Chasms, craters and a dark north polar region are revealed in this image of Pluto’s largest moon, Charon, taken by the New Horizons spacecraft. (NASA/JHUAPL/SWRI)

On Tuesday, NASA's New Horizons spacecraft will make its closest pass of Pluto, the dwarf planet never before visited by humankind. As the spacecraft gets closer and closer to the target of its long-awaited flyby, our images of Pluto and its moons get better and better. On Sunday, NASA released new images of Charon, Pluto's largest moon and a world that may be even more interesting than Pluto itself.

[Graphic: 9 years and 3,000,000,000 miles to Pluto]

Here's a bit about Charon from an earlier post on the blog:

The two form an odd pair: Charon is half the size of Pluto at 750 miles across, making it the largest known moon relative to its host planet. And instead of following the traditional courtship of a moon orbiting around its host, Pluto and Charon orbit in sync around a fixed point between them.

They act more like a binary planetary system, with Pluto's smaller moons struggling to stay stable around the pair's strange cosmic dance. But their compositions seem to be radically different, and pinning down what they're made of could help scientists understand how they formed -- and why they act so strangely.

Indeed, Charon's moon status doesn't make it less important than Pluto: Scientists are interested in Kuiper Belt objects (such as Pluto and Charon) because they were formed at the very beginning of the solar system and have been kept extremely cold for the 4.6 billion years since. Chances are good that many of these objects contain pristine samples of the materials available when our solar system first formed. But Pluto -- being a planet and all -- has been pretty active since those days. So it won't have kept those materials quite as pristine as its buddy Charon has.

[Why the July 14 Pluto flyby will be a spectacular event for all of us]

And Charon's craters will be a more direct record of ancient impacts than those on Pluto -- because geological processes on the dwarf planet will have reshaped its surface over the past few billion years. Scientists think the Kuiper Belt once had 100 times as many objects as it does now (which is impressive, as they estimate that it's currently full of a trillion comets) and by counting the impact craters on Charon they can confirm how highly trafficked the area used to be.

The latest image of Charon doesn't disappoint: Plenty of craters are visible already.


(NASA/JHUAPL/SWRI)

The largest chasm looks to be miles longer and deeper than the Grand Canyon. The largest crater is 60 miles across, and seems to have a floor darker than the surface surrounding it. This could mean that the ice exposed by the impact is of a different composition than the ice at the surface. A dark polar region spans 200 miles across, but we'll have to get a closer look to know what makes it different from the rest of the moon.

[This is the last picture we’ll see of Pluto’s mystery spots for a long time]

“This is the first clear evidence of faulting and surface disruption on Charon,” William McKinnon, deputy lead scientist with New Horizon’s Geology and Geophysics investigation team, said in a statement. “New Horizons has transformed our view of this distant moon from a nearly featureless ball of ice to a world displaying all kinds of geologic activity.”

Read More:

Why did NASA spend 9 years getting to Pluto only to fly right past it?

The inside story of New Horizons’ ‘Apollo 13’ moment on its way to Pluto

Why the U.S. Postal Service is excited about NASA’s mission to Pluto

Now Pluto has a heart on it

Why the July 14 Pluto flyby will be a spectacular event for all of us