Never-before-seen formations on Mercury's surface have been revealed in two new maps created with data from NASA's MESSENGER spacecraft that's been orbiting the planet since 2004.

MESSENGER is an acronym of MErcury Surface, Space ENvironment, GEochemistry and Ranging. This 485 kilogram robotic NASA probe is the first ever spacecraft to orbit Mercury and studies the planet's chemical composition, geology and magnetic field.

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The new maps show previously unidentified regions of Mercury. These regions or "geochemical terranes" have compositions significantly different from the crust surrounding them. Scientists said these zones provide insights into the formation of the outer surface of Mercury.

The maps also suggest the most recently identified features might have formed from the mantle and not from the planet's crust.

The maps were developed using MESSENGER's X-Ray Spectrometer (XRS) and Gamma-Ray Spectrometer (GRS) instruments that are being used to study the surface chemistry of Mercury.

Scientific analysis will reveal data about the concentrations of elements like potassium, uranium and sodium on the surface. The experiment will also give scientists the ratios of silicon to other elements on the planet's surface.

"The consistency of the new XRS and GRS maps provides a new dimension to our view of Mercury's surface," said lead author Shoshana Weider, of the Carnegie Institution of Washington.

"The terranes we observed had not been previously identified on the basis of spectral reflectance or geographical mapping."

The most visible of these unusual terranes is a large feature covering over five million square kilometers of the planet's surface. This terrane reveals the highest observed ratios of silicon to each of the elements of magnesium, sulfur and calcium. It also has some of the lowest aluminum-to-silicon ratios on the planet.

One possible explanation for the unusual region is that it stems from an impact that occurred long ago. The exposed mantle could have aided in the creation of the extremely large feature.

The second map using GRS shows the distribution across Mercury's northern hemisphere of elements that absorb thermal neutrons. Scientists were able to identify four distinct geochemical terranes by combining that information with previously obtained data.

"The crust we see on Mercury was largely formed more than 3 billion years ago," said Larry Nittler, deputy principle investigator of the mission and co-author on both studies.

"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."