In 1989 the NASA spacecraft Voyager 2 streaked past Neptune on its way out of the solar system becoming the first spacecraft to visit the giant blue planet. Voyager 2 snapped pics of a couple of massive storms with the Earth-sized larger storm dubbed “The Great Dark Spot” and the smaller storm called “Dark Spot 2.”
Half a decade later the Hubble space telescope took some images of Neptune and scientists wanted to see the progress of the massive storms on Neptune. They were surprised to see hat the two giant storms had disappeared. Scientists found the disappearance of the storms to be a surprise because similar storms on Jupiter have lasted for more than a hundred years.
Scientists ran computer simulations of Neptune to try and gain understanding into the disappearance of the Great Dark Spot. Years later scientists are starting to understand why the storms disappeared thanks to the OPAL (Outer Planet Atmospheres Legacy) project. The team has been able to develop constraints that pinpoint frequency and duration of storm systems on the planet and witness a storm’s formation for the first time. That observation happened in 2015 with the development of a small dark spot in the southern hemisphere of the planet. The team monitored that storm as it dissipated.
Another dark spot emerged in 2018. The team said they were busy monitoring the smaller storm they didn’t expect to see a larger one so soon. The team had images of that second storm from its birth to its demise and found that white clouds formed in the region where the most recent dark spot would later appear. Data suggests that storms originate much deeper in the planet’s atmosphere than previously thought. The team says that some storms can last up to six years, but the average lifespan is two years. New storms are expected every four to six years.