Images from NASA's Lunar Reconnaissance Orbiter (LRO) revealed 14 lobe-shaped fault cliffs. Such cliffs or scarps are normally formed when the heated interior of the moon cools and contracts allowing the solid crust of the moon to 'fold'. These tectonic features of the moon are typically dozens of yards or meters in height and less than 10 kilometres in length. Yahoo News reports that with the LRO images, scientists may have identified that the pull of the Earth's gravity is possibly opening up faults in the moon's crust.
Since being in orbit in 2009, the LRO has detected over 3,200 of these fault cliffs. Scientists who have been analysing the six years of data provided by the spacecraft say that the orientations of the cliffs would tend to be random if the only cause of the fault scarp formation is the cooling of the moon's interior. The logic to this being that forces of contraction would have been of equal strengths in all directions.
However, much to the surprise of the researchers, the orientations of the fault scarps are anything but random. The pattern in the orientation in thousands of the faults suggests a different influencing factor in the scarp formation.
According to these researchers, that influence is the Earth's gravitational pull.
In a statement to Space.com, the study's lead author and Smithsonian Institution's National Air and Space Museum planetary scientist Thomas Watters said, "We know the close relationship between the Earth and the moon goes back to their origins, but what a surprise [it was] to find the Earth is still helping to shape the moon."
The study reveals that the Earth's tidal forces are not uniform throughout the surface of the moon so that many of these fault scarps' orientations reflect a pattern based on the strength of the effect of the Earth's tidal forces on the parts of the moon that are either closest to or farthest from Earth. Close to the moon's equator, at low and mid latitudes, the orientation is north to south. Close to the moon's pole, at high latitudes, the orientation becomes east to west.
A model that incorporates the effects of both tidal and contractional forces on lunar surface closely resembled the actual fault cliffs that were observed on the moon.
LRO project scientist John Keller of NASA's Goddard Space Flight Center in Greenbelt, Maryland related, "With LRO, we've been able to study the moon globally in detail not yet possible with any other body in the solar system beyond Earth, and the LRO data set enables us to tease out subtle but important processes that would otherwise remain hidden."
