For starters, Neptune and Uranus are basically the same size: Both worlds are just over 30,000 miles (50,000 kilometers) wide, and Uranus is only a measly 900 miles (1,500 kilometers) larger in diameter than Neptune. Their masses are also about the same: Uranus is some 14 times the mass of Earth, while Neptune is about 17 times the mass of Earth.
Being ice giants, both planets are primarily composed of elements heavier than hydrogen and helium, such as oxygen, carbon, nitrogen, and sulfur. Although the tippy-tops of both worlds’ atmospheres are predominately hydrogen, helium, and methane, their mantles are chock-full of water, ammonia, and (again) methane.
From their sizes to their masses to their atmospheric compositions, the solar system’s ice giants share many properties with one another. So, it’s no surprise that their differing color schemes have long left astronomers scratching their heads.
Modeling shades of blue
Although the ice giants’ compositions are nearly the same, the new research describes how Uranus has more haze in its upper atmosphere than Neptune does, which gives Uranus a slightly whiter tint. According to the new model, if neither planet had any such haze, they would be almost exactly same shade of blue.
Unlike past models, the new model looked at the ice giants through a wide range of wavelengths, corresponding to numerous atmospheric layers. It also moved the haze particles deeper into the planets’ clouds, which, before now, researchers thought was a region that only contained layers of methane and hydrogen sulfide ices.