User:ArkHyena/Drafts/Draftspace1

Notes and resources

PLUTO SYSTEM AFTER NEW HORIZONS

• Pluto forms closer in, Neptune migrates 5-10 AU; Pluto captured in MMR beyond 28 AU; differences w CCKBOs p.547
• 35 cm accumulation of dark deposits over 100 myr p. 109

CURRENT DRAFT: Geology of Pluto rewrite

High-resolution New Horizons image showing the chaotic, blocky Al-Idrisi Montes near the western fringes of Sputnik Planitia's convecting glaciers

The geology of Pluto consists of the characteristics of the surface, crust, and interior of the dwarf planet Pluto. With a mean diameter of 2,376.6±1.6 km, Pluto is the largest known object beyond Neptune and the largest known dwarf planet in the Solar System, though Eris is significantly more massive. Pluto's density of 1.85 g/cm³ indicates that Pluto is composed of a significant amount of water, differentiated into an outer icy crust and a probable internal ocean of liquid water that surrounds a rocky core. More volatile compounds such as nitrogen, methane, and ammonia cover much of Pluto's surface, shaping and eroding its terrain. These volatiles also sublimate into Pluto's thin atmosphere, driving weather and climate.

Because of Pluto's great distance from Earth, many details about Pluto remained unknown until 14 July 2015, when the New Horizons spacecraft flew through the Pluto system and began transmitting data back to Earth. When it did, Pluto was found to have remarkable geologic diversity, with New Horizons team member Jeff Moore saying that it "is every bit as complex as that of Mars". The final New Horizons Pluto data transmission was received on 25 October 2016.

Geological history

Pluto is a member of the Kuiper belt, an extensive disk of debris which survived the formation of the Solar System. As such, its formation and history is closely tied to other Kuiper belt objects (KBOs). However, between Pluto's discovery in 1930 and the discovery of the classical KBO 15760 Albion in 1992, Pluto remained the only known object beyond Neptune's orbit. Its elliptical orbit crosses the orbit of Neptune, at times bringing it closer to the Sun than Neptune. As a result, a prominent early hypothesis of Pluto's origin forwarded by astronomer R. A. Lyttleton in 1936 proposed that Pluto was originally a large moon of Neptune along with Triton; the hypothesis argued that interactions between Pluto and Triton ejected Pluto into its elliptical orbit and turned Triton's orbit retrograde. However, this early hypothesis was later refuted by W. B. McKinnon in 1984 as Triton's mass had been historically overestimated. Instead, McKinnon proposed that both Triton and Pluto are icy planetesimals from the Solar System's early history, with Triton later being captured into Neptune orbit. Understanding of Pluto's origin and history has since grown more thorough, particularly following Charon's discovery in 1978, the charting of the Kuiper Belt since the 1990's, and the New Horizons flyby in 2015.

Formation

Prior to the flyby of New Horizons, the nature of Pluto's formation was unclear and debated. Models of Pluto's early history can be divided into hot start and cold start models. Hot start models advocate for a rapid and violent formation which led to an initial era of rapid internal expansion and an ongoing era of more gradual expansion as Pluto's internal ocean freezes. Cold start models, in contrast, advocate for a slower, more gradual formation; Pluto's internal ocean only formed once enough radiogenic heat built up, leading to an initial era of compression as part of its icy mantle melts.

Initial models of KBO formation predicted very slow growth, taking hundreds of millions of years to create Pluto-sized objects, conflicting with the hot start scenario. More recent models, however, suggest that streaming instability in the Solar protoplanetary disc initiated a very rapid era of accretion into Pluto-sized objects, taking less than 100,000 years to grow planetesimals from ~300 km in diameter to ~1,000 km in diameter. This rapid accretion stage is in agreement with a hot start scenario, and a delayed-onset (after significant amounts of ²⁶Al decayed) rapid accretion stage additionally reconciles the differentiated nature of dwarf planets such as Pluto and the porous, poorly-differentiated nature of smaller KBOs.

• more specifics of timeframe in this paragraph, incl. neptune resonance capture etc.

Charon impact

Pluto hosts a system of five satellites; Charon, the largest moon of Pluto and roughly half its size, is massive enough that the system's barycenter lies well outside of Pluto. Four smaller circumbinary moons revolve around Pluto and Charon. Charon and the outer moons are thought to be the result of a giant impact between two large similarly-sized planetesimals early in the Solar System's history, likely before Neptune and Uranus began migrating outwards. Following the giant impact, Pluto was likely left rapidly rotating, whilst Charon may have followed a highly-eccentric orbit. The energy from the giant impact would have heated Pluto intensely, possibly raising its global temperature by 50-75K; tidal heating from Charon as its orbit around Pluto dampened would have imparted additional heat. By the end of Charon's orbital evolution around Pluto, both worlds would likely have been differentiated.

• brief description of pluto's four moons and possible collisional family

Subsequent evolution

• RTS formation and subsequent continuation (as "ancient tectonics")
• Sputnik impact and true polar wander (initially a negative anomaly, later infilling turns it into a positive anomaly)
• continued rifting due to TPW and ocean freezing (as "sputnik-related tectonics")
• brief discussion of climate cycles, incl. possible past extensive glacial period up until modern times (lots of regions indicate past glaciation, yet are not currently glaciated; where did N2 go?)

Surface

Pluto's surface is highly diverse. Pluto is quite reflective, with an average Bond albedo of 0.72, reflecting 72% of all electromagnetic radiation that strikes its surface. However, its surface is unusually contrastive in color, with astronomer Marc Buie comparing the level of contrast on Pluto to Saturn's famously contrastive moon Iapetus.

• 
  Map of Pluto's surface in black and white, from New Horizons imagery
• 
  Map of identified impact craters on Pluto as of 2023

Polar caps

Pluto's higher latitudes are largely covered in a layer of deposited soft ice, which forms its extensive polar ice caps.

Sputnik Planitia

Main article: Sputnik Planitia

Sputnik Planitia is a massive elliptical depression located near Pluto's anti-Charon point.

Western Sputnik mountains

Along the western edges of Sputnik Planitia lie an extensive series of mountain ranges.

Tectonics

Ridge-trough system

A great, ancient tectonic system of troughs, plateaus, and mountain ranges hundreds of kilometers wide termed the ridge-trough system (RTS) cuts a roughly north to south great circle around Pluto, following between the 145°–165° E meridians. The RTS is extends for at least 3,200 kilometers across Pluto's surface and is 300 to 400 kilometers wide for much of its length, though it appears to extend further south into the unimaged regions of Pluto and a large section is interrupted by the Sputnik Planitia basin. That it is so significantly eroded and superceded by the Sputnik Planitia basin indicates that it is the oldest large-scale feature identified on Pluto's surface.

Internal structure

Pluto's density is 1.853 ± 0.004 g/cm³

See also

• List of geological features on Pluto

External links

• Pluto viewed through the years (NASA; GIF animation; 15 July 2015).