Uranis.
Planet earth has an animal that starts with the letter z. Zebra starts with the letter z and is on planet earth. There are a few microrganisms that start with the letter z also.
No planet so far known, begin with the letter O.
Uranus is the planet that starts with the letter "U" in our solar system.
Earth
Uranus
Heliatrobe
Rover
Yes, there is a planet called Mars that starts with the letter "M".
Jupiter
Uranus
Globe
Yes, there is a planet that starts with the letter "R" and it is called "Mars." Mars is the fourth planet from the sun in our solar system and is known as the "Red Planet" due to its reddish appearance.