and Pluto has certainly provided many surprises. One of the biggest has been its‘ astonishing variety of landscapes’, from the 1000km-wide uncratered plain of Sputnik Planum, bounded by mountainous regions, such as Al-Idrisi Montes and Hillary Montes, to cratered plains mantled with either brighter ices( north polar region) or darker deposits( Cthulhu Regio and Krun Macula), and rugged uplands marked with pits or elongated, raised‘ blades’ on the eastern section of Tombaugh Regio. This diversity provides evidence of a long and complex geological history, with some of it unexpectedly recent.
These features can be identified on the composite global map( Figure 6), created from images taken during approach and flyby, which shows the main regions, together with their provisional names( these have yet to receive formal approval by the International Astronomical Union).
Figure 6: Informal names for regions on Pluto, based on a public naming campaign endorsed by the IAU, in partnership with NASA’ s New Horizons mission and the SETI Institute. Credit: NASA / JHUAPL / SwRI / SETI Institute
To understand Pluto’ s surface, we must remember that, at a distance of 30 to 50 times Earth’ s distance from the sun, Pluto is one of the coldest large bodies in the solar system with surface temperatures ranging from about only 33K(-240 ° C) to 55K(-218 ° C). Its surface composition and chemistry are quite different from those on Earth, although they do operate in a way to bring about analogous geological processes. So, rather than the Earth’ s rocky mountains floating on a mantle of magma, we find what Leslie Young describes as‘ platoons of water-ice mountains floating in seas of frozen nitrogen – water is like the bedrock here.’ It is the nitrogen, also the dominant component of Pluto’ s atmosphere, which appears to be involved in the most surprising surface processes observed- active glacial flow and the resurfacing of Sputnik Planum. This plain is located in what is probably an ancient impact basin, given the arcuate nature of the mountains bordering it on three sides.
Figure 7 shows the north-west edge of Sputnik Planum, where it meets Al-Idrisi Montes. There are flow patterns towards the mountains at the margin. There is also clear evidence of glacial flow channels in the oblique angle view of Sputnik Planum shown in Figure 8. At the surface nitrogen ice, which is structurally-weak compared to the rock-hard water ice, has a low enough viscosity to flow at the temperatures found on Pluto’ s surface. This surface flow is analagous to that of glaciers on Earth, with the volatiles flowing‘ more slowly than silly putty but …. faster than glacial water ice on Earth.’
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