Fresh images display Pluto's atmosphere in a new light
The first color imagesreturned of Pluto by NASA's New Horizons spacecraft reveals blueskies and surface water-ice deposits. Previous non-color images ofthe dwarf planet's tenuous atmosphere have displayed a surprisinglycomplex multilayer structure, and the new color images have allowedscientists to deduce the composition of the haze.
An analysis of the newimage snapped by the spacecraft's Ralph/Multispectral Visible ImagingCamera (MVIC) has led scientists to theorize that the observedcomposition of Pluto's atmosphere arises from sunlight acting as thecatalyst for a chemical reaction between nitrogen (N) and methane(CH4).
In basic terms, thesunlight breaks down and ionizes the CH4 and N molecules, freeing them to react and form complexnegative and positively charged ions, which recombine to create verylarge molecules known as macromolecules. The macromolecules grow to form particles known as tholins.
This process, which isvery similar to the one taking place in the atmosphere present aroundthe Saturnian moon Titan, results in Pluto's blue haze having a soot-like consistency. NASA scientists note that the individual particlesare most likely grey or red, but the manner in which sunlight isscattered by the haze throws off a blueish hue.
"That striking bluetint tells us about the size and composition of the haze particles,"explains New Horizons science team researcher Carly Howett, of theSouthwest Research Institute (SwRI), Boulder, Colorado. "A blue skyoften results from scattering of sunlight by very small particles. OnEarth, those particles are very tiny nitrogen molecules. On Plutothey appear to be larger — but still relatively small — soot-likeparticles we call tholins."
It is believed thatvolatile gasses condense on the surface of the tholin particles,coating them with ice. When these icy particles reach the dwarfplanet's surface, they contribute to the reddish color that has beenobserved across Pluto's surface, and on the north pole of her largemoon Charon.
Not content to leave uswith the knowledge that Pluto hosts blue skies, the New Horizons teamhad one more surprise in store. The newest release of images from theNew Horizons probe highlights significant deposits of water ice onthe surface of the dwarf planet.
Data harvested by thespacecraft's Ralphspectral composition mapper hasrevealed numerous small deposits spread across the dwarf planet'ssurface. The data appears to show concentrations of water ice inareas synonymous with the reddish regions discolored by theaforementioned tholin particles, though the relationship between thetwo phenomena has yet to be explained.
"Large expanses ofPluto don’t show exposed water ice," states science team memberJason Cook, of SwRI, "because it’s apparently masked by other,more volatile ices across most of the planet. Understanding why waterappears exactly where it does, and not in other places, is achallenge that we are digging into."