Why Did Neptune's Dark Vortex Change Its Direction?

Neptune is the distant ice giant planet that also has its storms like Jupiter. Recently, there have been reports that one of its vortices is turning back its direction to the polar region after migrating to the equator.

According to ScienceAlert, astronomers are still unsure how and why Neptune's storm is changing its direction. But they said that figuring it out will give them more information on the atmospheric dynamics of Neptune.

Neptune's Dark Vortex Changes Its Direction

Neptune is hard to observe because of its distance equivalent to 3 times the distance of Earth from the Sun. But thanks to Voyager 2 that made its flyby on Neptune in 1989, scientists were able to discover two storms on the ice giant. Since then, Hubble has observed and tracked four more storms, known as Dark Spots, because of their darker hue than the planet's atmosphere.

The storms have almost similar behavior in which they appear in mid-latitudes, hang around for two years, and migrate to the equator before dissipating. Another dark spot would soon appear after four to six years.

However, the fourth dark spot named NDS-2018 observed by the Hubble is different from the other dark spots. Phys.org reported that this dark spot is wider than the Atlantic Ocean and started drifting toward the equator, where it is expected to disappear like its predecessors.

But much to everyone's surprise, the Hubble spotted the dark spot to have changed its course by August this year, reversing back to the polar region. After 30 years of observing the vortices on Neptune, this is the first time that they have observed such rare and unpredictable atmospheric behavior on the ice giant.

"It was really exciting to see this one act like it's supposed to act, and then all of a sudden, it just stops and swings back," said Michael Wong, a planetary scientist of the University of California, Berkeley. "That was surprising."

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Dark Spot Jr. Might Know the Answer

The reversal of path of the dark spot seems to coincide with the appearance of Dark Spot Jr. This new spot on Neptune is similar to its cousin but slightly smaller, which measures about 3,900 miles across, located near the main dark spot that faces the equator where disruptions usually occur.

"When I first saw the small spot, I thought the bigger one was being disrupted. I didn't think another vortex was forming because the small one is farther towards the equator. So it's within this unstable region. But we can't prove the two are related. It remains a complete mystery," Wong said.

The researchers said that there is more to know about Neptune's dark spots, which are empty clouds, unlike those on Satur and Jupiter. The clouds detected are just fluffy white clouds around the edges due to gases freezing into methane like ice crystals.

The next time the Hubble swings past Neptune, it would be interesting to know what NDS-2018 has been since last observed. The researchers presented their research during the 2020 Fall Meeting of the American Geophysical Union.