The geography of Pluto entails the delineation and characterization of regions on Pluto. Plutonian geography is mainly focused on what is called physical geography on Earth; that is, the distribution of physical features across Pluto and their cartographic representations. On 14 July 2015, the New Horizonsspacecraft became the first spacecraft to fly by Pluto. During its brief flyby, New Horizons made detailed geographical measurements and observations of Pluto and its moons.
Orientation
Pluto may be defined as having retrograde rotation and an axial tilt of 60 degrees, or prograde rotation and a tilt of 120 degrees. Following the latter convention, the hemisphere currently in daylight is the northern one, with much of the southern hemisphere in darkness. This is the convention used by the International Astronomical Union and the New Horizons team, and their maps put the sunlit hemisphere on top. However, older sources may define Pluto's rotation as retrograde and therefore the sunlit side as the southern hemisphere. East and west are also swapped between the two conventions.
Topographical features
The following names were originally proposed by the New Horizons discovery team. These names were variously taken from historical figures involved in the study of Pluto, notable space exploration missions, and a variety of chthonic deities or demons, some from ancient mythology and others from modern popular culture. While several of these names have been canonized by the IAU as of 2017, most remain informal classifications that have yet to be considered.
Tombaugh Regio
Tombaugh Regio, nicknamed The Heart, is a large, light-colored region in the shape of a heart named after the discoverer of Pluto, Clyde Tombaugh. Two lobes of the heart are distinct geological features sharing a bright appearance, with the western lobe smoother than the eastern lobe. The heart is about across. The region contains mountains made of water ice, Hillary Montes and Tenzing Montes, along its southwestern edge. The lack of craters suggests that its surface there is less than 100 million years old and hence that Pluto is probably geologically active. Subsequent data indicated that features near the edges of the region show evidence of ice flow such as glaciers, and light material overlying the darker material at the eastern edge of Cthulhu Macula.
A series of semi-regularly spaced dark spots with irregular boundaries are nicknamed the Brass Knuckles. They average about in diameter and are located along the equator between the Heart and the tail of the Whale. The brass knuckles are separated from one another by tall uplands. There are also many canyons running through them and through the surrounding mountains that are hundreds of miles long and several miles deep. From west to east, the Knuckles are:
Cthulhu Macula, nicknamed The Whale after its shape, is an elongated, dark region along Pluto's equator named after the fictional deity from the works of H. P. Lovecraft. It is long and is the largest dark feature on Pluto. It is the largest of the dark regions that span Pluto's equator. The dark color of the area is speculated to be the result of a "tar" made of complex hydrocarbons called tholins covering the surface, formed from methane and nitrogen in the atmosphere interacting with ultraviolet light and cosmic rays. The presence of a large number of craters within Cthulhu indicates that it is perhaps billions of years old, in contrast to the adjacent bright, craterless Sputnik Planitia, which may be as little as 100 million years old.
The Donut
A bright, ring-shaped feature about across located near the tail of the "Whale" in low-resolution images is nicknamed the "Donut". It does not appear as a ring in higher-resolution images.
Dune fields
In the Western part of Sputnik Planitia near Al-Idrisi Montes there are fields of transverse dunes formed by the winds, which blow from the center of Sputnik Planitia in the direction of surrounding mountings. The dune wavelengths are in the range of 0.4–1 km and they are likely consists of methane ice particles 200–300 μm in size. The particles are lofted above the surface when the nitrogen icesublimates under solar irradiation. After that they are moved by gentle winds blowing with 1–10 m/s speeds despite generally low atmospheric pressure of about 15 μbar.
The Working Group for Planetary System Nomenclature of the International Astronomical Union is responsible for assigning official names to surface features on Pluto. On 7 September 2017, the first 14 names have been officially approved by the IAU. As of August 2015, the New Horizons science team derives informal names from the following themes: explorers, space missions, spacecraft, scientists and engineers; fictional explorers, travellers, vessels, destinations and origins; authors and artists who have envisioned exploration; and fictional underworlds, underworld beings, and travellers to the underworld. The New Horizons science team has invited members of the public to propose names and vote on them before the spacecraft's arrival.
