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Which gases are most abundant in Uranus's atmosphere?

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Images obtained by Voyager 2. — Uranus Two views of the southern hemisphere of Uranus, produced from images obtained by Voyager 2 on Jan. 17, 1986. In colours visible to the unaided human eye, Uranus is a bland, nearly featureless sphere (left). In a colour-enhanced view processed to bring out low-contrast details, Uranus shows the banded cloud structure common to the four giant planets (right). From the polar perspective of Voyager at the time, the bands appear concentric around the planet's rotational axis, which is pointing nearly toward the Sun. Small ring-shaped features in the right image are artifacts arising from dust in the spacecraft's camera.

The atmosphere of Uranus is composed primarily of molecular hydrogen and atomic helium. These two gases are the most abundant constituents of the planet's atmosphere.1

While hydrogen and helium dominate the composition, methane is also present, accounting for approximately 2.3 percent of the total number of molecules. Although methane is less abundant than hydrogen and helium, it plays a significant role in the planet's appearance by strongly absorbing light at near-infrared wavelengths.1

Other substances, such as water, ammonia, and hydrogen sulfide, are also thought to be present in the atmosphere, though they typically condense into clouds at depths below the visible layers. Additionally, trace amounts of acetylene and ethane have been detected as by-products of methane dissociation in the upper atmosphere.1