Saturn made news a few months ago when astronomers spotted what they believed was a new moon being born in the planet’s A Ring. As it turns out, the event was rare not because it featured the birth of a new moon, but because of its placement. Saturn’s F Ring, it’s outermost one, gives birth to moons fairly regularly, but those events are easy to miss because the moons die almost as quickly they appear.

To look at, the F Ring isn’t as bright as most of the inner ones, it’s made of chunky ice and is thinner than the others. But it does illustrate a principle called the Roche limit, which is the boundary beyond which moons can form and stay intact. Inside the Roche limit, gravity pulls at the newly formed moons on opposite sides with such force that it can tear them apart, particularly when they’re not particularly massive.

A few months after the donut-shaped Mars rock made its mysterious appearance (which we now know was thanks to being moved around by Opportunity Rover), scientists are pondering another great, and bigger, cosmic mystery — an object described as a “magic island” that suddenly appeared and then disappeared from one of Titan’s lakes.

NASA’s Cassini probe has been hanging out around Saturn’s largest moon for a while now, capturing image after remarkable image. Scientists examining those images found one that revealed a big object in the middle of one of Titan’s biggest bodies of water, Ligeia Mare, which is nearly 500 feet deep. Cassini snapped images of the sea in 2007, 2009, and 2013, and an image from July 10, 2013 shows a mysterious white blob, which scientists are calling the “magic island” until they know more. The island is approximately six miles wide and 12 miles long, and it doesn’t appear in images captured just two weeks later.

Some of you might have woken up on April 1 to find that Pluto had been reinstated as a planet. Of course, it wasn’t true — neither was the rumor that Richard Branson bought Pluto, thank the stars. But here’s some information about Pluto that appears to be totally legit: astronomers now think it has a subsurface ocean.

A new study proposes that, after a massive object smashed into Pluto, creating its moon Charon, the heat released by the collision warmed up a region in Pluto’s interior, creating an ocean that may still be there and may actually exist in liquid form. It seems crazy to think that a planet so far from the sun could have liquid water, but come on, it’s the Cosmos — strange and crazy are its bailiwick.

The Solar System’s most beautiful planet offers no end of discoveries, especially with Cassini on the job. But as dynamic as Saturn and its rings are, the planet’s moons are turning out to be the real revelation. Titan has oceans and probably moving waves, as well as salt flats, and is generally regarded as one of the best possibilities for harboring life in our neck of the woods. But focus has shifted to another of Saturn’s moons, Enceladus, which astronomers now think may be habitable due to the discovery of a hidden reservoir of liquid water under the surface.

Thanks to Cassini, scientists have known that Enceladus contains an ocean beneath its surface. Like with Jupiter’s moon Europa, the spacecraft captured images of water vapor coming from cracks in the southern pole. But the existence of plumes doesn’t necessarily mean the existence of liquid water. Scientists didn’t know if the vapor is a result of tectonic movement and friction. But now they know that there is indeed liquid water under the surface of the small, icy satellite.

If you watched Sunday’s episode of Cosmos, you know that Tyson and the Spaceship of the Imagination headed to Titan, Saturn’s gigantic moon that is thought to be one of the most likely spots for life beyond planet Earth in our solar system. As the ship cruised around, Tyson explained that the hydrocarbon lakes of Titan are the only bodies of surface liquid found outside of Earth. Just one day after that episode aired, scientists announced that they may have caught a glimpse of moving waves on the seas of Titan.

Of course, the hero in all this is the Cassini spacecraft, which continues to provide breathtaking and historical images of the solar system’s most picturesque planet. In 2012 and 2013, the spacecraft caught some reflective sunlight off the surface of a sea called Punga Mare, and scientists think it may have come from ripples — the kind only made on liquid. These aren’t big waves, we’re talking a few centimeters. But given that Punga Mare has always appeared to be completely flat, it’s still a major discovery.

When you realize that planets like Saturn have 60 moons, and Jupiter has 63, you have to wonder whether moons can have their own moons. Saturn’s satelite Titan is larger than the planet Mercury, so it’s not hard to imagine another rock circling it. Fraser Cain, publisher of Universe Today, one of my favorite space publications, tackled this question, and has dashed my hopes of discovering an infinite series of moons. It turns out that a moon can’t have a moon—unless some specific stuff is going on, which we’ll talk about later. At least the reasons this can’t happen are interesting, and that makes everything okay.

Apparently, “moon” has no explicit definition. If you look it up, you’ll find references to Earth’s Moon, but no official definition about what moons are in general. I thought science had this stuff nailed down. Moons do have some consistent attributes, though: they’re whole, sold objects that orbit around a bigger body, probably a planet, probably orbiting a star. Whatever the moon orbits is orbiting something else, etc. Technically, the Moon does have a moon, or at least something distinct orbiting it: NASA’s Lunar Reconnaissance Orbiter, which has been circling and photographing our Moon since 2009. But its lifespan is limited, and sheds light on why no moons in our Solar System can have their own satellites.