Scientists Explain Why Ice Giants Uranus and Neptune Have Different Shades of Blue

Ice Giants: Scientists Identified Why Uranus and Neptune Have Different Shades of Blue — Neptune as seen from Voyager 2 from 4.4 million miles Unsplash/NASA

Uranus and Neptune are the ice giants in the Solar system that glow slightly different shades of blue. Scientists believe that they have already identified what caused Uranus to appear paler and Neptune to have a deeper, cobalt hue.

Researchers from the University of Oxford said that the answer lies in a haze layer in the atmosphere, which is two times thicker in Neptune. Study lead author Patrick Irvin said that this layer is called the Aerosol-2, which looks whitish at visible wavelengths and acts to lighten Uranus, which explains why the seventh planet in the Solar system has a paler shade of blue compared to Neptune.

(Photo : Unsplash/NASA)
Neptune as seen from Voyager 2 from 4.4 million miles

What Makes Uranus and Neptune Blue?

According to NASA Cosmos, Uranus and Neptune were unknown to ancient astronomers when the telescope was not yet invented because both planets are difficult to see using the naked eye. Uranus has blue-green, turquoise color, while Neptune sports an indigo color.

Both ice giants have hydrogen, helium, and methane in their atmospheres, although scientists think that hazes formed from other chemicals also exist in other altitudes of the planets. Uranus and Neptune contain deep atmospheres of molecular hydrogen, vast internal oceans of water, methane, and ammonia ices that melted due to high temperatures

Cloud bands and winds on Uranus are lined parallel to the planet's equator controlled by the planet's rapid spinning rather than the Sun's heat. Despite receiving the least amount of sunlight, Neptune's atmosphere is surprisingly active and dynamic as large storms and high-speed winds can be seen in its atmosphere.

The methane in their atmospheres makes them appear blue, albeit with different shades. Methane absorbs light at 600nm, which is at the red end of the color spectrum but reflects blue. But now, the question is - why do these ice giants have different shades of blue.

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Atmospheric Compositions of Ice Giants Give Them Different Hue

Researchers of the new study, titled "Hazy Blue Worlds: A Holistic Aerosol Model for Uranus And Neptune, Including Dark Spots" published in Earth and Planetary Astrophysics, created models of the atmospheres of Uranus and Neptune using the data from the Hubble Space Telescope, Voyager 2, and ground-based observations.

According to the researchers, the visible and near-infrared spectra of the atmospheres of the ice giants have long fascinated scientists, MailOline reported. Both planets have the same atmosphere with similar tropospheric temperatures.

Researchers explained that their models showed that Uranus has a thicker atmosphere than Neptune. That is why the former appears to have a paler blue color to the human eye than the latter.

Naomi Rowe-Gurney, a researcher at NASA's Goddard Space Flight Center whose focus is the atmospheres of the ice giants, told New Scientist that comparing the color of the two ice giants is rare. The authors of the study said that future observations would help answer the remaining questions and hopefully, the James Webb Space Telescope could uncover these mysteries during the planned observations for both planets.