NASA and the German Space Agency at DLR (German Aerospace Center) have agreed to jointly build, launch, and operate a pair of spacecraft that will yield insights into how Earth's water, ice, and land masses are shifting by measuring monthly changes in the planet's gravity field. Tracking large-scale mass changes—showing when and where water moves within and between the atmosphere, oceans, underground aquifers, and ice sheets—provides a view into Earth's water cycle, including changes in response to drivers like climate change.