The blue halo around Pluto (above) is haze extending to altitudes of more than 200 kilometres and settling in layers in Pluto’s atmosphere.
Scientists believe the bright blue hue is a photochemical smog, which works in a similar way to the molecules that make the Earth’s blue sky.
When sunlight hits the molecules in Pluto’s atmosphere, such as methane, a complex blend of hydrocarbons is produced, which form small particles that scatter the sunlight into the blue wavelength.
This photo is colour-enhanced but shows an approximate true colour image at a resolution of one kilometre per pixel. It was built from four overlaying photos taken from New Horizons’ Long Range Reconnaissance Imager (LORRI).
Charon’s Grand Canyon
Charon, Pluto’s largest moon, is a fascinating celestial body in its own right. Above, we see a canyon system sliced into its surface.
At 700 kilometres long and an estimated nine kilometres deep, Charon’s canyon is around 250 kilometres longer than the Grand Canyon and five times as deep.
Informally named Argo Chasma, its sheer cliff drops rival those on Uranus’ moon Miranda, which are considered the highest known cliff faces in the solar system.
The photo was taken by New Horizons’ LORRI from a distance of 466,000 kilometres.
Surface patterns on Sputnik Planum
Pluto’s frozen “heart”, known as the Tombaugh Regio, is not as smooth as scientists once thought it was, as the textured surface patterns that were revealed after NASA’s New Horizons team processed a close-up shot.
The image on the left is an enhanced-colour photo taken 18 minutes before New Horizons’ closest approach. The image on the right is a “scattering map” of the same region.
The scattering map is where two photos at two different angles were combined, where the direction of the sun’s reflection depends on whether the terrain is rough or smooth.
Smooth terrain reflects light away from the sun, whereas rough terrain reflects it back toward the sun, exposing the textured pattern for the first time.
Scientists believe the relatively smooth surface of Pluto’s heart is from a convective flow. This is where warmer nitrogen ice rises to the top and spreads outward. According to NASA, it’s akin to a cosmic lava lamp.
Scientists believe the patterns are a consequence of this lava lamp process, although they aren’t yet sure how.
A mountain range in Pluto’s heart
Flanking Pluto’s frozen nitrogenous heart is an icy mountain range, about the same height range as America’s Appalachian Mountains at one to 1.5 kilometres.
In the photo above, you can see the mountainous region lies between a smooth icy plain and dark, cratered terrain on the southwestern side of the Tombaugh Regio.
The photo was taken by LORRI on the New Horizons’ 14 July fly-by.
Sunken icy plains
A shaded relief view of the region surrounding the left side of Pluto’s heart-shaped feature shows an icy plain on average three kilometres lower than the surrounding terrain.
Along the western edge are blocks of water ice “floating” in softer, denser solid nitrogen.
Topographic maps of Pluto such as this have been produced using data from the 14 July 2015 fly-by. They are derived from digital stereo-image mapping tools that measure the parallax of surface features.
A global perspective
This updated black and white global map of Pluto includes all resolved images of Pluto’s surface acquired between 7 and 14 July 2015, at pixel resolutions ranging from 30 kilometres on the Charon-facing hemisphere (left and right edges of the map) to 235 metres on the hemisphere facing New Horizons during the spacecraft’s closest approach on 14 July (map centre).
The NASA science team is working on improved colour maps.
Anthea Batsakis is a freelance journalist in Melbourne, Australia.