It was an incredible year for space exploration.
In 2015, we saw the world's first orbital rocket touch back down on the ground. We saw the beloved dwarf planet Pluto in exquisite detail. And an astronaut broke the record for the longest time spent in space.
We learned a lot about our own solar system this year, too, as NASA outlined in a recent blog post.
Here's a look at nine of the biggest discoveries we made in our celestial neighborhood in 2015.
We reached Pluto, and the world fell in love from 3 billion miles away. From mountains that rival the Rockies to frozen water on its surface, the tiny planet seems to have no shortage of surprises.
And for the first time, we landed a probe on a rubber ducky-shaped comet called 67P/Churyumov-Gerasimenko. Scientists discovered a shocking amount of oxygen, a surface covered in sinkholes, and more.
A spacecraft sampled a geyser spouting from a tiny moon called Enceladus and confirmed that it holds a vast subsurface ocean. Like Earth's oceans, it appears to have hydrothermal vents that may support life.
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