of Earth's ocean floor remains unmapped at high resolution. We have detailed satellite radar maps of the entire surface of Mars at around 20-metre resolution, but the ocean floor — lying under kilometres of water that blocks radar — must be mapped by ship-based sonar, a slow and expensive process. As of 2024, only about 20–25% of the seafloor has been mapped with ship-based sonar at 100-metre resolution. The ocean covers 71% of Earth's surface, meaning more of our own planet is unknown than the surface of our nearest neighbour in space.
It's counterintuitive that we know more about another planet than about Earth itself. The ocean's impermeability to our best remote-sensing tools makes it the largest unexplored territory on the planet we live on.
“We have better maps of Mars than of Earth's ocean floor. About 80% of the seafloor remains unmapped. More of our own planet is unknown than the surface of a neighbouring world. 🌊🔭 #OddlyHuman”