When New Horizons set off to Pluto in 2006, we had almost no idea what we would find there.We knew a little about its size and composition, but that was mostly it. We didn't even really know what it looked like.

Then on July 15th 2014, New Horizons showed up at Pluto and totally blew our minds.

We found out the Pluto system is one of the coolest places we've ever explored, so to celebrate the fly-by's two year anniversary, here are some of the most exciting things that we've learned.

First, there's that giant super cute heart that scientists informally called 'Sputnik Planum'. That area is mostly made up of slowly flowing frozen Nitrogen. The mass of moving ice is one of the largest glaciers in the solar system!

But what's especially neat, is that the nitrogen ice is undergoing convection; the circular current that forms when the material heats up and cools down.

Pluto is pretty cold, at around -230 degrees Celsius on average. But the elements slowly decaying in Pluto's core create just enough heat to make underground Nitrogen ice all soft and mushy. Then that soft ice rises to the surface, cools down, and sinks down again! Kinda like a gigantic, groovy lava lamp.
A lot of scientists didn't expect to see active geology on Pluto, which made this discovery an awesome surprise.

New Horizon found that Pluto has plenty of mountains too, including some that are covered in methane ice.
And some of  of those mountains, like one called Wright Mons, even look like they could be cryovolcanoes, or ice volcanoes.
We didn't see anything actively erupting when New Horizons flew by, so we don't know for sure. But these volcanoes might erupt with a mixture of water ice, ammonia, methane or frozen Nitrogen, which is pretty neat for a little world so far away.

And the discoveries for Pluto weren't limited to the ground, or what could potentially erupt out of it. New Horizons also found that Pluto's sky is blue. Its just like home! That is besides the freezing temperatures, lack of sunlight, and toxic air...

Here on Earth the sky is blue because molecules like Nitrogen in the atmosphere scatter sunlight, but on Pluto molecules called Tholins do the scattering.
Tholins are complex organic molecules that form when UV light from the sun reacts with the Nitrogen and Methane from Plutos atmosphere.
The Tholins themselves are probably grey or red, and they help give Pluto's surface some of it's colour. But their small size helps make them perfect for scattering blue light.
Aah theres nothing like finding little reminders of home billions of kilometers away! 

While it was flying past Pluto, New Horizons also got our closest look at Pluto's moons; Charon, Hydra, Nix, Styx, and Kerberos.
And the largest moon Charon, had some fun surprises. For one thing, its North Pole, which the New Horizons team dubbed 'Mordor', is dark red, and Pluto might have had something to do with that.
In a paper published by the journal Nature last year, scientists suggested Charon's pole is red, because Pluto's atmosphere is staining it.

After methane escapes from Pluto's atmosphere, it's caught by Charon's gravity, and then collects and freezes on the moons north pole, one of the only places on Charon cold enough to have frozen methane all year. 
Then, ultraviolet rays from the sun cause a chemical reaction in the methane, which turns it into Tholins, those same reddish organic molecules that make Pluto's sky blue. We've never seen colour like Charon's before, and it looks like we can thank Pluto for that too.

But Charon can also take credit for some of its awesome features- like its gigantic canyon system that's 1800km long, and up to 7.5km deep!
Thats 4 times as long, and 4 times as deep as the Grand Canyon, even though Charon's diameter is less than 10% of Earth's.

The canyon probably stretches around most of Charon's surface, and there are also plenty of mountains on what we thought was going to be a boring, little moon.
Charon may of ended up with that uneven geology because of a sub-surface ocean, that froze a few hundred million years after the moon formed. 
Most of Charon's surface is made up of water ice, but astronomers think that right after Charon formed it might of been hot enough to melt some of the ice underground. Then over time, the underground ocean could have frozen, expanded, and created that huge fracture over Charon's surface.
We're not positive that that's exactly what happened, but the possibility of another ocean in the Solar System is just plain awesome.

So from the tip top of ice volcanoes to the bottom of super canyons, New Horizons has shown us that the Kuiper Blet is way more fascinating than we thought. And two years later, scientists still have plenty of data to analyze, so we'll be learning  alot more about Pluto and it's moons in the future.

Meanwhile, New Horizons is on track to visit another object in the Kuiper Belt, called 2014MU69, on New Year's Day, 2019. 

So this little space craft isn't done teaching us about the Solar System yet.

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