Hubble Spies Dark Spot Erupt on Neptune

The new feature is driven by a powerful vortex accompanied by vast high-altitude clouds.

Neptune orbits the sun at the very edge of the solar system, and although it's technically known as an "ice giant" its atmospheric dynamics are far from frozen.

In recent observations of the azure planet, the Hubble Space Telescope followed up on ground-based observations to find a dark spot has appeared in the upper atmosphere. The spot is indicative of a vortex, or a high pressure region, which is accompanied by vast bright clouds that now tower over the swirling mass.

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This isn't the first time such a feature has appeared; similar features were observed during the Voyager 2 flyby in 1989 and by Hubble in 1994, but this is the first dark vortex to appear on Neptune in the 21st Century.

"Dark vortices coast through the atmosphere like huge, lens-shaped gaseous mountains," said astronomer Mike Wong, of the University of California at Berkeley, in a statement. "And the companion clouds are similar to so-called orographic clouds that appear as pancake-shaped features lingering over mountains on Earth."

Hints of the current vortex were noted by the W. M. Keck Observatory in Hawaii and amateur astronomers in 2015, who noticed the bright high-altitude clouds. However, it wasn't until Hubble zoomed in on the region that the dark vortex emerged. Typically, dark vortexes can only be seen in blue wavelengths and Hubble is the only telescope with high enough resolution to see the darkening and confirm that the bright clouds were indeed being caused by a vortex.

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Studying the emergence, speed and motion of Neptunian vortices help planetary scientists probe the mysterious planet's atmosphere. Vortices on Neptune appear and disappear on much shorter timescales when compared with anticyclones on Jupiter, for example. Why this is the case is a topic of much discussion.

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