There are weak, infrequent quakes, some triggered by tidal forces. Fossil magnetism was found in lunar rocks, although the Moon has no magnetic field. The source of the fossil magnetism is still unexplained. A large magnetic anomaly was found on the lunar farside, near the crater Van de Graff. There is some outgassing underway from the lunar interior, as shown by the detection of radon from lunar orbit.
Tiny crystals line a crack in a lunar rock.
Discoveries Tiny microcrater, made when a particle of cosmic dust struck a small bead of lunar glass on the Moon's surface. Rocks have remained exposed on the lunar surface for periods as long as 500 million years without being destroyed. Lunar soil analyses show that major variations in the amount and isotopic composition of solar wind nitrogen have occurred during the past 2.5 billion years. There do not appear to have been major changes in the intensity of solar flares and the composition of particles erupted from them over the past 100,000 years. The flux of galactic cosmic rays has apparently been constant on the Moon over the past 1 billion years.