[T]he $280 million mission aims to analyze a tenuous lunar atmosphere as well as to solve the mystery of the glowing horizon.
Horizon glow was detected by NASA's Surveyor landers in the mid- to late-1960s, as well as by astronauts during Apollo missions.
Surveyor landers recorded it as a thin band of light above the lunar surface along the moon's day-night line, or terminator. When Surveyor spotted the bands, they appeared to hover one or two meters above the surface, says Paul Spudis, a senior scientist at the Lunar and Planetary Institute in Houston.
Astronauts orbiting the moon, however, reported seeing streamers of light that extended hundreds of kilometers above the surface.
Light reflecting off of suspended lunar dust is the lead explanation for the phenomenon. But when the Clementine orbiter hunted for the glow during its time at the moon in 1994, it detected nothing.