1.   - Venus is the only planet that rotates clockwise.

2.   Earth is the only planet in the solar system known to have liquid water on its surface.

3.   Ours is the only planet not capitalized, presumably because earthlings are modest.

4.   Pluto is the only planet in our solar system not yet visited by a NASA spacecraft developed by the Pasadena, Calif.-based JPL.

5.   Pluto is the only planet in the solar system that has never been visited by a spacecraft.

6.   Pluto is the only planet in the solar system yet to be visited.

7.   Pluto is the only planet in the solar system that has yet to be studied up close by a visiting spacecraft.

8.   Progress is also being made in devising an affordable mission to Pluto, the only planet in the solar system yet to be visited by spacecraft.

9.   Scientists recently concluded from meteorite evidence that dry Mars, the only planet in the habitable zone between Earth and Jupiter, had water in its distant past.

10.   Some three billion miles away, Pluto is the only planet in the system that has yet to receive a spacecraft from Earth.