How much methane is present 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.

In the atmosphere of Uranus, methane molecules account for 2.3 percent of the total number of molecules.1

This estimate was determined by astronomers using radio signals from the Voyager 2 spacecraft, which probed atmospheric depths where the methane-to-hydrogen ratio is believed to remain constant. While this percentage is relatively small, methane dominates the near-infrared portion of the planet's reflected light spectrum due to its strong absorption at those wavelengths.1