GEOTAIL was launched jointly by Japan and the United States in 1992 and spent more than 30 years observing electromagnetic waves and plasma in Earth's magnetotail.
GEOTAIL's observations built a long-term reference data set on chorus generation, spatial distribution, and frequency behavior.
GEOTAIL's vantage point in the distant magnetotail, roughly ten Earth radii from Earth, provides conditions that resemble the compact magnetosphere of Mercury.