Scientists Explore Mercury's Inner Core Through Its Gravity and Spin

Watching the way Mercury spins, NASA planetary scientists have succeeded in deducing its inner composition. The researchers from NASA's Goddard Space Flight Center in Greenbelt, Maryland have found evidence that Mercury's inner core is solid and nearly the same size as Earth's inner core. 

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"Mercury's interior is still active, due to the molten core that powers the planet's weak magnetic field, relative to Earth's," said Antonio Genova, an assistant professor at the Sapienza University of Rome who led the research while at NASA Goddard.

"Mercury's interior has cooled more rapidly than our planet's. Mercury may help us predict how Earth's magnetic field will change as the core cools."

To explore what the core of Mercury is made of the team used several observations from the MESSENGER (Mercury Surface, Space Environment, GEochemistry, and Ranging) mission looking at the planet's spin and gravity. The MESSENGER spacecraft spent four years observing Mercury.

Scientists were able to deduce that Mercury spins much more slowly than Earth. Its days last about 58 Earth days.

The researchers used tiny variations in the way Mercury spins to reveal clues about its internal structure. However, more data was needed to determine the planet's inner core. That is where gravity came in.

"Gravity is a powerful tool to look at the deep interior of a planet because it depends on the planet's density structure," said Sander Goossens, a Goddard researcher who worked with Genova on this study.

As MESSENGER got closer to Mercury's surface, scientists were able to extrapolate how the spacecraft accelerated under the influence of the planet's gravity. The researchers then put all that data into a sophisticated computer program.

The results detailed the interior composition of Mercury. The program showed that Mercury must have a large, solid inner core of about 1,260 miles (about 2,000 kilometers).

"We had to pull together information from many fields: geodesy, geochemistry, orbital mechanics and gravity to find out what Mercury's internal structure must be," said Goddard planetary scientist Erwan Mazarico, who also helped Genova reveal Mercury's solid core.

Now, the researchers are hoping to find even more discoveries about Mercury in MESSENGER's archives. "Every new bit of information about our solar system helps us understand the larger universe," said Genova.

The study is published in Geophysical Research Letters.