Neptune and Uranus are so similar that scientists sometimes refer to the distant ice giants as planetary twins.

But these ice giants have one major difference: their color.

New observations from space and ground telescopes have revealed the reason for this difference. The farthest planets from the sun in our solar system, Neptune and Uranus, have the same sizes, masses, and atmospheric conditions.

Looking at the two planets side by side, which became possible after NASA's Voyager 2 spacecraft flew by in the 1980s, Neptune has a bright blue appearance and Uranus is pale sky blue.

Astronomers used the Gemini North telescope, NASA's infrared telescope, both in Hawaii, and the Hubble Space Telescope to create a model that can match the observations of Neptune and Uranus.

Scientists acknowledged that the excess haze accumulation in Uranus's atmosphere gives it a lighter appearance, this haze is thicker on Uranus than the similar atmospheric layer on Neptune, so it whitens Uranus's appearance from our perspective.

Without this haze in either planet's atmosphere, astronomers believe both planets would be almost identical in blue color.