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.
Titan Fall
Titan is the largest moon of Saturn, and the second largest moon in our solar system. It has a greater diameter than Mercury. It is also the only moon with a thick atmosphere. It has liquid methane rivers and lakes, and has a seasonal climate.
And like our moon, we have landed a probe on its surface. In 2005 the Huygens probe made a one-way journey to the surface of Titan. You can see a video of that landing above.
Wave the Titanic
Saturn’s largest moon Titan is in some ways very similar to Earth. Sure, it is significantly colder, and has a much thicker atmosphere, but it has something no other world besides Earth. Lakes and seas. These are not water lakes, but methane. With a surface temperature of about 94 K, and a thick atmosphere, Titan is perfect for a methane …
Splat
The mass of the Moon is about 1% that of Earth. That might seem pretty small, but it’s actually surprisingly large. The moons of other planets are tiny when compared to their planet’s mass. Just how Earth got such a large moon has been a bit of a mystery, but it has generally come down to two models: co-formation and collision.
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.
That’s No Moon
Cruithne is a small, rocky body about 5 kilometers across. It was discovered in 1986, and it is sometimes referred to as Earth’s second moon. The argument for calling it a moon of Earth is because it is gravitationally bound by the Earth, just like the Moon. But Cruithne doesn’t orbit the Earth, so what exactly is going on? The answer has to do with some interesting complexities of orbital dynamics.
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