July 5, 2013
Mass Volcanic Activity Masks Mercury’s Early History
Brett Smith for redOrbit.com - Your Universe Online
Ever since NASA's Mariner 10 sent back the first images of Mercury, scientists have been fascinated by the planet's unusually smooth surface.
According to an analysis of images provided by NASA's Mercury-orbiting MESSENGER (MErcury Surface, Space ENvironment, GEochemistry, and Ranging), a period of heavy volcanic activity essentially gave the planet a makeover about 4 billion years ago, erasing the first 400 to 500 million years of its history.
"By comparing the measured craters to the number and spatial distribution of large impact basins on Mercury, we found that they started to accumulate at about the same time, suggesting that the resetting of Mercury's surface was global and likely due to volcanism," said Simone Marchi, a research fellow at the NASA Lunar Science Institute and lead author of a report on the analysis that was published in Nature.
In their analysis, the team determined the sizes and the amount of craters in Mercury's most heavily cratered regions using images taken during MESSENGER's first year in orbit. Using a model that was originally developed for the Moon and based on lunar rock samples, the team constructed a model of Mercury that linked its crater distribution to a timeline, as rock samples collected from the Apollo missions allowed scientists to make connections between the amount of craters on a surface and its age.
The team determined for every one crater formed on a lunar surface per year, an analogous surface on Mercury is marked with three new craters in the same amount of time. They also found the oldest terrains on Mercury were impacted by the so-called Late Heavy Bombardment (LHB), a time period of frequent asteroid and comet impacts as determined by analyzing the various craters on the Moon, Earth, Mars and Mercury.
"Meanwhile, the age of the youngest and broadest volcanic provinces visible on Mercury was determined to be about 3.6 billion to 3.8 billion years ago, just after the end of the Late Heavy Bombardment," Marchi said.
The analysis indicated the resurfacing of Mercury was due to volcanism, and according to report co-author Clark Chapman, "the impact of large projectiles hitting Mercury's thin solid crust during the LHB may have enhanced the observed global resurfacing."
The $446 million MESSENGER was launched in 2004 and has been orbiting Mercury since 2011. It took a circuitous journey through the inner solar system on its way to its destination, flying by Earth once, Venus twice, and Mercury three times.
During the three Mercury flybys, which took place in January 2008, October 2008 and September 2009, the craft mapped almost the entire planet in color, providing the first close-up images of the solar system's innermost planet in 30 years. MESSENGER was able to image many areas unseen by Mariner 10. It also analyzed the makeup of Mercury's surface, atmosphere and magnetosphere.
MESSENGER was constructed at the Johns Hopkins University Applied Physics Laboratory where it is still operated from today. The craft was built to withstand the extreme thermal energy that comes with approaching the Sun.