Mercury probe's flyby gives long awaited answers to planet's composition

by Rich Bowden - Jul 3 2008, 20:45

NASA's Mercury Surface, Space Environment, Geochemistry and Ranging (MESSENGER) spacecraft's close flyby of the closest planet to the sun in January has yielded important evidence of vulcanism in the planet's formation, settling a long-standing scientific disagreement.

In a series a papers written in the July 4 issue of Science magazine scientists explained how the space probe made its first flyby of Mercury on January 14 to within a distance of about 124 miles (200 kilometres) over the planet's surface. The probe was able to give scientists views of the planet never seen before and in the process solving a 30-year-old mystery surrounding the planet's composition.

MESSENGER's higher resolution pictures and broader sweep was able to confirm that volcanic activity had been involved in the formation of the planet's plains, settling a question first posed by the Mariner spacecraft in 1975. The early images provided by Mariner split scientific opinion between those that said the regions came from material that was ejected by large impacts and then formed smooth "ponds," and those that believed the plains material derived from erupted lavas.

MESSENGER science team member James Head said the probe better pictures and angle of the sun on the planet's surface revealed the features were "distinctly different from [their] surroundings," adding that the pictures show evidence of smaller craters being completely erased, "clear evidence that you're looking at lava flows."

The flyby also studied the chemical composition of Mercury's surface, analysed its atmosphere and observed that its core makes up around sixty percent of the mass, more than as much as other terrestrial planets.

Remarking on the importance of the core to surface geological structures, Principal Investigator Sean Solomon at the Carnegie Institution of Washington said, "The dominant tectonic landforms on Mercury, including areas imaged for the first time by MESSENGER, are features called lobate scarps, huge cliffs that mark the tops of crustal faults that formed during the contraction of the surrounding area."

"They tell us how important the cooling core has been to the evolution of the surface. After the end of the period of heavy bombardment, cooling of the planet's core not only fuelled the magnetic dynamo, it also led to contraction of the entire planet. And the data from the flyby indicate that the total contraction is a least one-third greater than we previously thought," he stated.

Image: Mercury. Credit: NASA/APL

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