Researchers using data from NASA's MESSENGER mission recently revealed two new maps of the surface of Mercury, showing new details about the planet's chemical composition.

These new maps even revealed chemical compositions for several large areas on the planet that we haven't been able to study before. This new information could teach us more about Mercury's ancient history.

The MESSENGER mission, which launched 10 years ago, is the first mission to study Mercury up close. It reached the planet's orbit in 2011, where it started collecting data from its spectrometers to determine the chemical compositions of Mercury's surface. So far, those instruments discovered concentrations of chlorine, potassium, magnesium, uranium, iron, sodium, calcium, silicon, aluminum, sulfur and thorium.

Scientists created maps of Mercury's surface composition from that data, but those low-resolution maps only showed one hemisphere of the planet. However, now, MESSENGER scientists have used a new approach at getting better maps, including maps of the entire planet, revealing new insights about Mercury's chemical makeup.

These scientists used a new technique called X-ray fluorescence, which uses the Sun's X-rays to study a planet's surface composition. They combined this new data with existing data and came up with maps that covered all of Mercury and provided additional detail about the hemisphere already studied.

Scientists discovered one particularly large area covering nearly 3 million square miles with high calcium/silicon, magnesium/silicon and sulfur/silicon. This area also has the lowest aluminum/silicon ratios on the planet, which suggests that an ancient impact affected this area, exposing the planet's mantle.

Thanks to data obtained from MESSENGER's X-Ray spectrometer (XRS), we also now have maps that display how Mercury's surface absorbs low-energy neutrons.

"From these maps we may infer the distribution of thermal-neutron-absorbing elements across the planet, including iron, chlorine and sodium," says Patrick Peplowski of The Johns Hopkins University Applied Physics Laboratory. "This information has been combined with other MESSENGER geochemical measurements, including the new XRS measurements, to identify and map four distinct geochemical terrains on Mercury."

These scientists also learned that Mercury's largest impact basin, the Caloris basin, has a composition different from other similar features on the planet, suggesting that volcanic activity happened there because Mercury's mantle partially melted.

"The crust we see on Mercury was largely formed more than three billion years ago," says Larry Nittler of Carnegie Institution For Science, Deputy Principal Investigator of the mission. "The remarkable chemical variability revealed by MESSENGER observations will provide critical constraints on future efforts to model and understand Mercury's bulk composition and the ancient geological processes that shaped the planet's mantle and crust."

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