Scarps are a well known feature on Mercury's surface, some of which are known to create steep cliffs extending hundreds of miles long and, in some places, reach over a mile high. These geological features were first documented by the flybys of NASA's Mariner 10 spacecraft in the 1970's and later confirmed by MESSENGER. These observations helped planetary scientists reveal that, as the planet cooled over hundreds of millions of years, the entire mass contracted, creating these scarps as the surface buckled under the pressure.
But as MESSENGER made its final orbits around Mercury, it noticed far smaller scarp-like features. If these small scarps were ancient, they should have been eroded away long ago by the continuous erosion of meteoroids and comets, which led Watters and his team to realize these were young features. So, far from being a static world Mercury could be a hothouse of "Mercury-quakes" as the entire planet contracts, further crushing its crust today.
RELATED: Forever Farewell: NASA's Mercury Probe Is Now an Impact Crater
Interestingly, Mercury's scarps are of a similar scale to our moon's scarps, a celestial body that is also currently shrinking.
"This is why we explore," said NASA Planetary Science Director Jim Green at NASA Headquarters in Washington, D.C. "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."