For those who believed that the Moon was just a rock spinning aimlessly or a “dead” place, there is now a study that has just broken the idea that the Moon is an inhospitable site that only moved when a meteorite hit, because the Moon also trembles. And it has been doing so for millions of years. Right beneath one of the most iconic places in space exploration, the Taurus-Littrow Valley, where Apollo 17 landed in 1972.
The study reveals that there have been landslides in the terrain and that they were not caused by space impacts, but by shallow lunar quakes. And of course, this must be taken into account if we want to build on the Moon.
What happened?
It all begins on the very ground that the last astronauts of the Apollo program walked on. At the time, those giant fallen rocks and regolith slides were explained almost automatically as being caused by meteorites. That was the logical explanation in a world believed to be geologically inactive.
But now, decades later, scientists have taken another look at those samples collected by the astronauts, using much more modern tools, and they have been able to calculate how long those rocks had been exposed on the lunar surface.
And what did they find?
They discovered that it was not a one time event, but a pattern, different tremors that occurred again and again over tens of millions of years. The valley where Apollo 17 landed was, for a very long time, a seismically active area.
The Lee-Lincoln fault
This is the name of a visible fracture that runs through the valley. According to the analysis, this fault has been generating quakes with magnitudes close to 3. On Earth, that would be minor, a light tremor. But on the Moon, with a rigid and highly fractured crust, the effect can be much more serious, especially if it occurs near the surface. It is not so much the strength of the quake that is concerning, but its repetition.
And what do those moonquakes look like?
Since the Moon does not have an active seismic network like Earth, researchers had to look for other clues, and they found them in the rocks.
Moving a rock weighing several tons is not easy. It requires a minimum ground acceleration, and by calculating that force and comparing it with models of how seismic waves propagate on the Moon, scientists were able to reconstruct what kind of tremors must have occurred. Large nearby impacts are not needed to explain everything, because internal quakes fit perfectly with what is seen on the ground. And that is how they managed to “read” the earthquakes that have occurred on the Moon over all these centuries.
Were the Apollo 17 astronauts in danger?
This is the question that comes to many people’s minds. And the answer, fortunately, is quite reassuring. The probability that a dangerous quake would occur during the few days the mission lasted was very low. In the worst case scenario, the most that could have happened was that the lunar module might have lost stability on the ground.
And for those who return to the Moon?
Of course, when humans return to the Moon, they will have to be careful about where they step. Building near geologically young faults means assuming an unnecessary risk, and architecture will also have to be reconsidered, because tall structures can be much more vulnerable.
Lunar quakes
For those who believed the Moon was just an inert rock, it has history, dynamics, and now even its own risks.