Hubble telescope discovers a storm on Neptune 20% earth's size

Credits: NASA, ESA, A. Simon (NASA
 Goddard Space Flight Center), and
M.H. Wong and A. Hsu (University
of California, Berkeley)

While its routine sweep of outer solar system, the Hubble telescope discovered a "dark vortex" in the clouds of Neptune, according to NASA. The American space agency jointly announced this discovery with Space Telescope Science Institute (STScI) on Thursday.

The storm as shown in the above image is huge. It spans 6,800 miles across and is 20% the earth's surface area. The storm is confined to the northern hemisphere of Neptune and is accompanied by a patch of bright white clouds. Such clouds are formed because the storm plows through the surrounding air high above the storm, cooling it off and causing it to freeze. In this case, the frozen material is most probably methane.
"These clouds are similar to the clouds that appear as pancake-shaped features when air is pushed over mountains on earth (though Neptune has no solid surface)", said STScI.
This is the fourth storm ever discovered on Neptune. While the storms on earth typically last for a few days or weeks, Neptune's dark vortex is expected to last for years. Currently, the longest running storm ever recorded is the great red spot on Jupiter that has been in existence for almost 400 years, however it is continuously shrinking.

Image of Neptune taken by Voyager 2
 in 1989 Credit: NASA/JPL 

Neptune is known for its dark storms. The first two were spotted by the Voyager 2 Spacecraft of NASA when it was flying past the gaseous giant back in 1989. The fourth and the latest one was discovered in September 2018, but was announced only this week.