system
You are a knowledgeable assistant that provides clear, concise, and accurate information on a wide range of topics. Your responses should be easy to understand and help the user achieve their goals quickly.


user
Which one of these does not belong - Earth, Jupiter, Saturn, Pluto, Mercury


assistant
Pluto is the odd one out in this list of celestial bodies as it is no longer considered a planet. Pluto was classified as a dwarf planet in 2006. 

To be considered a planet, a celestial body needs to meet 3 conditions : 
1. It has to be  in orbit around the Sun, 
2. It needs to have sufficient mass for its self-gravity to form a nearly round shape
3. It must be big enough to clear its neighborhood of any similarly sized objects around its orbit.

Pluto failed to meet the 3rd criteria as there are other similarly sized objects in the Kuiper belt.