2015 is full of epic stories and images from the final frontier. But one of the most stunning visits has to be New Horizons’ close encounter with Pluto in July. We’ve seen the breathtaking images. We’ve seen the videos made sweeping across high-resolution pictures. But what about a ‘real movie?’
Alex Parker, a research scientist working on NASA’s New Horizons mission, gives us a beautiful, colorful movie titled Pluto Through Stained Glass: A Movie from the Edge of the Solar System.
What’s with the stained glass appearance? The video was recorded by the LEISA instrument aboard the New Horizons spacecraft. It’s an infrared imaging spectrometer. It snaps 2-D images like a regular camera, but the similarities stop there. What makes LEISA special is its linear filter.
“One side of the camera can only see light of one specific wavelength of infrared light (light that has longer wavelengths than can be seen by our eyes), and each row of pixels can see a subtly different wavelength.”
This linear filter sees light from wavelengths as short as 1.25 microns to as long as 2.5 microns. How does that compare to us? We see wavelengths as short as 0.39 microns to as long as 0.7 microns according to Parker.
This range was chosen because many of the ices and other materials scientists expected to find on Pluto would easily be visible.
And it works perfectly. In October, NASA announced the New Horizons team found exposed areas of water ice on Pluto.
See the blue areas? Those are where the strongest ice spectral signatures are seen. The window in the lower left shows the LEISA spectra in two areas. The white line shows a water ice model spectrum, which the cyan line follows. The magenta line shows areas where methane ice absorption is seen.
The lower right window shows an enhanced color view of the region with the best water ice spectral signature. You can see how the area with the strongest water ice signature is a lighter shade of red. “I’m surprised that this water ice is so red,” said Silvia Protopapa, a member of the New Horizons science team. “We don’t yet understand the relationship between water ice and the reddish tholin colorants on Pluto’s surface.”
LEISA and Charon
LEISA is also telling scientists a lot about Pluto’s largest moon, Charon. Remember, LEISA wavelength spectrum isn’t just for water ice. One of Charon’s craters, informally named Organa, caught the eye of New Horizons scientists.
Structurally, Organa looks just like the rest of the craters peppering Charon’s surface. But compositionally, Organa was unique. The crater and portions of the surrounding area showed infrared absorption at wavelengths of about 2.2 microns (LEISA sees between 1.25 and 2.5 microns). 2.2 microns point to an area rich in frozen ammonia.
Telescopes first noticed ammonia absorption on Charon in 2000, but never at levels like this. Why so much ammonia? The New Horizons science team have a few ideas. The crater could be younger. Or the impact revealed an area of ammonia-rich subsurface ice. Maybe whatever made the crater delivered the ammonia.
Bill McKinnon, deputy lead for the New Horizons Geology, Geophysics and Imaging team, says it could even explain how Charon’s surface looks today. “Concentrated ammonia is a powerful antifreeze on icy worlds, and if the ammonia really is from Charon’s interior it could help explain the formation of Charon’s surface by cryovolcanism, via the eruption of cold, ammonia-water magmas.”
New Horizons continues to downlink its data back to Earth. The data gathered by LEISA and New Horizons’ other instruments will fuel discoveries for years.