Planetary scientists at NASA found evidence that Mercury has a solid metal inner core that is similar in size to that of Earth's.

A team from the Goddard Space Flight Center in Maryland observed the rotation of the solar system's innermost planet and used the data from previous mission to study the interior of Mercury. They believe that the latest discovery can lead to a better understanding of how the solar system formed and how the rocky planets within evolved over time.

Mercury's solid inner core was described in the American Geophysical Union's journal Geophysical Research Letters.

What Lies Underneath The Surface Of Mercury

There has been two spacecraft that has visited and explored Mercury so far: the Mariner 10, which flew by the planet in the 70s and the Mercury Surface, Space Environment, GEochemistry, and Ranging or MESSENGER, which entered the planet's orbit in 2011. A third spacecraft, BepiColombo, was launched in 2018 and is expected to enter the orbit of Mercury in 2025.

MESSENGER spacecraft plunged into the surface of Mercury in 2015. However, before the end of its mission, it was able to gather crucial data about the spin and gravity of the planet that researchers used to study the interior of Mercury.

Scientists have been using observations of a planet's spin to determine its inner structure. In 2007, radar observations from Earth detected small shifts in the rotation of Mercury, which suggested that the smallest planet in the solar system has a liquid-molten metal outer core.

To probe whether Mercury has a solid inner core, the researchers analyzed MESSENGER's data of the planet's gravity.

"Gravity is a powerful tool to look at the deep interior of a planet because it depends on the planet's density structure," explained Sander Goossens, a researcher at Goddard.

The researchers entered the MESSENGER data into a computer program that allowed them to figure out the inner composition of Mercury to match the way it rotates. They found that for the planet to spin the way it does, which is much slower than Earth it must have a large solid inner core.

The researchers estimated that Mercury's solid innercore is about 1,260 miles wide. It makes up about half of the Mercury's entire core, which is 2,440 miles wide. For comparison, Earth's solid inner core is about 1,500 miles wide and takes up about a third of the planet's entire core.

Evolution Of Rocky Planets

The researchers explained that studying Mercury could aid scientists predict what the future of Earth would look like.

"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 in Rome who led the study. "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."

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