March 1 marked the start of Carruthers' 24-month primary science mission, with NASA using the L1-halo-orbit observatory to repeatedly map Earth's ultraviolet hydrogen glow.
From about 1.5 million kilometers away, its wide- and narrow-field imagers will track hourly changes in Lyman-alpha emission and help reconstruct the geocorona in three dimensions.
The mission targets a halo previously measured to at least 630,000 kilometers from Earth—about 100 Earth radii—meaning the Moon's orbit lies inside this extremely sparse outer atmosphere.
That hydrogen cloud is scientifically important less for astronauts than for physics and astronomy: it traces atmospheric escape, responds to solar activity and space weather, and adds foreground light that lunar telescopes must subtract.
Carruthers is named for George Carruthers, whose Apollo 16 ultraviolet camera captured the first far-UV view of Earth's geocorona from the Moon in 1972.