We already know a lot about our solar system. It’s nearly 4.6 billion years old, andconsists of eight planets and five known dwarf planets, for starters.

But did you know that our solar system may have once been home to a long-lost ninth planet? Were you aware that, in the future, Mars could have Saturn-like rings? Those are just a few of the many exciting discoveries scientists made about our solar system this year. Scroll down for eight of our favorites.

1. There are blue skies and red ice on the dwarf planet Pluto.

Ever since NASA’s New Horizons spacecraft soared just 7,750 miles near Pluto in July — marking the closest ever approach to the dwarf planet — it has been beaming back to Earth new data and images of the distant world. So far, we’ve learned that the dwarf planet has blue skies and crimson-colored patches of water ice, includes craters and mountains on its surface, and houses ice-spewing volcanoes.

2. We learned a lot about the history and future of Mars.

Scientists have long known that Mars was once incredibly Earth-like and may have been home to massive lakes and streams. However, billions of years ago, solar wind likely stripped away the red planet’s atmosphere, leading to the disappearance of its water, NASA researchers revealed in a press conference in November.

And while Mars was similar to Earth in its past, it may look more like Saturn in its future. A new study suggests that planetary rings may develop around the red planet 20 million to 40 million years from now.

3. Our solar system has a missing planet.

That’s right. Our solar system may have been home to a mysterious world very similar to the four “giant” planets of Jupiter, Saturn, Uranus and Neptune some 4 billion years ago, researchers revealed in August.

Whatever happened to that planet? A study published in November suggests that a collision with Jupiter, the largest planet in our solar system, likely ejected the long-lost planet out of our solar system.

4. We spotted the most distant object in our solar system.

There may be a dwarf planet about half the size of Pluto lurking some 9.5 billion miles from the sun, making it the most distant object in the solar system discovered so far. Astronomers announced in November that they spotted what they believe to be the planetoid, dubbed V774104.

5. One of Saturn’s moons has a global, sprawling ocean.

Scientists had previously suspected that Saturn’s moon Enceladus had a body of water hidden under its icy crust, but in September NASA researchers revealed just how large that body of water may be. The researchers now believe that it expands across the entire moon.

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