(ORDO NEWS) — Observations from the Hubble Space Telescope, NASA’s Infrared Telescope, and the Gemini Observatory show that the excess haze on Uranus makes it paler than Neptune, and the dark spots are caused by the darkening of the second, deeper cloud/haze layer.
The researchers have developed a single atmospheric model that matches observations of both planets. It shows that the excess haze on Uranus accumulates in the planet’s stagnant, sluggish atmosphere and makes it a tone lighter than Neptune.
The model also shows the presence of a second, deeper layer that, when darkened, could explain the appearance of dark spots in these atmospheres, such as the famous Great Dark Spot observed by Voyager 2 in 1989.
Neptune and Uranus have a lot in common – they have similar masses, sizes and composition of the atmosphere, but their external manifestations are noticeably different. In the visible wavelength range, Neptune is clearly more blue than Uranus.
If there were no haze in the atmospheres of Neptune and Uranus, both planets would look almost equally blue.
The team model consists of three layers of aerosols located at different heights. The key layer that affects colors is the middle layer, which is a collection of haze particles (called the aerosol-2 layer in the paper), which is thicker on Uranus than on Neptune.
The team suspects that on both planets, methane ice condenses on particles in this layer, drawing them deeper into the atmosphere as methane snow.
Because Neptune has a more active, turbulent atmosphere than Uranus, the team thinks Neptune’s atmosphere is more efficient at whipping methane particles into a layer of haze and producing what’s called snow. This removes most of the haze and makes it thinner on Neptune than on Uranus.
To create the model, the team analyzed a data set of planets in the ultraviolet, visible, and near-infrared wavelengths (0.3 to 2.5 micrometers) taken by the NASA/ESA Hubble Space Telescope, NASA’s infrared telescope located at the summit of Maunakea on Hawaii, and the Gemini North Telescope, also located in Hawaii.
In addition, the model helps explain the dark spots that are seen occasionally on Neptune and more sporadically on Uranus.
Although astronomers were already aware of the presence of dark spots in the atmospheres of both planets, they did not know which layer of aerosol caused these spots and why the aerosols in these layers are less reflective.
The team’s study shows that the darkening of particles in the deepest layer of the model results in dark spots very similar to those seen on Neptune and sometimes Uranus.
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