The planet that has completed less than one revolution around the sun in the last 100 years is Neptune.

Here's why:

* Neptune's Orbital Period: Neptune takes approximately 165 Earth years to complete one orbit around the sun.

* Time Since Last Revolution: Since Neptune's orbital period is much longer than 100 years, it has not finished a full revolution around the sun in the last century.

Let me know if you have any other questions about the solar system!