Earth's Moon Reveals An Ancient Secret. Many astronomers think that during an ancient era, termed the Late Heavy Bombardment, our young Moon was violently battered by a marauding multitude of invading asteroids that crashed onto its newly formed surface. This attack of pelting objects from space occurred about 4 billion years ago, and the shower of crashing asteroids excavated impact craters, and also slashed open deep fissures, in the lunar crust. This sustained shower of merciless impacts increased lunar porosity, and opened up an intertwining network of large seams under the Moon's surface.
The original goal of Cassini-Huygens was to study Saturn and its large, misty, tortured, moon Titan. Titan, the second-largest moon in our Solar System, after Ganymede of Jupiter, is a world long-shrouded in mystery, hiding behind a thick orange veil, and slashed with hydrocarbon lakes and seas. However, there are other enticing moons known to circle the ringed planet. Saturn's mid-sized icy moons (Mimas, Enceladus, Tethys, Dione, Rhea, Hyperion, Iapetus, and Phoebe) are enchanting worlds. Each one of these frozen little moons reveals an interesting and unique geology. So far, Saturn is known to sport 62 icy moons!
Some astronomers think that the two gas-giants do not sport solid surfaces secreted beneath their immense and heavy gaseous atmospheres, although others suggest that the jumbo-size duo do, indeed, harbor relatively small cores of rocky-icy stuff. The two other large inhabitants of the outer limits of our Sun's family are Uranus and Neptune, which are both classified as ice-giants, because they harbor large icy cores secreted deep down beneath their heavy, dense gaseous atmospheres which, though very massive, are not nearly as heavy as the gaseous envelopes possessed by Jupiter and Saturn.