This video is a world map of the distant planet Neptune, is made from Hubble Space Telescope data taken from January 7-8, 2020.
The film reveals Neptune’s dynamic weather: white clouds of methane ice crystals swirling around the planet and two giant dark spots orbiting in the Northern Hemisphere. The bigger spot, a gigantic storm, is at the top of the planet; the smaller spot is below and to the right of its larger cousin. The planet completes a rotation every 16 hours.
Around the South Pole, the banding is concentrated where the wind blows from west to east, in the same direction as the rotation of the planet. Closer to the equator, also where the dark vortex is located, the wind blows from east to west, in the opposite direction to the rotation of the planet.
The gigantic vortex is 4,600 miles wide, wider than the Atlantic Ocean. The slightly smaller companion is 3,900 miles wide. The smaller feature may be a spin-off from the giant storm that later disappeared.
Credit: NASA, ESA, MH Wong (University of California, Berkeley), LA Sromovsky and PM Fry (University of Wisconsin-Madison), and J. DePasquale (STScI)
When NASA’s Voyager 2 spacecraft flew past Neptune in 1989 after an odyssey of nearly 3 billion miles, astronomers expected to see a close-up of a blue-green planet that looked as distinctive as a marble. Instead, they were shocked and intrigued to see a dynamic and turbulent world of swirling storms, including a giant feature called the Great Dark Spot, looming in Neptune’s far southern hemisphere.
The vortex was reminiscent of Jupiterthe legendary Great Red Spot, a monstrous storm that has raged for hundreds of years. Had this Great Dark Spot been brewing for as long? Or was it a more short-lived storm?
Scientists had to wait until 1994, when the Hubble Space Telescope and its keen eye looked at distant Neptune. The mysterious place had disappeared! This game of planetary peek-a-boo continued when Hubble saw another dark storm appear in Neptune’s northern hemisphere in 1995. Over the past three decades, Hubble has continued to observe the planet and see even more dark spots come and go.
Only Hubble can study these spots because it has the sharp vision to observe them in visible light. Hubble has shown that these storms live for a few years before disappearing or fading.
Researchers thought the current Northern Hemisphere giant storm was on its way to destruction when it mysteriously halted its southern journey and began drifting north. At the same time as the stunning reversal of the spot, a new slightly smaller dark feature appeared near its larger cousin and later disappeared. These startling events add to the mystery of this dynamic world.
Astronomers using NASA’s Hubble Space Telescope saw a mysterious dark vortex on Neptune drift abruptly away from probable death on the giant blue planet.
The storm, which is wider than the Atlantic Ocean, was born in the planet’s northern hemisphere and discovered by Hubble in 2018. Observations a year later showed that it was beginning to drift south towards the equator, where such storms are expected to emerge. the sight will disappear. To the surprise of observers, Hubble saw that by August 2020, the vortex changed direction and doubled back to the north. Although Hubble has been tracking similar dark spots for the past 30 years, this unpredictable atmospheric behavior is something new to watch.
Equally puzzling, the storm wasn’t the only one. In January this year, Hubble spotted another, smaller dark spot that temporarily appeared on its larger cousin. It may have been part of the gigantic vortex that broke off, drifted and disappeared on later observations.
“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. “This is a process that has never been observed. We’ve seen some other dark spots fade, and they’ve disappeared, but we’ve never seen any distortions, even though it’s predicted in computer simulations. “
This Hubble Space Telescope snapshot of the dynamic blue-green planet Neptune reveals a monstrous dark storm (top center) and the emergence of a smaller dark spot nearby (top right). The gigantic vortex, which is wider than the Atlantic Ocean, was traveling south toward certain doom from atmospheric forces on the equator when it suddenly made a U-turn and started drifting back north. Credit: NASA, ESA, STScI, MH Wong (University of California, Berkeley), and LA Sromovsky and PM Fry (University of Wisconsin-Madison)
The great storm, which is 4,600 miles in diameter, is the fourth dark spot Hubble has observed on Neptune since 1993. Two other dark storms were discovered by the Voyager 2 spacecraft in 1989 as it passed the distant planet, but they disappeared before Hubble could observe them. Since then, only Hubble has had the sharpness and sensitivity in visible light to track these elusive features, which appeared sequentially and then disappeared over a period of about two years each. Hubble discovered this latest storm in September 2018.
Bad weather
Neptune’s dark eddies are high-pressure systems that can form at mid-latitudes and then migrate to the equator. They remain stable due to the Coriolis forces, which cause storms in the Northern Hemisphere to rotate clockwise, due to the planet’s rotation. (These storms are different from Earth’s hurricanes, which turn counterclockwise because they are low-pressure systems.) But when a storm drifts towards the equator, the Coriolis effect weakens and the storm disintegrates. In computer simulations by different teams, these storms follow a more or less straight path to the equator, until there is no Coriolis effect to keep them together. Contrary to the simulations, the last giant storm did not migrate to the equatorial “kill zone”.
“It was really exciting to see this one behave the way it should and then suddenly stop and swing back,” said Wong. “That was surprising.”
Dark Spot Jr.
The Hubble observations also revealed that the enigmatic reversal of the dark vortex’s path occurred at the same time as a new blot appeared, informally referred to as “dark spot jr.”, Appeared. The newest site was slightly smaller than its cousin and measures about 3,900 miles across. It was near the side of the main dark spot facing the equator – the location some simulations show would cause a disturbance.
The smaller dark spot in this Hubble image may have been part of the giant storm that broke as the larger vortex approached the equator. Hubble discovered the gigantic storm in Neptune’s northern hemisphere in September 2018. The large feature is approximately 4600 miles wide. The estimated width of the smaller spot is 3,900 miles. Credit: NASA, ESA, STScI, MH Wong (University of California, Berkeley), and LA Sromovsky and PM Fry (University of Wisconsin-Madison)
However, the timing of the smaller spot’s appearance was unusual. “When I first saw the small spot, I thought the bigger one was being disturbed,” Wong said. ‘I didn’t think there would be another vortex because the little one is farther towards the equator. So it is in this unstable region. But we cannot prove that the two are related. It remains a complete mystery.
“It was also in January that the dark vortex stopped its movement and started moving north again,” added Wong. “Maybe by shedding that fragment, that was enough to keep it from going to the equator.”
The researchers are continuing to analyze more data to determine if any remnants of dark spot Jr. persisted through the remainder of 2020.
Dark storms are still mystifying
How these storms originated is still a mystery, but this latest giant dark vortex is the best studied to date. The storm’s dark appearance could be due to a raised dark cloud layer, and it could tell astronomers about the storm’s vertical structure.
Another unusual feature of the dark spot is the absence of bright accompanying clouds around it, which were present in Hubble images taken when the vortex was discovered in 2018. Apparently the clouds disappeared when the vortex stopped its journey south. The bright clouds form when the airflow is disrupted and directed up the vortex, likely causing gases to freeze into methane ice crystals. The lack of clouds could reveal information about how spots evolve, researchers say.
Reflection on the outer planets
Hubble captured many of the images of the dark spots as part of the Outer Planet Atmospheres Legacy (OPAL) program, a long-term Hubble project led by Amy Simon of NASA’s Goddard Space Flight Center in Greenbelt, Maryland, which annually captures world maps of the outer planets of our solar system when they are closest to Earth in their orbits.
OPAL’s main goals are to study long-term seasonal changes, as well as to capture relatively temporary events, such as the appearance of dark spots on Neptune or possibly Uranus. These dark storms may be so fleeting that some of them have appeared and faded in the past during perennial gaps in Hubble’s observations of Neptune. The OPAL program ensures that astronomers do not miss any other.