STORMS have clouded Uranus’s normally placid face. In the past year, the gas planet has played host to huge cloud systems so bright that even amateur astronomers can see them from Earth – and their cause is a mystery.
“We have no idea. It’s very unexpected,” says Imke de Pater at the University of California, Berkeley.
De Pater observed Uranus on 5 and 6 August, 2014, and was surprised to spot unusually bright features, the hallmark of clouds condensing in the planet’s upper atmosphere. “It was brighter than anything we had ever seen in Uranus’s atmosphere before,” she says. The planet’s weather generally picks up at its spring and autumn equinoxes every 42 years, when the sun shines on the equator. But the last equinox was 7 years ago, so the recent spike in activity is difficult to explain.
De Pater’s group spread the word, and amateurs around the globe trained their telescopes on Uranus. Coincidentally, the amateurs spotted a storm that de Pater had imaged at a different wavelength on 5 August. Using the Hubble Space Telescope, de Pater and her colleagues saw storms spanning a variety of altitudes (arxiv.org/abs/1501.01309), which could be linked to a vortex deep in Uranus’s atmosphere.