Uranus and Neptune both have the blues. But different hues.

Uranus and Neptune both have the blues. But different hues. thumbnail

Neptune, Uranus, and Uranus are both ice-planets in the solar system. However, they have different shades of blue. Neptune has a brighter blue color than Uranus, which is a pale cyan. NASA astronomers have finally discovered why the two similar planets have distinct hues. The study , published last Wednesday in the Journal of Geophysical Research on Planets showed that haze particles can whiten a planet’s appearance, which could explain Uranus’s pale complexion.

Understanding the differences in color could help astronomers understand the environment on these two planets. Both worlds share many similarities, besides the differences in blue shades. Both worlds have similar atmospheric makeups, masses and sizes, each about 4x larger that Earth (if Earth were a nickel, Uranus or Neptune would be about the same size as a baseball).

Uranus and Neptune, which are nearly 2 million miles from Earth, make it difficult to learn about these two giant planets. And, unlike Mars, where the Perseverance rover is currently gathering data, these planets were only observed through a flyby with the spacecraft Voyager 2 almost 30 years ago. The team used data from several telescopes, including the Gemini North telescope, NASA Infrared Telescope Facility and the Hubble Space Telescope, to fill in the gaps. They then created an atmosphere model that resembles Neptune or Uranus.

[Related: We’re finally figuring out how Uranus ended up on its side]

Previous research on the atmospheres on both planets did not reveal the color difference because it was limited to Uranus and Neptune’s appearance at specific wavelengths. Methane, which absorbs sunlight’s red color and reflects blue light, is found in both atmospheres. The new model uses a wide wavelength spectrum to observe multiple layers of atmospheric atmosphere.

“This model is the first to simultaneously match observations of reflected sunlight at ultraviolet and near-infrared wavelengths,” Patrick G.J. Irwin, lead author of the study and a planetary physics professor at the University of Oxford, said in a NASA press release. “It’s also first to explain the visible color difference between Uranus .”

and Neptune.”

Uranus and Neptune both have the blues. But different hues.
A diagram of the atmospheres of Uranus and Neptune. The atmosphere of Uranus and Neptune is affected by the haze layer in the middle. International Gemini Observatory/NOIRLab/NSF/AURA, J. da Silva/NASA /JPL-Caltech /B. Jonsson

The new model revealed that the haze surrounding Uranus is thicker than Neptune’s, making Uranus appear lighter. Neptune’s atmosphere has a thin layer of haze, and it is more efficient at churning methane particles from the haze to create methane snow. Neptune is therefore more effective in reducing methane in its cloud, and its snow allows for more blue light to reflect in the atmosphere, which results in a strong blue color.

The researchers noted that both planets would have the exact same shade of blue if there was no haze. “We hoped that this model would help understand clouds and hazes within the ice giant atmospheres,” Mike Wong, an Astronomer at the University of California Berkeley, stated in a press release. “Explaining the color difference between Uranus & Neptune was an unexpected bonus !”

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