Temperature correction, resonance self-shielding, and flux weighting to provide problem-dependent microscopic and macroscopic multigroup cross section data integrated with computational sequences, but also available for stand-alone analysis Library used throughout SCALE that provides individual nuclides; elements with tabulated natural abundances; compounds, alloys, mixtures, and fissile solutions commonly encountered in engineering practice Triton's western hemisphere consists of a strange series of fissures and depressions known as "cantaloupe terrain" because it resembles the skin of a cantaloupe melon. Although it has few craters, it is thought that this is the oldest terrain on Triton. [68] It probably covers much of Triton's western half. [7]

Two types of mechanisms have been proposed for Triton's capture. To be gravitationally captured by a planet, a passing body must lose sufficient energy to be slowed down to a speed less than that required to escape. [7] An early theory of how Triton may have been slowed was by collision with another object, either one that happened to be passing by Neptune (which is unlikely), or a moon or proto-moon in orbit around Neptune (which is more likely). [7] A more recent hypothesis suggests that, before its capture, Triton was part of a binary system. When this binary encountered Neptune, it interacted in such a way that the binary dissociated, with one portion of the binary expelled, and the other, Triton, becoming bound to Neptune. This event is more likely for more massive companions. [13] This hypothesis is supported by several lines of evidence, including binaries being very common among the large Kuiper belt objects. [29] [30] The event was brief but gentle, saving Triton from collisional disruption. Events like this may have been common during the formation of Neptune, or later when it migrated outward. [13] Surface gravity derived from the mass m, the gravitational constant G and the radius r: G m r 2 {\displaystyle {\frac {Gm}{rTriton's south polar region is covered by a highly reflective cap of frozen nitrogen and methane sprinkled by impact craters and openings of geysers. Little is known about the north pole because it was on the night side during the Voyager 2 encounter, but it is thought that Triton must also have a north polar ice cap. [44] Stochastic uncertainty quantification in results based on uncertainties in nuclear data and input parameters Simulated 2D and 3D analysis for light water reactor spent fuel assemblies (isotopic activation, depletion, and decay for light water reactor fuel assemblies) The high plains found on Triton's eastern hemisphere, such as Cipango Planum, cover over and blot out older features, and are therefore almost certainly the result of icy lava washing over the previous landscape. The plains are dotted with pits, such as Leviathan Patera, which are probably the vents from which this lava emerged. The composition of the lava is unknown, although a mixture of ammonia and water is suspected. [7]

In the 1990s, various observations from Earth were made of the limb of Triton using the occultation of nearby stars, which indicated the presence of an atmosphere and an exotic surface. Observations in late 1997 suggest that Triton is heating up and the atmosphere has become significantly denser since Voyager 2 flew past in 1989. [48]extended step characteristic transport with flexible geometry applied to neutronics analysis, especially within the TRITON sequences Triton's revolution around Neptune has become a nearly perfect circle with an eccentricity of almost zero. Viscoelastic damping from tides alone is not thought to be capable of circularizing Triton's orbit in the time since the origin of the system, and gas drag from a prograde debris disc is likely to have played a substantial role. [4] [5] Tidal interactions also cause Triton's orbit, which is already closer to Neptune than the Moon is to Earth, to gradually decay further; predictions are that 3.6billion years from now, Triton will pass within Neptune's Roche limit. [26] This will result in either a collision with Neptune's atmosphere or the breakup of Triton, forming a new ring system similar to that found around Saturn. [26] Capture [ edit ] The Kuiper belt (green), in the Solar System's outskirts, is where Triton is thought to have originated. Triton's orbit is associated with two tilts, the obliquity of Neptune's rotation to Neptune's orbit, 30°, and the inclination of Triton's orbit to Neptune's rotation, 157° (an inclination over 90° indicates retrograde motion). Triton's orbit precesses forward relative to Neptune's rotation with a period of about 678 Earth years (4.1 Neptunian years), [4] [5] making its Neptune-orbit-relative inclination vary between 127° and 173°. That inclination is currently 130°; Triton's orbit is now near its maximum departure from coplanarity with Neptune's. Recent uncertainties in nuclear data for neutron interaction, fission product yields, and decay data for use in TSUNAMI tools and Sampler

All the geysers observed were located between 50° and 57°S, the part of Triton's surface close to the subsolar point. This indicates that solar heating, although very weak at Triton's great distance from the Sun, plays a crucial role. It is thought that the surface of Triton probably consists of a translucent layer of frozen nitrogen overlying a darker substrate, which creates a kind of "solid greenhouse effect". Solar radiation passes through the thin surface ice sheet, slowly heating and vaporizing subsurface nitrogen until enough gas pressure accumulates for it to erupt through the crust. [7] [46] A temperature increase of just 4 K above the ambient surface temperature of 37K could drive eruptions to the heights observed. [59] Although commonly termed "cryovolcanic", this nitrogen plume activity is distinct from Triton's larger-scale cryovolcanic eruptions, as well as volcanic processes on other worlds, which are powered by internal heat. CO 2 geysers on Mars are thought to erupt from its south polar cap each spring in the same way as Triton's geysers. [62] Eigenvalue Monte Carlo codes applied in many computational sequences for multigroup and continuous energy neutronics analysis Polar cap, plains and ridges [ edit ] Triton's bright south polar cap above a region of cantaloupe terrain

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In 1997, observations from Earth were made of Triton's limb as it passed in front of stars. These observations indicated the presence of a denser atmosphere than was deduced from Voyager 2 data. [48] Other observations have shown an increase in temperature by 5% from 1989 to 1998. [49] These observations indicated Triton was approaching an unusually warm southern hemisphere summer season that happens only once every few hundred years. Theories for this warming include a change of frost patterns on Triton's surface and a change in ice albedo, which would allow more heat to be absorbed. [50] Another theory argues that temperature changes are a result of the deposition of dark, red material from geological processes. Because Triton's Bond albedo is among the highest in the Solar System, it is sensitive to small variations in spectral albedo. [51] Surface features [ edit ] Interpretative geomorphological map of Triton Main article: Atmosphere of Triton Artist's impression of Triton, showing its tenuous atmosphere just over the limb. The Voyager 2 probe in 1989 observed a handful of geyser-like eruptions of nitrogen gas and entrained dust from beneath the surface of Triton in plumes up to 8km high. [33] [59] Triton is thus, along with Earth, Io, Europa and Enceladus, one of the few bodies in the Solar System on which active eruptions of some sort have been observed. [60] The best-observed examples are named Hili and Mahilani (after a Zulu water sprite and a Tongan sea spirit, respectively). [61] Triton was discovered by British astronomer William Lassell on October 10, 1846, [17] just 17days after the discovery of Neptune. When John Herschel received news of Neptune's discovery, he wrote to Lassell suggesting he search for possible moons. Lassell discovered Triton eight days later. [17] [18] Lassell also claimed for a period [h] to have discovered rings. [19] Although Neptune was later confirmed to have rings, they are so faint and dark that it is not plausible he saw them. A brewer by trade, Lassell spotted Triton with his self-built 61cm (24in) aperture metal mirror reflecting telescope (also known as the "two-foot" reflector). [20] This telescope was donated to the Royal Observatory, Greenwich in the 1880s, but was eventually dismantled. [20]

Recent neutron, gamma and coupled neutron/gamma nuclear data libraries in continuous-energy and several multigroup structures for use in all transport modulesTwo large cryolava lakes on Triton, seen west of Leviathan Patera. Combined, they are nearly the size of Kraken Mare on Titan. These features are unusually crater free, indicating they are young and were recently molten.