Do we know less about the sea than our solar system?

Yes, it is often said that we know less about the ocean depths than we do about the surface of other celestial bodies in our solar system. While we have extensively studied the moon and Mars through various missions, only about 20% of the ocean floor has been mapped in detail. The complexities of marine ecosystems and the challenges of deep-sea exploration further contribute to our limited understanding of the oceans compared to our knowledge of space.