Neptune’s storm dodges its demise
A change of direction stopped the storm from straying to the planet’s calm equator
It continues to be a dark and stormy time on Neptune, as a 7,400km-wide storm has saved itself from destruction, it was recently revealed. And it may have created a smaller companion in the process.
The Hubble Space Telescope has been watching the dark spot created by the storm move south towards the planet’s equator since it was discovered in 2018. Such storms are thought to be kept stable at mid-latitudes by the Coriolis force, which is created by the planet’s spin. As this force is weaker at the equator, storms tend to blow themselves out when they drift into the region, so the observing team were expecting to watch the dark patch disappear.
Instead, in August 2020 the team noticed the storm had taken an abrupt turn northwards, sparing itself this untimely demise. No one has seen this kind of storm behaviour in the outer planets before.
“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 H Wong from the University of California at Berkeley, who took part in the study. “That was surprising.”
Even more surprisingly, Wong and his fellow astronomers also noticed that a second, smaller transient dark spot had appeared near the storm’s equator-facing side, which they nicknamed ‘Dark Spot Jr’.
"When I first saw the small spot, I thought the bigger one was being disrupted,” said Wong. “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.”
Although Hubble has seen many storms in the atmosphere of Neptune in the last 30 years, this one has been the most closely studied, as it’s been watched as part of the Outer Planet Atmospheres Legacy (OPAL) programme. This initiative takes regular images of the four outer planets with Hubble, creating an archive of images tracking the planets through the years. Astronomers can then use this archive to see how the planetary atmospheres change over time. https://archive.stsci.edu/prepds/opal