Record-breaking Storm Activity on Uranus in 2014

TL;DR

In 2014, eight large storms, including the brightest ever observed, were detected on Uranus's northern hemisphere, revealing unexpected storm activity and atmospheric features despite prior expectations of decline.

Contribution

This study reports the first detection of a north polar haze and the observation of multiple large storms on Uranus after its 2007 equinox, using advanced telescopic imaging.

Findings

Detection of the brightest storm at 2.2 μm on Uranus.

Observation of a deep cloud feature at 32°N.

First identification of a north polar haze.

Abstract

In spite of an expected decline in convective activity following the 2007 equinox of Uranus, eight sizable storms were detected on the planet with the near-infrared camera NIRC2, coupled to the adaptive optics system, on the 10-m W. M. Keck telescope on UT 5 and 6 August 2014. All storms were on Uranus's northern hemisphere, including the brightest storm ever seen in this planet at 2.2 $\mu$m, reflecting 30% as much light as the rest of the planet at this wavelength. The storm was at a planetocentric latitude of $\sim$15$^{\circ}$N and reached altitudes of $\sim$330 mbar, well above the regular uppermost cloud layer (methane-ice) in the atmosphere. A cloud feature at a latitude of 32$^{\circ}$N, that was deeper in the atmosphere (near $\sim$2 bar), was later seen by amateur astronomers. We also present images returned from our HST ToO program, that shows both of these cloud features. We further report the first detection of a long-awaited haze over the north polar region.