A storm nearly the size of the Earth has suddenly appeared on Neptune, in a region where large cloud formations have never been spotted before. Normally bright clouds on Neptune are seen in the latitudes closer to the poles, not near the equator. The storm was spotted by astronomers at WM Keck Observatory during a test run. The storm system is 9,000 km in length, almost a third of Neptune's radius. The storm is unusually bright, and grew brighter between 26 June and 2 July.
Ned Molter, a student from the University of California, Berkeley who spotted the storm system says, "Seeing a storm this bright at such a low latitude is extremely surprising. Normally, this area is really quiet and we only see bright clouds in the mid-latitude bands, so to have such an enormous cloud sitting right at the equator is spectacular." The clouds are expected to be made of methane, and are believed to be forming because of a large high pressure system deep within the Neptunian atmosphere.
Neptune is one of the windiest planets in the solar system, with winds at the equator reaching 1,609 km/h, while a category 5 hurricane on Earth has speeds approaching 240 km/h. The speeds of wind on Neptune varies with latitude, just as it does on other planets. At such speeds it is very difficult to explain phenomena that can hold such a large system together. If it is not a vortex deep within the atmosphere, the other possible explanation is that the storm is made up of a large convective cloud.