A group of three satellites that are to study the Earth's magnetic field. Launched in November 2013, Swarm is an Earth Explorer Opportunity Mission of the European Space Agency (ESA). It is conducting the most extensive survey ever of the Earth's geomagnetic field, to aid scientific understanding of the Earth's interior and climate. The three satellites were released from a single launcher, with one of them flying at 530 km above the other two flying at 450 km. They are taking high-precision and high-resolution measurements of the magnetic field's strength, direction, and variation, along with navigation, accelerometer, and electric field measurements. In March 2017, Swarm led to the discovery of supersonic plasma jets high up in our atmosphere that can push temperatures up to almost 10 000˚ C. A year later, Swarm data solved the mystery behind a low-altitude purple atmospheric auroral streak, dubbed Steve, showing it to be a fast-moving stream of extremely hot atomic particles called a sub-auroral ion drift. While it is created through the same general process as a normal aurora, it travels along different magnetic field lines and therefore can appear at much lower latitudes.