The View Improving, Less than One Pluto Day from Encounter
Pluto (right) and Charon (left) in a LORRI image, colorized with color information from the RALPH instrument onboard New Horizons. Courtesy NASA-JHUAPL-SWRI
Next week, we’ll be seeing some pretty sharp views of Pluto and Charon, but for my money, the view’s starting to get pretty good now! Here’s the latest image from July 8, when New Horizons was 6 million kilometers (3.7 million miles) from the pair and closing in fast. Now we can start to see more details, including what looks like surface features that could be impact craters. If so, and bear in mind that the craters aren’t yet proven to be craters, then the Geology, Geophysics, and Imaging team members will be looking at those holes in the Pluto surface to see what’s hidden below. One thing about impact craters, when they are created, their formation reveals the layers of ground (or other materials) below the surface. So, this will be an important discovery if New Horizons can “peek” down beneath the icy crust.
Personalities at the Frontier of the Solar System
What’s really cool about this image? It’s showing us Pluto has its own personality, just as Charon does, and they’re both worlds in their own rights. Pluto is covered with a mixture of nitrogen, carbon monoxide and methane ices, and their colors are made as solar ultraviolet radiation darkens the organic-rich ices. Charon is more uniformly darkish gray, with a mixture of water and ammonia compounds. How did they get this way? How have Pluto and Charon stayed together for billions of years? What else will we find?
These recent images show the discovery of significant surface details on Pluto’s largest moon, Charon. They were taken by the New Horizons Long Range Reconnaissance Imager (LORRI) on June 18, 2015. The image on the left is the original image, displayed at four times the native LORRI image size. After applying a technique that sharpens an image (called “deconvolution”), details become visible on Charon, including a distinct dark pole. Deconvolution can occasionally introduce “false” details, so the finest details in these pictures will need to be confirmed by images taken from closer range in the next few weeks. Credits: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute
As the New Horizons spacecraft gets closer to Pluto, we are seeing more detailed images of this world and its companion, Charon. The latest ones, taken with the LORRI instrument onboard the spacecraft, show what looks like a darkened pole on Charon, a somewhat lighter region below it, and some bright regions along the limb. “Fascinating” as Mr. Spock would say. But, what is happening at Charon to make it look like that? The final answer is a couple of weeks away, so let’s talk about how we figure out what’s happening at a world (planet, dwarf planet, moon, asteroid, or comet) from images of it.
An artist’s conception of Charon (with Pluto in the background). The plumes and brighter spots depicted on Charon’s “left side” are thought to be created as water (with some ammonia hydrate mixed in) “erupts” from deep beneath the surface. The material sprays out through cracks in the icy crust, immediately freezes and snows crystalline ice down onto the surface, creating a water-ammonia hydrate ice field. Such fields were detected and studied using the near-infrared imager on Gemini North. (This composite image includes Pluto and Charon models (enhanced), courtesy of Software Bisque. www.seeker3d.com, with plumes and ice fields added by Mark C. Petersen, Loch Ness Productions. Star field from DigitalSky 2, courtesy Sky-Skan, Inc.)
As in all other aspects of planetary science, you have to look for processes on the world you’re studying to understand how they affect the surface of that place. For example, if you were approaching Earth and were still quite a ways away as you came in to assume a standard orbit (Mr. Sulu), you’d likely notice the poles, the bluish color, and the darker areas that indicate land masses. The existence of ice at the poles tells you something about the climate and temperature in those regions. The bluish water in a liquid state tells you that conditions are good enough to permit liquid water. And, the land masses have many messages of their own, from the signatures of volcanoes to the ongoing (and long-term) deformation of the surface due to plate tectonics. What you see on Earth, even at the most cursory level — and at Pluto and Charon — are all caused by complex interactions comprising chemical reactions, atmospheric mixing, and actions going on below the surface.
So, with that in mind, what’s going on at Charon? I wish I could tell you for sure. But, it looks really, really interesting! Now that we’re seeing a great variety of surface features (or, as the scientists call it, “terrain types”) it’s a hint that Charon is not just a frozen dead world. A dark terrain could indicate some sort of chemical interaction as sunlight hits specific ices on the surface. That normally happens with methane-rich ice, which Charon doesn’t appear to have much (if any) of. Instead, it has been measured to be mostly water and nitrogen ice.
However, I suspect there’s more going on at Charon than meets the eye.
A few years ago, we created a graphic “approximation” of Charon for a project with Gemini Observatory. We had to guess at what the surface looked like. You can see that, even in 2007, we had an idea that there’d be darker areas on an already darkish object. The real interesting bit was that astronomers using Gemini telescope had spotted what looked like evidence for geyser-like activity on Charon. I will be really interested to see if New Horizons finds that same evidence and confirms such activity. If it does, then we’re looking at a dynamic world with an interior that is forcing mixtures of ammonia hydrates (ammonia mixed with water) and water crystals onto the surface. And, THAT’s cool.
I don’t know why Charon has a dark pole, yet. I suspect that the New Horizons mission team members don’t YET know for sure. They’re likely going through all the ideas en masse, and once they have more data, we’ll all know what’s ticking inside this little world.
