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NASA unveils first Mercury topography maps from MESSENGER craft

MESSENGER, the Mercury explorer, made 4,104 orbits around the planet closest to our sun. Originally sent for a one-year science sortie, MESSENGER far outlasted its planned expiry and stayed in orbit around Mercury, protected by its ceramic cloth sunshade. While it ran out of fuel and crash landed on the far side of the planet on April 30, 2015, NASA has spent the past year analyzing the data the probe returned. Now, the organization has unveiled stunning new topographic maps of Mercury’s surface — the first of their kind.

We sent MESSENGER (for MErcury Surface, Space ENvironment, GEochemistry, and Ranging) to characterize Mercury’s surface chemistry, geological history, and exosphere (quasi-atmosphere too rarefied to behave as a gas anymore), as well as finding out what’s actually going on with Mercury’s strangely paired core and magnetosphere. It represents a number of technological firsts, starting with being the first spacecraft to orbit Mercury. This is the first image of Mercury that MESSENGER sent, way back in 2011:

During a final extension of its already much-extended mission in March 2015, MESSENGER descended from its high, eccentric orbit to hover within a narrow band of altitudes from five to 35 kilometers from the planet’s surface.

This shallow orbit allowed MESSENGER’s surface team to execute seven “daring” orbit correction maneuvers, keeping the explorer aloft long enough for its laser to get a set of gorgeous topographic images amounting to a complete topo map of Mercury. The planet has about a 10km spread in its surface altitude. Its lowest point is some 5km below its average elevation, while its highest point is about 4km above average.

“MESSENGER had previously discovered that past volcanic activity buried this portion of the planet beneath extensive lavas, more than a mile deep in some areas and covering a vast area equivalent to approximately 60 percent of the continental United States,” said APL’s Nancy Chabot, the Instrument Scientist for the Mercury Dual Imaging System (MDIS). Mercury’s relatively young surface has been completely refreshed by the violence and frequency of its volcanic activity. Consequently, no part of its surface is quite as old as the planet itself, making the project of mapping Mercury’s topography an ongoing challenge.

The fact that MESSENGER spent most of its time close to Mercury around the planet’s high northerly latitudes mean that, just like on Earth, in its pictures the sun is always low in the sky. Long shadows can obscure the real color characteristics of the rocks. So MESSENGER’s MDIS captured images of the planet’s north pole using five narrow-band color filters.

The last whisper from the sturdy 1100-lb spacecraft was this image of the ground, the entire field of view already contained within the 93-km Jokai crater.

Even in its death, MESSENGER continues to provide a crucial source of data for the ESA’s BepiColombo spacecraft, which is supposed to get to orbit around Mercury in 2024. Because we know when and where MESSENGER made its crater, scientists now have a precise timepoint that they can use to measure the rate at which things like surface weathering and micrometeorites sculpt the planet’s craterous surface.

MESSENGER is something of a chemistry specialist, too. From its neutron spec and gamma spectroscopy data, we composited these images of Mercury’s surface chemistry: Rather than what we’d see with human eyes, the colors of these images represent different combinations of elements and geological ages.

That’s not the only notable thing MESSENGER reported about Mercury’s surface. There’s water ice on Mercury’s northern plains. There’s also dark, tarry-looking, probably organic sludge just laying on top of the ice. Together, they suggest that Mercury, too, may have been part of the cataclysmic rain of comets and other materials from the outer solar system that delivered water to the inner solar system and led to Earth’s carbon chemistry.

Read more about MESSENGER’s most notable discoveries and innovations from the Johns Hopkins Applied Physics Lab, the official home of the MESSENGER mission.

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