A dark storm on Neptune changed direction abruptly and began to walk away from near-certain death, mysterious astronomers.
NASA’s Hubble Space Telescope first saw the vortex in 2018. A year later, the storm began to drift south towards Neptune’s equator, following the path of several storms in front of it. Usually, these dark spots on Neptune live for a few years before disappearing or fading. However, the storm mysteriously stopped moving south and made a sharp u-turn, drifting north again. At the same time, astronomers saw a second, smaller dark spot on the planet.
They theorize that this smaller “cousin” storm could be part of the original vortex that broke off and drifted away.
Related: Birth of ‘Great Dark Spot’ Storm on Neptune seen for the first time (photo)
“We are excited about these observations because this smaller dark fragment may be part of the dark spot disruption process,” said Michael H. Wong of the University of California at Berkeley in a NASA statement. “This is a process that has never been observed. We have seen some other dark spots fade and they have disappeared, but we have never seen anything distorted, even though it is predicted in computer simulations.”
Although Hubble has been tracking similar storms on Neptune for the past 30 years, astronomers have never seen such unpredictable atmospheric behavior.
The current storm, which is 7,400 miles (7,403 kilometers) wide (larger than the Atlantic Ocean), is the fourth darkest place Hubble has tracked since 1993. These storms are high-pressure systems that rotate clockwise as a result of the planet’s rotation (unlike hurricanes on Earth, which are low-pressure systems that rotate counterclockwise).
As storms drift towards Neptune’s equator, the Coriolis effect that typically keeps them stable begins to weaken and the storm disintegrates. But unlike storms observed in the past and computer simulations showing that storms follow a more or less straight path to the equator, this last vortex did not migrate to this “death zone.”
“It was really exciting to see this one behave the way it should act and then suddenly stop and swing back,” Wong said in the same NASA statement. “That was surprising.”
It was also surprising to see a smaller storm that may have been aborted by the larger vortex. Astronomers informally call the smaller storm “dark spot jr.” This “jr.” is still quite large and stretches for 6,276 km. While researchers can’t prove that the smaller storm broke off from the larger one, Wong said it was possible that shedding that fragment was enough to keep the larger storm from continuing towards the equator.
This latest giant storm on Neptune is the best studied to date on Earth. For example, when Hubble first saw the storm in 2018, the telescope saw bright accompanying clouds around the vortex. Those clouds are now gone, disappeared when the storm stopped drifting south. It is possible that the absence of these clouds may reveal some secrets about how the dark spots evolve.
There’s still a lot of mystery surrounding storms on Neptune, but NASA’s Outer Planet Atmospheres Legacy (OPAL) program is poised to crack those mysteries. But for now, astronomers will keep their eyes on this mysterious dark spot on Neptune.
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