If you had to describe a plant, the first thing you might start with is its colour – and the first colour that usually comes to mind, is green. And indeed, by and large, plants appear green to our eyes because they contain chlorophyll, which absorbs blue and red light much more strongly than green light. Behind this green façade though, plants are secretly glowing. This phenomenon is called solar induced fluorescence, and it gives scientists an unusual way to spy on photosynthesis – all the way from space.
As ESA prepares to launch its Fluorescence Explorer (FLEX) mission on 15 September 2026, here are 10 surprising facts about this faint glow that could transform how we assess the health of Earth’s vegetation.