Thegeography of Pluto refers to the study and mapping of physical features across thedwarf planetPluto. On 14 July 2015, theNew Horizonsspacecraft became the first spacecraft tofly by Pluto.[1][2] During its brief flyby,New Horizons made detailed geographical measurements and observations of Pluto and itsmoons.[3]
Pluto may be defined as havingretrograde rotation and an axial tilt of 60 degrees, or prograde rotation and a tilt of 120 degrees. Following the latter convention (theright-hand rule), the hemisphere currently in daylight is the northern one, with much of the southern hemisphere in darkness. This is the convention used by theInternational Astronomical Union (IAU) and theNew 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.[4]
Theprime meridian of Pluto is defined as the longitude facingCharon.[5]
The following names were originally proposed by theNew 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,[6] most remain informal classifications that have yet to be considered.
Tombaugh Regio (nicknamed "The Heart") is a large, light-colored topographical region, formed in theshape of a heart, named after the modern discoverer of Pluto,Clyde Tombaugh. The two top lobes of the heart are distinct geological features, both having a bright and whiteish appearance, with the western lobe (calledSputnik Planitia – a vast plain ofnitrogen and other ices) being smoother than the eastern lobe.[7] The heart is about 1,590 km (990 mi) across. The region contains two 3,400 m (11,000 ft)peaks composed of water-ice along its southwestern edge,Hillary Montes andTenzing Montes. The lack of craters in the region suggests that its surface is less than 100 million years old, hence the speculation that Pluto is probably geologically active.[8] Subsequent data indicated that features near the western edges of the region (an area about the size ofTexas) show evidence of "exotic ice flow", similar to melting glaciers, rich in methane, carbon monoxide, and nitrogen ices. Potentially recent glacial activity, nearCthulhu Macula, is suggested by the presence of lighter-hued material overlaid on top of darker, more ancient portions; according to Lillian Gipson at NASA, "...In the southernmost region of the heart, adjacent to the dark equatorial region, it appears that ancient, heavily-cratered terrain (informally named “Cthulhu Regio”) has been invaded by much newer icy deposits."[9]
A series of semi-regularly spaced dark spots with irregular boundaries are nicknamed theBrass Knuckles. They average about 480 km (300 mi) in diameter and are located along the equator between the Heart and the tail of the Whale.[10][11] 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.[12] From west (south of Tombaugh Regio) to east (west of the Whale's tail), the Knuckles are:[13][14]
Belton Regio (formerly calledCthulhu Macula orCthulhu Regio),[16] nicknamedThe Whale after its shape, is an elongated, dark region along Pluto's equator named in honor of astronomerMichael J. Belton,[17] and was informally named after the fictionaldeity from the works ofH. P. Lovecraft. It is 2,990 km (1,860 mi) long and is the largest dark feature on Pluto.[18] It is the largest of the dark regions (Brass Knuckles) that span Pluto's equator.[16] The dark color of the area is speculated to be the result of a "tar" made of complex hydrocarbons calledtholins covering the surface, formed from methane and nitrogen in the atmosphere interacting with ultraviolet light and cosmic rays.[19][20][21]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, craterlessSputnik Planitia, which may be as little as 100 million years old.[22]
In the Western part of Sputnik Planitia nearAl-Idrisi Montes, there are fields oftransverse 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 likely consist of methane ice particles 200–300 μm in size. The particles are lofted above the surface when the nitrogen icesublimates undersolar 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.[23]
TheWorking Group for Planetary System Nomenclature of the International Astronomical Union (IAU) is responsible for assigning official names to surface features on Pluto. On 7 September 2017, the first 14 names were officially approved by the IAU.[6]
As of August 2015, theNew Horizons science team derivesinformal 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 fictionalunderworlds, underworld beings, and travellers to the underworld. TheNew Horizons science team invited members of the public to propose names and vote on them before the spacecraft's arrival.[24]
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| Candidate (for TNOs, D+1σ ≥ 700 km or H ≤ 4.0) |
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