Neptune and Uranus are so similar that scientists sometimes refer to these distant planets as “twins”. However, these two giant ice planets have a significant difference in color.
Recent space observations and telescopic data have revealed the reason behind this color discrepancy. Neptune and Uranus share similar sizes, masses, and atmospheric conditions.
Neptune and Uranus have nearly identical blue colors.
After NASA’s Voyager 2 spacecraft flew past these two planets in the 1980s, scientists discovered that Neptune has a bright blue appearance, while Uranus appears lighter blue.
Astronomers utilized the Gemini Telescope and NASA’s Infrared Telescope Facility, both located in Hawaii, as well as the Hubble Space Telescope to create a model that could match the observations of Neptune and Uranus.
Scientists determined that there is a layer of haze accumulating in the atmosphere of Uranus. This haze layer on Uranus is thicker than that on Neptune, which is the reason Uranus appears lighter in color.
Without this haze in the atmospheres of both planets, astronomers believe that Neptune and Uranus would have nearly identical blue colors. The study was published in the Journal of Geophysical Research: Planets.
Previously, to understand this difference, scientists often focused on the upper parts of the planets’ atmospheres at specific light wavelengths.
The lead author of the new study, Patrick Irwin, a Professor of Planetary Physics at the University of Oxford (UK), stated: “This is the first model that fits observations of sunlight reflected from ultraviolet to near-infrared wavelengths.
This is also the first discovery explaining the visible color differences between Uranus and Neptune.”
The model also explored deeper atmospheric layers, including haze particles, in addition to methane clouds and hydrogen sulfide ice. The research team analyzed three haze layers at different altitudes on Uranus and Neptune. The middle layer of haze particles had the greatest impact on color.
On both planets, the middle layer is where methane ice transforms into methane snow. Neptune has a more turbulent atmosphere than that of Uranus. Therefore, methane particles and snow prevent haze from forming on Neptune.
Scientists believe that this model may also help explain why dark spots appear on Neptune but are less common on Uranus. The research team noted that it is likely due to the deepest atmospheric layer becoming darker, which is more visible on Neptune.
