Neptune was discovered in 1846, but the last of the gas giant planets is not finished giving up its secrets. Astronomers using the Hubble Space Telescope (HST) have reporting finding a dark spot in the atmosphere surrounding the world, where one had never before been seen.

This dark vortex is a high-pressure system in Neptune's gaseous layer, driving atmospheric components upward. This action forms bright, pancake-shaped clouds which were first spotted by amateur astronomers in July 2015. Almost immediately, professional astronomers suspected a dark, unseen companion was driving the formation of the pancake-shaped clouds.

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

Now, that theory has been confirmed by researchers using the most famous of the space-based observatories. This marks the first time one of these features has been discovered on Neptune since the turn of the century.

"When NASA's Voyager 2 spacecraft flew by Neptune in 1989, astronomers were surprised to see such a gaping, dark hole at southern latitudes in the giant planet's cyan-colored atmosphere. The dark spot later disappeared. But the Hubble Space Telescope captured a new northern dark spot of comparable size in 1994," the HubbleSite reports.

The dark vortex was imaged by professional astronomers on May 16, 2016. The region is as long as the width of the continental United States. The HST is the only observatory in, or above, the world able to detect these dark vortices traveling around the distant planet, sitting at the edge of the solar system.

Large storms on Jupiter can last for several decades or centuries, as they slowly evolve over time. However, similar systems on Neptune are short-lived, and show great diversity in their life spans, sizes and shapes. This most distant world in our solar system is home to the highest wind speeds ever recorded anywhere in our family of planets.

Astronomers hope that by studying this newly discovered vortex, they can learn more about how such systems form, change over time and eventually dissipate. This data could also provide new insights into the inner workings off the atmosphere of Neptune.

Neptune revolves around the sun at a distance 30 times greater than that traced out by our home world, taking nearly 165 years to complete a single journey around our parent star.

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