As our telescopes peer farther and farther into the cosmos and our Voyager spacecraft edge closer and closer to the edge of our Solar System, still we find there is a lot to be discovered about celestial bodies much closer to home. NASA’s Gravity Recovery And Internal Laboratory (GRAIL) mission explores the closest of them all, our moon.
Using two dishwasher-sized satellites to measure minute changes in the moon’s gravity, NASA hopes to learn more about the internal structure of our moon and suss out finer details about the moon’s creation. The two satellites measure the precise distance between them as they pass over the moon. As the GRAIL probes detect minute changes in that distance, they record those differences as changes in the gravitational pull of the moon:
The gravity field map reveals an abundance of features never before seen in detail, such as tectonic structures, volcanic landforms, basin rings, crater central peaks and numerous simple, bowl-shaped craters. Data also show the moon’s gravity field is unlike that of any terrestrial planet in our solar system…
“What this map tells us is that more than any other celestial body we know of, the moon wears its gravity field on its sleeve,” said GRAIL Principal Investigator Maria Zuber of the Massachusetts Institute of Technology in Cambridge. “When we see a notable change in the gravity field, we can sync up this change with surface topography features such as craters, rilles or mountains.”
The data has been compiled into two fascinating videos of the topography of the moon. The first displays the thickness of the moon’s crust. This one conforms pretty closely to what you might have expected of the moon, just from staring at it. The craters and gullies we know are there show where our moon has been bombarded in the past:
The second video, showing the variance in gravitational pull, reveals a much more complex world than we’ve generally assumed to be up there. The channels and pock marks reveal much more tectonic and bombardment activity than is generally understood to be taking place on the moon:
It would be interesting to see this same type of data gathering applied to other rocky worlds beyond our own moon. For example, we know gravitational pull keeps Mercury pretty hot in its center, but how much pull is really being exerted and where? Other moons such as Callisto or Ganymede of Jupiter might be candidates for further study in this way, if it is even possible to get that type of equipment that far.