After a few weeks off for the holidays, the New Horizons team is back to releasing new weekly images of Pluto. Today's new images are two high-resolution stunners: one focuses on a potential ice volcano, while the other shows off Pluto's hazy blue atmosphere.
Wright Mons (pictured above), measures 90 miles (150 kilometers) across and 2.5 miles (4 kilometers) tall, and is one of the larger visible features of Pluto. Thanks to New Horizons, scientists now believe it’s an ice volcano. If that’s true, it’s the largest in the outer solar system — one that works basically the same way that volcanoes do on Earth, except with regards to what an ice volcano spews: ice, not magma. A high-resolution image of Wright Mons was included in one of the final image releases of 2015, but today’s new view offers the first detailed look with color information, too.
Ice volcanoes on Pluto get scientists excited because they overturn our existing knowledge of how the things form. Typically, ice volcanoes are found on cold moons like Triton or Enceladus. Since they orbit large planets (Neptune and Saturn, respectively), they are subject to tidal forces, which can heat a moon’s core enough to cause the icy ejections through weak spots in the moons’ surfaces. The material immediately refreezes and either settles on the surface or continues out into space. (Enceladus ejects so much of this material that it's the main supplier for one of Saturn's many rings.)
Ice volcanoes on Pluto would have to come from another source, because its largest moon, Charon, isn’t big enough to generate those tidal forces. One of the leading theories is that Pluto contains a core packed with still-radioactive material, which generates enough heat to influence surface features like these cryovolcanoes. But NASA is not ready to make a call on whether these are ice volcanoes, or where they come from. That's not surprising; after all, there is another nine to 10 months of new data left to analyze.
The image of Pluto's atmosphere is the highest-resolution color view released to date. Four different images from the Long Range Reconnaissance Imager (LORRI) were blended together to create the mosaic image, and team scientists used data from the Ralph/Multispectral Visible Imaging Camera (MVIC) to colorize the image. The resulting mosaic has a resolution of .6 miles (1 kilometer) per pixel.
We've known since shortly after the flyby that Pluto's atmosphere extends as far as 1,000 miles from the dwarf planet's surface. But closer inspection over the subsequent months has taught NASA much more. For instance, the agency believes that the blueish haze is a result of a process similar to the one that produces blue skies on Earth. On Pluto, sunlight hits and reacts with atmospheric molecules like methane, creating hydrocarbons like acetylene and ethylene. Those hydrocarbons scatter the sunlight, creating the blue haze.
NASA has published images of this haze before, but the distinction between the atmospheric layers is most visible in this image. It's also high resolution enough to even make out landforms on the surface; some of Pluto's mountains are visible in the bottom right.