The smallest planet in our solar system may be getting even smaller, according to a new global imaging and topographic data collected from a MESSENGER mission, The Los Angeles Times reported.
The findings, recently published online in Nature Geoscience, show that Mercury contracted radially by as much as 4.4 miles.The results are based on a global study of more than 5,900 geological landforms, such as curving cliff-like scarps and wrinkle ridges, that have resulted from the planet's contraction as Mercury cooled, according to a press release.
Mercury sits less than 36 million miles from the sun - less than two-fifths of the Earth-Sun distance. It's mostly made up of its heavy iron core, which has about a 1,255-mile radius and leaves a thin rind of just 261 miles for its crust and mantle. The innermost planet also hosts permanently shadowed regions inside craters that are among the coldest spots in solar system.
"Determining the extent to which Mercury contracted is key to understanding the planet's thermal, tectonic and volcanic history, and the structure of its unusually large metallic core," the study authors, led by Paul Byrne of the Carnegie Institution of Washington, wrote in the paper.
The new images show that Mercury has contracted far more than previous estimates. Prior to the MESSENGER mission, only about 45 percent of Mercury's surface had been imaged by a spacecraft. Old estimates suggested that the planet had contracted radially by about ½ to 2 miles substantially less than that indicated by models of the planet's thermal history.
"These new results resolved a decades-old paradox between thermal history models and estimates of Mercury's contraction," Byrne, a planetary geologist and MESSENGER visiting investigator at Carnegie's Department of Terrestrial Magnetism, said in a statement. "Now the history of heat production and loss and global contraction are consistent."
He added that the findings are also reminiscent of now-obsolete models for how large-scale geological deformation occurred on Earth when the scientific community thought that Earth only had one tectonic plate. Those models were developed to explain mountain building and tectonic activity in the nineteenth century, before plate tectonics theory.
