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Mercury's hidden mantle shows up in new maps

Elizabeth Howell, News Writer
Mar 16, 2015, 18:17 UTC

Sen—The naked eye can only tell us so much information about the object we are looking at. It is usually by using other forms of light, such as ultraviolet or infrared, that scientists can figure out more about an object's properties.

That is certainly the case at Mercury, which NASA's MESSENGER (MErcury Surface, Space ENvironment, GEochemistry, and Ranging) spacecraft has been orbiting since 2011. The spacecraft probed the surface in X-rays and gamma rays and found new information about Mercury's mantle, a layer between the planet's crust and outer core.

Scientists mapped magnesium, silicon and aluminium across Mercury for the first time and compared it to more poorly mapped elements on the surface. This caused some distinctive features to pop out.

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Maps of magnesium/silicon (left) and thermal neutron absorption (right) on Mercury's surface. Red represents high values and blue low ones. Image credit:  NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington

In one area, scientists found traces of what they suspect was an ancient impact crater in a region that is more than five million square kilometres (two million square miles) across. The magnesium spotted in this area was likely blasted from Mercury's mantle when the impactor smashed into the surface.

Signals of Mercury's mantle were also found using another technique, which was hitting the surface with low-energy neutral particles (called neutrons).

In the Caloris basin—the largest and best preserved impact crater on Mercury—scientists spotted an area with a different composition than other volcanic plains. This means that the magma from the volcano came from "a chemically distinct portion of Mercury's mantle," stated the Johns Hopkins Applied Physics Laboratory, one of the partners on the mission.

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Craters form a shape reminiscent of Mickey Mouse on Mercury. Image credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington

"Earlier MESSENGER data have shown that Mercury's surface was pervasively shaped by volcanic activity," stated Johns Hopkins' Patrick Peplowski, who led the second study. He added that the magma evidence from the new study shows that Mercury has a diverse mantle, in terms of composition.

MESSENGER is nearing the end of its mission and is expected to crash into the surface later this year when it runs out of fuel. The spacecraft was the first to orbit Mercury and provided scientists with a wealth of surprises, including discovering water ice in permanently shadowed craters and finding organics, considered the building blocks of life, on the surface.

The global magnesium/silicon/aluminium data was published in Earth and Planetary Science Letters and led by Shoshana Weider, a planetary geologist and visiting scientist at the Carnegie Institution of Washington. Peplowski's neutron study was published in Icarus.