As the two ice giant planets farthest from the sun in the solar system, Uranus and Neptune are similar to twins in size, mass and atmospheric conditions, but don’t worry about being difficult to distinguish, because they have a very obvious difference: Neptune is more colored than Uranus. To be blue. Recently, scientists uncovered the reason behind the color difference between the two.
In the 1980s, when the NASA Voyager 2 spacecraft flew by Uranus and Neptune, it was found that Neptune had a blue appearance in the visible light band. In contrast, Uranus had a lighter blue-blue appearance, which puzzled scientists because Uranus and Neptune are about the same mass and size (the former). About 15 times the earth, the latter is about 17 times the earth), the composition and proportion of hydrogen (all over 80%), helium, and methane in the atmosphere are also almost the same. Why do the two show significantly different blues?
Scientists have suggested in the past that maybe Neptune’s methane absorbs so much red light that it looks bluer, but that doesn’t explain why Uranus, which has more methane, is less blue (2.3% methane in Uranus’s atmosphere, 1.9% methane in Neptune’s atmosphere) ).
After developing an atmospheric model based on observations from the Hubble Space Telescope, the IRTF Infrared Telescope, and the Gemini Northern Telescope, astronomers now finally know the reason: Uranus’s bluer looking bluer than Uranus is due to the slower atmospheric flow conditions and the accumulation of haze. Neptune is more “pale”.
In the model, the team said that the key to affecting the appearance of the two lies in the Aerosol-2 layer of the atmosphere, where methane ice usually condenses into methane snow and falls. Because Neptune’s atmosphere is more active and turbulent than Uranus, it can stir methane particles more and reduce fog. Haze, if neither Neptune nor Uranus had accumulated haze in their atmospheres, they would appear nearly identical in blue.
Uranus is a strange world. Its rotation axis is tilted at an angle of 97.77275°. It almost “lies” on the orbital plane and revolves around the sun. This planet has no internal heat, so it has the coldest atmosphere of all planets in the solar system.
Scientists will need to continue to rely on ground-based telescopes and Hubble Space Telescope data to study the two ice-giant planets, as there are currently no vehicles that can travel that far to see them up close.
However, NASA has proposed the next generation of large missions to investigate Uranus, and the observations may completely change astronomers’ understanding of the ice giant.
The new paper is published in the journal Geophysical Research: Planets.
(Source of the first image: NOIRLab)
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