Recent images from NASA’s MESSENGER spacecraft reveal small fault scarps on Mercury’s surface. These cliff-like landforms are small enough that planetary scientists believe they must be geologically young, which means the planet is still contracting and that Earth is not the only tectonically active planet in the Solar System, as previously thought.
This colorful view of Mercury was produced by using images from the color base map imaging campaign during MESSENGER’s primary mission. These colors are not what Mercury would look like to the human eye, but rather the colors enhance the chemical, mineralogical, and physical differences between the rocks that make up the planet’s surface. Image credit: NASA / Johns Hopkins University Applied Physics Laboratory / Carnegie Institution of Washington.
Large fault scarps on Mercury were first discovered in the flybys of NASA’s Mariner 10 in the mid-1970s and confirmed by MESSENGER, which found the planet was shrinking.
The large scarps were formed as Mercury’s interior cooled, causing the planet to contract and the crust to break and thrust upward along faults making cliffs up to hundreds of miles long and some more than a mile high.
In the last 18 months of the MESSENGER mission, the orbiter’s altitude was lowered, which allowed the surface of the planet to be seen at much higher resolution.
These low-altitude images revealed small fault scarps that are orders of magnitude smaller than the larger scarps, according to a team of researchers led by Dr. Tom Watters of the National Air and Space Museum.
“We report the discovery of small thrust fault scarps in images from the low-altitude campaign at the end of the MESSENGER mission that are orders of magnitude smaller than the large-scale lobate scarps,” Dr. Watters and co-authors explained.
“These small scarps have tens of meters of relief, are only kilometers in length and are comparable in scale to small young scarps on the Moon.”
“Their small-scale, pristine appearance, crosscutting of impact craters and association with small graben all indicate an age of less than 50 million years.”
“We propose that these scarps are the smallest members of a continuum in scale of thrust fault scarps on Mercury.”
Small graben, or narrow linear troughs, have been found associated with small fault scarps (lower white arrows) on Mercury, and on Earth’s moon. The small troughs, only tens of meters wide (inset box and upper white arrows), likely resulted from the bending of the crust as it was uplifted, and must be very young to survive continuous meteoroid bombardment. Image credit: NASA / Johns Hopkins University Applied Physics Laboratory / Carnegie Institution of Washington / Smithsonian Institution.
This active faulting is consistent with the recent finding that Mercury’s global magnetic field has existed for billions of years and with the slow cooling of Mercury’s still hot outer core.
“The young age of the small scarps means that Mercury joins Earth as a tectonically active planet, with new faults likely forming today as Mercury’s interior continues to cool and the planet contracts,” Dr. Watters said.
It’s likely that the planet also experiences Mercury-quakes — something that may one day be confirmed by seismometers.
“This is why we explore. For years, scientists believed that Mercury’s tectonic activity was in the distant past. It’s exciting to consider that this small planet – not much larger than Earth’s moon – is active even today,” said Dr. Jim Green, director of NASA’s Planetary Science division.
The team’s findings were published today online in the journal Nature Geoscience.
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T.R. Watters et al. 2016. Recent tectonic activity on Mercury revealed by small thrust fault scarps. Nature Geoscience 9 (10); doi: 10.1038/ngeo2814
This article is based on a press-release issued by NASA.
