Mercury – the planet closest to the sun – is far from a static chunk of rock. It’s tectonically active today, according to observations by the MESSENGER mission before it fell to its doom.
Thomas Watters from the Smithsonian Institute in Washington and US colleagues saw steep cliffs called scarps less than 10 kilometres long along fault lines in images snapped as the spacecraft zoomed into low-altitude orbit during the mission’s final leg.
These scarps were pegged at less than 50 million years old, suggesting that the planet is tectonically active today and despite its proximity to the sun, is slowly cooling.
The work was published in Nature Geoscience.
Before NASA’s MESSENGER probe plunged to its demise in April last year, it snapped nearly 300,000 images of Mercury’s surface during its four-year stint with the planet.
Most of these images were taken from high altitudes, showing vast volcanic plains, impact craters and ancient fault lines marked by giant eroded scarps stretching hundreds of kilometres.
But during its final 18 months, the craft dropped altitude to under 200 kilometres to get a closer look at the surface.
There, it was able to see to 200-metre resolution and found smaller scarps of less than 10 kilometres.
Unlike their bigger counterparts, these scarps were in pristine condition with crisp, defined clifftops that hadn’t yet eroded.
Some even crossed impact craters.
These suggested they were quite young (on a geological timescale, that is).
Using the rate of erosion on Mercury, Watters and his crew write that these small scarps were probably younger than 50 million years, “raising the possibility that some of the faults are active at present”.
These “Mercuryquakes” are likely triggered as the planet’s interior cools and contracts.
If a future Mercury mission includes a seismometer, it would likely able to measure quakes as the faults slip.