Nasa has discovered “surprise” X and C shapes in the Earth’s atmosphere - and scientists are struggling to explain them. While these alphabetical shapes have been observed before, Nasa’s Global-scale Observations of the Limb and Disk (GOLD) mission sees them more clearly than other instruments have and is now finding them where and when scientists didn’t expect. These unexpected appearances tell scientists that something else must be involved in forming these X shapes. Computer models suggest that the X could develop when changes in the lower atmosphere pull plasma downward. “The X is odd because it implies that there are far more localized driving factors,” said Jeffrey Klenzing, a scientist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, who studies the ionosphere.