From the motions of the winds and tides, to the thickness of the polar ice sheets and the nature of Earth's magnetic field, ESA's Earth Explorers help us better understand the complex processes taking place on our home planet. Click for hi-res versionFollowing the successes of the ERS satellites and Envisat, which addressed Earth science issues of a global nature, Earth Explorers are smaller research missions dedicated to specific aspects of our Earth environment whilst demonstrating new technology in space. Earth Explorer missions focus on the atmosphere, biosphere, hydrosphere, cryosphere and Earth's interior with an overall emphasis on learning more about the interactions between these systems and the impact that human activity is having on Earth's natural processes.Designed for research purposes, Earth Explorer missions fall into two categories: 'Core' missions address specific areas of great scientific interest, and faster, lower-cost 'Opportunity' missions address areas of immediate environmental concern. GOCE, Aeolus and EarthCare are 'Core' missions, while SMOS, CryoSat and Swarm are 'Opportunity' missions.