High-resolution
MVIC view of Pluto in enhanced color, illustrating variations in surface composition
The geology of Pluto consists of the characteristics of the surface, crust, and interior of Pluto. Because of Pluto's distance from Earth, in-depth study from Earth is difficult. Because of this, many details about Pluto remained unknown until 14 July 2015, when New Horizons flew through the Pluto system, and onwards, because of the time required to send all the data to Earth.[1] When it did, Pluto was found to have a lot of geologic diversity, with New Horizons team member Jeff Moore saying that it "is every bit as complex as that of Mars” [2]
Surface
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Polygonal feature north of the dark equatorial regions on Pluto
(11 July 2015)
The portions of Pluto's surface mapped by
New Horizons. Center is 180 degrees longitude (diametrically opposite the moon Charon).
Pluto's surface is composed of more than 98 percent nitrogen ice, with traces of methane and carbon monoxide.[3] The face of Pluto oriented toward Charon contains more methane ice, whereas the opposite face contains more nitrogen and carbon monoxide ice.[4]
Maps produced from images taken by the Hubble Space Telescope (HST), together with Pluto's lightcurve and the periodic variations in its infrared spectra, indicate that Pluto's surface is very varied, with large differences in both brightness and color,[5] with albedos between 0.49 and 0.66.[6] Pluto is one of the most contrastive bodies in the Solar System, with as much contrast as Saturn's moon Iapetus.[7] The color varies between charcoal black, dark orange and white.[8] Pluto's color is more similar to that of Io with slightly more orange, significantly less red than Mars.[9] New Horizons found that Pluto's surface age is equally variable, with ancient, dark, mountainous terrain (such as Cthulhu) being found alongside the bright, flat, effectively craterless Sputnik Planum and various terrains of intermediate age and color.
Pluto's surface color has changed between 1994 and 2003: the northern polar region has brightened and the southern hemisphere has darkened.[8] Pluto's overall redness has also increased substantially between 2000 and 2002.[8] These rapid changes are probably related to seasonal condensation and sublimation of portions of Pluto's atmosphere, amplified by Pluto's extreme axial tilt and high orbital eccentricity.[8]
Distribution of over 1000 craters of all ages on Pluto. The variation in density indicates a long history of varying geological activity.
Geologic map of Sputnik Planum and surroundings (
context), with convection cell margins outlined in black
Soft-ice plains and glaciers
Sputnik Planum appears to be composed of ices more volatile, softer and more dense than the water-ice bedrock of Pluto, including nitrogen, carbon monoxide and methane ice.[10] A polygonal convection cell structure is visible over much of the planum. No craters have been found, indicating that its surface must be less than 10 million years old.[11] Glaciers of what is probably nitrogen ice can be seen flowing from the planum into adjacent depressions and craters. Nitrogen from the plain appears to have been carried via the atmosphere and deposited in a thin layer of ice on uplands to the east and south of the plain, forming the large bright eastern lobe of Tombaugh Regio. Glaciers appear to be flowing back into the planum through valleys from these eastern highlands.
Localization of frozen
carbon monoxide in Sputnik Planum (shorter contours represent higher concentrations).
Polygonal ice patterns in southern Sputnik Planum (
context) due to convection. Dark spots in the troughs at lower left are pits.
[12]
Closeup view of sublimation pits (
context) in Sputnik Planum
Additional views of Sputnik Planum sublimation pits (
context); some (left image) have dark material within
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The northern edge of Sputnik Planum ( context), with indications of nitrogen ice flowing into and filling adjacent depressions. |
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Nitrogen ice glaciers flow from uplands through valleys into east Sputnik Planum ( context). Arrows indicate valley sides (which are 3 to 8 km apart) and the flow front in the planum. |
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Nitrogen ice glaciers flowing into the eastern margin of the planum (similar reprojected backlit view highlighting flow lines).
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Water-ice mountains
Mountains several kilometres high have been found along the southwestern and southern edges of Sputnik Planum. Water ice is the only ice detected on Pluto that is strong enough at Plutonian temperatures to support such heights.
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Pluto - water ice distribution (false color; rel 29 January 2016
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Regions where water ice has been detected (blue regions)
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Ancient cratered terrain
Cthulhu Regio and other dark areas have many craters and signatures of methane ice. The dark red color is thought to be due to tholins falling out of Pluto's atmosphere.
Northern latitudes
The mid-northern latitudes display a variety of terrain reminiscent of the surface of Triton. A polar cap consisting of methane ice "diluted in a thick, transparent slab of nitrogen ice" is somewhat darker and redder.[14]
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Distribution of methane ice on Pluto. Bright green is the polar cap; bright red is Balrog Regio. |
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Map of methane ice abundance, which shows striking regional differences. Stronger methane absorption indicated by the brighter purple colors here, and lower abundances shown in black.
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Indications of complex geological features north of the dark equatorial regions
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The western part of Pluto's northern hemisphere consists of an extensive, highly distinctive set of 500-meter-high mountains informally named Tartarus Dorsa; the spacing and shape of the mountains looks similar to scales or tree bark. The method of their formation is unknown, though it has been speculated that they may be composed of methane clathrates that formed in the protosolar nebula.[15] Cutting through both Tartarus Dorsa and Pluto's heavily cratered northern terrain is a set of six canyons radiating from a single point; the longest, informally named Sleipnir Fossa, is over 580 kilometers long. These chasms are thought to have originated from pressures caused by material upwelling at the center of the formation.[16]
Possible cryovolcanism
When New Horizons first sent back data from Pluto, Pluto was thought to be losing hundreds of tons of its atmosphere an hour to ultraviolet light from the Sun; such an escape rate would be too great to be resupplied by comet impacts. Instead, nitrogen was thought to be resupplied by either cryovolcanism or geysers bringing it to the surface. Images of structures that imply upwelling of material from within Pluto, and streaks possibly left by geysers, support this view.[12][17] Subsequent discoveries suggest that Pluto's atmospheric escape was overestimated by several thousand times and thus Pluto could theoretically keep its atmosphere without geological assistance, though evidence of ongoing geology is still strong.[18]
Two possible cryovolcanoes, provisionally named Wright Mons and Piccard Mons, have been identified in topographic maps of the region south of Sputnik Planum, near the south pole. Both are over 150 km across and at least 4 km high, the tallest peaks known on Pluto at present. They are lightly cratered and thus geologically young, although not as young as Sputnik Planum. They are characterized by a large summit depression and hummocky flanks. This represents the first time large potentially cryovolcanic constructs have been clearly imaged anywhere in the Solar System.[19][20][21]
3D map showing Wright Mons (above) and Piccard Mons
Internal structure
Pluto's theoretical structure
[22]
- 1. Frozen nitrogen[3]
- 2. Water ice
- 3. Rock
Pluto's density is 1.87 g/cm3.[23] Because the decay of radioactive elements would eventually heat the ices enough for the rock to separate from them, scientists think that Pluto's internal structure is differentiated, with the rocky material having settled into a dense core surrounded by a mantle of water ice.[24]
The diameter of the core is hypothesized to be approximately 1700 km, 70% of Pluto's diameter.[22] It is possible that such heating continues today, creating a subsurface ocean layer of liquid water some 100 to 180 km thick at the core–mantle boundary.[22][24][25] The DLR Institute of Planetary Research calculated that Pluto's density-to-radius ratio lies in a transition zone, along with Neptune's moon Triton, between icy satellites like the mid-sized moons of Uranus and Saturn, and rocky satellites such as Jupiter's Io.[26]
See also
References
External links
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