Answer: Neptune

At a whopping average distance of 4.5 billion kilometers away from the Sun, the planet Neptune takes its sweet time completing each orbit around the fiery center of our solar system. How long exactly? A Neptunian year is just shy of a staggering 165 Earth years.

Since its discovery in 1846, Neptune has completed only one orbit around the Sun, finishing its first full barycentric orbit on July 11, 2011. Thanks to its lengthy orbit, we won’t be seeing Neptune in a similar position until 2176.

Solar orbit isn’t the only thing that’s particularly long on Neptune. The planet has an axial tilt similar to Earth’s and, as a result, experiences Earth-like seasonal changes, with seasons lasting for approximately 40 Earth years. If such an arrangement existed on Earth, many of us would only experience two seasons in our lifetimes.