The Earth is the only known planet to have liquid water on its surface.
This description is about the unique nature of Earth. It explains that Earth is the only known planet in our universe that has liquid water on its surface. This makes Earth a special and unique planet, as liquid water is essential for life.
Earth is unique among known planets in having oceans of liquid water on its surface. It was long thought that Earth's water did not originate from the planet's region of the protoplanetary disk. Instead, it was hypothesized that water and other volatiles must have been delivered to Earth from the outer Solar System later in its history. Recent research, however, indicates that hydrogen inside the Earth played a role in the formation of the ocean. The two ideas are not mutually exclusive, as there is also evidence that water was delivered to Earth by impacts from icy planetesimals similar in composition to asteroids in the outer edges of the asteroid belt.