Jupiter may have the most famous storm in the solar system, but that doesn’t mean all the fun is done, and Neptune has just presented scientists with a dream.
While storm vortices are not unusual for the distant ice giant, it is the first time it has been observed to turn toward the polar region after migrating to the equator.
Astronomers still don’t know exactly how or why he managed to change course, but finding out could tell us more about Neptune’s atmospheric dynamics.
In fact, Neptune is quite difficult to see compared to the other planets in the solar system. It is located at sunrise, at an average distance of 30 times that between the Earth and the Sun, which makes it difficult to find out many details. So it wasn’t until 1989, when Voyager 2 flew over, that two storms were discovered on Neptune.
Since then, Hubble, the only instrument capable of doing so, has observed and tracked four of these more storms, called dark spots, because of their darker tone than the surrounding atmosphere.
In general, their behavior has been quite similar: they appear at mid-latitudes, remain for about two years as they migrate to the equator, and then dissipate. Then, four to six years later, another appears.
This storm, however, the fourth observed by Hubble, called NDS-2018, has been the exception.
“It was really exciting to see that this one was acting the way it was supposed to act, and suddenly it just stops and backs away,” said planetary scientist Michael Wong of the University of California, Berkeley. “It was amazing.”
NDS-2018, as its name suggests, was first discovered in 2018. At that time, it had been growing for several years and measured about 11,000 kilometers (6,800 miles) in diameter.
When Hubble observed it again in January 2020, it behaved as expected, migrating south to the equator from mid-northern latitudes.
As it migrated, the Coriolis effect that kept the storm stable at mid-latitudes was expected to weaken and gradually disappear when the storm reached the equator. Then, according to previous simulations and observations, NDS-2018 should have disappeared into oblivion.
But those January observations revealed something strange: a slightly smaller dark spot like a miniature version of the larger storm. NDS-2018 was, at that time, about 7,400 kilometers in diameter. Dark Spot Jr., as the nickname was called, was about 6,275 miles in diameter.
Then, in August of this year, when Hubble took another look at NDS-2018 (it’s a very busy telescope and can’t stare at Neptune all the time), the storm was heading north again. . Punt Fosc Jnr. he had disappeared.
(NASA, ESA, STScI, MH Wong / UC Berkeley and LA Sromovsky and PM Fry / University of Wisconsin-Madison)
“We are excited about these observations because this smaller dark fragment is potentially part of the dark spot disruption process,” Wong said.
“This is a process that has never been observed. We have seen some other dark spots fade away and have disappeared, but we have never seen anything interrupted, although it is predicted in computer simulations.”
It is impossible to know exactly what happened, but the appearance and subsequent demise of Dark Spot Jr. it could be a clue. On the one hand, it was near the side of NDS-2018 that was closer to the equator. According to the simulations, if something interrupted a storm of Neptune, it would happen here.
The fact that Dark Spot Jr. appearing when he did could also be a clue.
“When I first saw the small point, I thought the larger one was being interrupted. I didn’t think another vortex would form, because the smaller one is further away towards the equator. So it’s inside. of this unstable region. But we cannot prove that the two are related. It remains a complete mystery, “Wong said.
“It was also in January that the dark vortex stopped its movement and began to move north again. Perhaps launching this fragment was enough to prevent it from moving toward the equator.”
There are still many things we do not know about the dark spots of Neptune. They are quite empty of clouds in the middle, compared to the storm vortices of Saturn and Jupiter. The clouds we can detect are white, spongy clouds that appear around the edges, probably as a result of the freezing of gases in methane ice crystals as they rise from lower altitudes.
In this score, NDS-2018 provides another mystery: its fluffy white clouds disappeared when the storm changed direction.
Researchers say this could reveal more information about how Neptune’s storms evolve. Meanwhile, they’re also looking more closely at available data to see if they can find more information about Dark Spot Jr., to see if the smaller storm, or chunks of it, may have hung a little longer.
When Hubble tilts its bright eye toward Neptune as part of the Outer Planet Atmospheres Legacy program, scientists will be very interested to see what NDS-2018 does.
The team’s research was presented at the Fall 2020 meeting of the American Geophysical Union.