The European Space Agency (ESA) has announced plans to build and send into orbit a satellite to measure the faint glow that plants give off as they photosynthesize. The new satellite will join a series of missions that already measure and study the biological systems that control our planet. Known as the Fluorescence Explorer – or FLEX – the spacecraft will be the eighth installment in the organization's Earth Explorer missions to be given the go-ahead by ESA member states.