The atmospheres of Uranus and Neptune are remarkably similar in composition, consisting of mostly hydrogen, with some helium and a little methane, which gives them both their blue colour. Yet despite this, the two planets are noticeably different in hue, with Neptune a deep royal blue while Uranus is a pale turquoise.

After years of wondering what could be causing the difference, a new set of observations from the Gemini Observatory might finally explain it.

By looking at the planets in many wavelengths, astronomers were able to observe the different layers of the two planets’ atmospheres. Both are covered by a layer of haze, which the new study found extends much deeper than previously thought. It also showed that Uranus’s haze is much thicker, effectively whitening the planet.

“We hoped that developing this model would help us understand clouds and hazes in the ice giant atmospheres,” commented Mike Wong from the University of California, who took part in the study. “Explaining the difference in colour between Uranus and Neptune was an unexpected bonus.” www.gemini.edu