NASA: ‘New study shows Mercury is shrinking’

A new NASA-funded study appearing in the October edition of the journal Nature Geoscience has found previously undiscovered cliff-like landforms on Mercury – a discovery which appears to indicate that the planet, like Earth, is currently a tectonically active world.

Using images obtained by the Mercury Surface, Space Environment, Geochemistry and Ranging spacecraft (MESSENGER), Tom Watters of the National Air and Space Museum in Washington, DC, and his colleagues detected a series of features known as small thrust fault scarps.

These cliff-like landforms resemble stair steps, and are small enough that the researchers believe that they relatively young, geologically speaking. If true, this would indicate that Mercury is still contracting and that Earth is no longer the only planet in the solar system that is still tectonically active as experts have long assumed, the US space agency explained in a statement.

“The young age of the small scarps,” said Watters, who is a Smithsonian senior scientist at the Washington museum, “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.”

Mercury surface

Small graben, or narrow linear troughs, have been found associated with small fault scarps (lower white arrows) on Mercury, and on Earth’s moon. (Credit: NASA)

Findings suggest that the planet experiences ‘Mercury-quakes’

Large fault scarps originally discovered during Mariner 10’s flybys of Mercury in the mid-1970s (and later confirmed by MESSENGER) found that the planet was shrinking, the agency said. The scarps formed as the planet’s interior cooled and began to contract. This, in turn, caused the crust to break and thrust upwards along faults, producing cliffs, some of which were quite large.

During the final 18 months of the MESSENGER mission, however, the spacecraft was travelling at a lower altitude, capturing higher-resolution images which revealed the presence of small fault scarps which researchers believe had to have been very young; otherwise, they would most likely have been destroyed when Mercury’s surface was bombarded by comets and meteorites.

These features, which NASA said are comparable to the young lunar scarps that act as evidence that the moon is also shrinking, suggest that the solar system’s smallest world undergoes seismic activity similar to earthquakes – “Mercury-quakes,” if you will. They added that the discovery is consistent with the fact that it has a recently-detected several-billion-year-old magnetic field and with the slow cooling process that its still-hot outer core is currently undergoing.

“This is why we explore,” said Jim Green, NASA Planetary Science Director Jim Green at the agency’s Washington DC-based headquarters. “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.”

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Image credit: NASA

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