The largest, shining object in Earth's starlit night sky, our Moon has long been the source of mystery, myth, and poetry--a captivating inspiration for those who stare at the sky in wonder. But Earth's Moon is a very real object--the only body beyond our own planet that we have actually set foot upon, leaving our lingering footprints in its distant, alien dust. Earth's Moon has been with us almost from the very beginning, and even though it is our planet's closest companion in space, it has nonetheless managed to keep some of its ancient secrets very well. In September 2015, astronomers released a new study that shed light on Earth's bewitching companion's ancient and secretive past. Although our Moon now appears to be unchanging, as if it has always been exactly the same as it appears now--going through its beautiful and, yet, familiar phases, and controlling our ocean tides--in the distant past, things were actually very different.
The three little moons (Methone, Pallene, and Anthe) orbit at very similar distances from Saturn, and they have a dynamical relationship. Mimas disturbs the trio of little moons, and causes the orbit of Methone to vary by as much as 20 kilometers (12.4 miles). Mimas causes the orbit of Pallene to vary by a slightly smaller amount--but it has the greatest influence on the orbit of the moon Anthe.
"We don't know how long the Dagwood-sandwich structure would exist. This structure represents a stable state, but various factors could mean the moon doesn't reach this stable state," Dr. Christophe Sotin said in a May 1, 2014 statement. Dr. Sotin is of the JPL.