Neptune Great Dark Spots

Figure 1 A massive dark storm [top centre] and the emergence of a smaller dark spot nearby [top right] are visible in this Hubble Space Telescope image of the dynamic blue-green planet Neptune. Credits: NASA

Neptune's weather is among the strangest in the solar system. The sun's eighth planet has the fastest winds of any planet, cutting through the atmosphere at speeds of up to 1,100 miles per hour, or 1.5 times the speed of sound. Scientists are still baffled as to why its atmosphere is so turbulent. Their most recent sighting of Neptune added to their confusion.

In 2018, the Hubble Space Telescope discovered a storm with a diameter of 4,600 miles. According to the most recent Hubble observations, it appears to have drifted toward the equator but then swooped back up north. It also has a smaller companion storm, dubbed Dark Spot Jr., which scientists believe is a piece of the main storm that broke off. These inky vortexes stand out against the planet's dizzying cerulean blue, but while they're beautiful to look at, their lifespans are brief, making them even more difficult to study.

Hubble observations also revealed that the dark vortex's perplexing path reversal happened at the same time as the appearance of a new spot, dubbed "dark spot jr." The new spot, which was about 3,900 miles across, was slightly smaller than its older sibling. It was near the side of the main dark spot facing the equator, which is where some simulations predict a disruption. The appearance of the smaller spot, on the other hand, came at an unusual time. “The astronomers  thought the bigger one was being disrupted when they first saw the small spot," but "Because the small one is closer to the equator, I didn't think another vortex was forming." So it's in this tumultuous area. However, they are unable to establish a link between the two. It's still a complete mystery to me. "The dark vortex also came to a halt in January and began moving northward again." "Perhaps shedding that fragment was enough to halt its progress towards the equator." The researchers are still analyzing more data to see if dark spot jr. lingers through the rest of 2020.

The massive vortex, which is larger than the Atlantic Ocean, was being pushed south by atmospheric forces near the equator toward certain doom when it abruptly reversed course and began drifting northward.

This visible-light image was captured by Hubble's Wide Field Camera 3 on Jan. 7, 2020, around the same time a slightly smaller dark spot mysteriously appeared nearby. After a few months, that location vanished. The smaller feature could have been a shard of the larger storm that shattered as it approached the equator.

In September 2018, Hubble discovered the massive storm in Neptune's northern hemisphere. The feature spans about 4,600 miles. The smaller spot's estimated width is 3,900 miles. The large storm is Hubble's fourth transient dark spot discovered since 1993. Two dark features in Neptune's southern hemisphere were first imaged by NASA's Voyager 2 spacecraft in 1989 as Voyager flew by the distant planet. By the time Hubble looked at Neptune in 1994, the storms had vanished. In 1994 and 1996, Hubble discovered two new dark spots in the planet's northern hemisphere.

It's not clear how these storms come to be. In comparison to surrounding regions in the gas giant's atmosphere, their clouds may be rising to higher altitudes. Neptune's predominant blue color is caused by the distant planet's methane-rich atmosphere absorbing red light.