March 17, 2014

New Data Suggests Mercury Contracted Far More Than Previously Thought

redOrbit Staff & Wire Reports - Your Universe Online

NASA’s MESSENGER spacecraft has uncovered evidence that Mercury has contracted far more than previously believed over the past four billion years, according to research appearing in Sunday’s edition of the journal Nature Geoscience.

In fact, lead author and Carnegie Institution of Washington planetary geologist Paul K. Byrne and colleagues analyzed global imaging and topographic data from the US space agency-sponsored mission and found that Mercury, the planet closest to the sun, has shrunk by as much as seven kilometers in radius over that time – far exceeding earlier estimates.

Byrne and his colleagues studied nearly 6,000 geological landforms, including curving cliff-like regions and wrinkle ridges, that resulted from contraction as the planet closest to the sun began to cool. In addition, their findings will provide new insight into Mercury’s thermal, tectonic and volcanic history, as well as the structure of its massive metallic core, the Carnegie Institution explained in a statement this weekend.

Mercury, which unlike Earth has just one tectonic plate, had only had approximately 45-percent of its surface area imaged by a spacecraft prior to the MESSENGER mission. Based on that limited coverage, scientists devised estimates which suggested that the planet had only contracted radially by between 0.8 and 3.0 km – far less than the 5.0 to 10 km suggested by models of the planet’s thermal history.

The new models, which are the first to be based upon a comprehensive survey of Mercury’s surface, indicate that the planet actually contracted radially by between 4.6 and 7.0 km – a substantial increase over the previous estimates that is more in line with the thermal model’s suggestion of how it achieved its modern radius of 2,440 km.

“These new results resolved a decades-old paradox between thermal history models and estimates of Mercury's contraction,” said Byrne, who is also a MESSENGER visiting investigator at Carnegie's Department of Terrestrial Magnetism. “Now the history of heat production and loss and global contraction are consistent.”

“Interestingly, our findings are also reminiscent of now-obsolete models for how large-scale geological deformation occurred on Earth when the scientific community thought that the Earth only had one tectonic plate,” he added. “Those models were developed to explain mountain building and tectonic activity in the nineteenth century, before plate tectonics theory.”

Among the tectonic faults studied by the researchers were lobate scarps (cliffs that form when thrust faults break the surface and reach upwards of two miles high) and wrinkle ridges (which are caused by faults that do not extend as deep and typically have lower relief, leading to a formation of a ridge when surface materials from one side of the fault fold over the other). A total of 5,934 such features were mapped by the scientists.

According to Sean Solomon, principal investigator of the mission and the director of the Lamont-Doherty Earth Observatory at Columbia University, "This discrepancy between theory and observation, a major puzzle for four decades, has finally been resolved. It is wonderfully affirming to see that our theoretical understanding is at last matched by geological evidence."

In addition to Byrne and Solomon, authors of the study include Christian Klimczak of the Carnegie Institution, A. M. Celâl Şengör of the Eurasia Institute of Earth Sciences, Thomas Watters of the National Air and Space Museum’s Center for Earth and Planetary Studies, and Steven Hauk II of Case Western University.

Image 2 (below): This image shows a long collection of ridges and scarps on the planet Mercury called a fold-and-thrust belt. The belt stretches over 336 miles (540 kilometers). The colors correspond to elevation -- yellow-green is high and blue is low. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington