The pictures released Thursday pleased space enthusiasts who described the scenes as "spectacular" and "fascinating." Many wanted to know what exactly was causing a giant white cap to "swirl" over Uranus' north pole and a new "mysterious dark vortex" to form at the top center of Neptune.
The space agency explained the planets' seasons, which are vastly different than Earth's and can span decades, may play a part in some of the bizarre atmospheric events.
The images were captured during NASA's yearly monitoring of the planets in our solar system.
“[These] observations are helping us to understand the frequency of storms, as well as their longevity,” Amy Simon, a scientist at NASA’s Goddard Space Flight Center, told Gizmodo. “That’s important because these planets are quite far from the Sun, so this will help constrain how they are forming and more about the internal heat and structure of these planets. Most of the extrasolar planets that have been found are this size of planet, though at all sorts of distances from their parent stars.”
This is the fourth time a dark spot has been seen hovering over the farthest planet from the Sun, according to NASA.
"Two other dark storms were discovered by the Voyager 2 spacecraft in 1989 as it flew by the remote planet," NASA added in an online statement, noting a University of California, Berkeley study estimated the spots pop up every four to six years or so.
This recent storm, which NASA measures at about 6,800 miles wide, was discovered in September 2018 as Hubble observed Neptune's northern hemisphere.
"It's unclear how these storms form. But like Jupiter's Great Red Spot, the dark vortices swirl in an anti-cyclonic direction and seem to dredge up material from deeper levels in the ice giant's atmosphere," said NASA, explaining the storm becomes even more prominent as it reaches a higher altitude.
Like Neptune, Uranus was experiencing a storm of its own.
A "bright stormy cloud cap" was seen hovering over the seventh planet from the Sun.
"Scientists believe this new feature is a result of Uranus' unique rotation. Unlike every other planet in the solar system," NASA explained. "Uranus is tipped over almost onto its side. Because of this extreme tilt, during the planet's summer, the Sun shines almost directly onto the north pole and never sets. ... This polar hood may have formed by seasonal changes in atmospheric flow."
As Uranus hits mid-summer, the "polar-cap region" is easier to spot.
“Back in 2007, there didn’t appear to be anything like this polar cap over the springtime pole. But as time progressed, a reflective band—whitish against Uranus’ blue hues—began to appear encircling the north pole. And now, 10 years on, that band has turned into a thick polar cap of aerosols that’s hiding the deeper polar region from view," astronomer Leigh Fletcher with the University of Leicester told Gizmodo.
NASA admits the "methane-ice cloud" surrounding the polar storm is still unclear.
"It is a mystery how bands like these are confined to such narrow widths because Uranus and Neptune have very broad westward-blowing wind jets," the agency added.