same blue

LITIrwin et al. (MNRAS 527, 11521, 2024) reprocessed Hubble STIS and Gemini data and found Uranus and Neptune are both a similar greenish blue. Neptune is only slightly bluer, because its ~2-bar haze layer (Aerosol-2) has about half the opacity of Uranus's, so light goes deeper and more red is absorbed by methane. The deep-azure Neptune of the Voyager 2 releases was contrast-enhanced. Uranus is greener at solstice: less polar methane and more brightly scattering methane-ice haze.

MODELEach planet is a two-layer reflector: haze (grey, opacity τ) over a methane column; halving the haze lets light travel deeper (path factor 1.4, my choice) that absorbs red with a smooth shape I chose (not the real CH₄ band list). Colours come through CIE with Bradford under a 5772 K Sun. The "Voyager" button applies a contrast stretch to show how the old blue was made. Nesting: an orange methane-absorbed red core, a purple dark-spot ring, a green Uranus, yellow sunlight, the blue Neptune, the void.

Voyager 1989 stretchUranus solstice

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