NASA Research Shows Moon, Earth Cores Similar

January 11, 2011—New research applied to old data suggests Earth and its moon have similar cores. According to NASA, the team’s findings suggest the moon possesses a solid, iron-rich inner core with a radius of nearly 150 miles and a fluid, primarily liquid-iron outer core with a radius of roughly 205 miles. Where it differs from Earth is a partially molten boundary layer around the core estimated to have a radius of nearly 300 miles. The research indicates the core contains a small percentage of light elements such as sulfur, echoing new seismology research on Earth that suggests the presence of light elements—such as sulfur and oxygen—in a layer around our own core. The researchers used extensive data gathered during the Apollo-era moon missions. The Apollo Passive Seismic Experiment consisted of four seismometers deployed between 1969 and 1972, which recorded continuous lunar seismic activity until late-1977. “We applied tried and true methodologies from terrestrial seismology to this legacy data set to present the first-ever direct detection of the moon’s core,” said Renee Weber, lead researcher and space scientist at NASA’s Marshall Space Flight Center. The team, whose findings are published in the online journal Science, also analyzed Apollo lunar seismograms using array processing, techniques that identify and distinguish signal sources of moonquakes and other seismic activity. The researchers identified how and where seismic waves passed through or were reflected by elements of the moon’s interior, signifying the composition and state of layer interfaces at varying depths. Future NASA missions will help gather more detailed data. The Gravity Recovery and Interior Laboratory, or GRAIL, is a NASA Discovery-class mission set to launch this year. The mission consists of twin spacecraft that will enter tandem orbits around the moon for several months to measure the gravity field in unprecedented detail. The mission also will answer longstanding questions about Earth’s moon and provide scientists a better understanding of the satellite from crust to core, revealing subsurface structures and its thermal history.

An artist’s rendering of the lunar core as identified in new findings by a NASA-led research team. Graphic credit: NASA/MSFC/Renee Weber A close-up view of the Passive Seismic Experiment, a component of the Apollo Lunar Surface Experiments Package, which was deployed on the Moon by the Apollo 14 astronauts during their first extravehicular activity. Photo credit: NASA/JSC

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