Our Moon is unusually large for a small planet like Earth. Did it form from a single impact with a Mars-sized body, or did it form over time from multiple impacts?
Phobos Is Running Out Of Time
Phobos is so close to Mars that it orbits the planet three times a day. It’s also so close that the small moon is doomed.
Yin Yang Moon
Saturn’s moon Iapetus has a strange yin yang coloring, as well as a mysterious equatorial ridge.
Short Circuit
If you’ve ever experienced a thunderstorm, you’re well familiar with the ability of Earth to build a static charge on its surface. When that static build-up reconnects with a similar build-up in the sky, the resulting current is seen as lightning. We’ve long known that a similar static buildup can occur on other solar system bodies. We’ve observed lightning storms on Jupiter, Saturn and Venus, for example. Of course these planets all have thick atmospheres, so what about bodies without atmospheres?
Dance Magic Dance
Janus is a small moon of Saturn. It is somewhat oval in shape and has a diameter of about 180 kilometers. Epimetheus is another moon of Saturn, with a diameter of about 120 kilometers. The two moons are very similar, even down to their orbits. They share the same orbital plane, and at the moment the orbit of Janus is only about 50 kilometers closer to Saturn than that of Epimetheus. In other words the gap between the orbits is less than the size of the moons.
Looking for Lava in All the Wrong Places
In 1979 Linda Morabito was processing an image taken by the Voyager 1 spacecraft. It was an image of Io, one of Jupiter’s moons. She discovered what appeared to be a plume of material erupting from Io’s surface. Upon further analysis it was found to be due to a volcanic eruption, as was the first evidence of active volcanism on a body other than Earth. We now know that Io is the most geologically active body in our solar system.