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By AARON SKETCHLEY (aaronsketch@HOTdelete_thisMAIL.com) 2019.12.15 Ver 3.6

Official Setting information is in darkgreen. Extended Universe information is in steelblue.

The Solar System - Trans-Neptunian & Farthest Regions

  • Inner Solar System
  • Asteroid Belt
  • Outer Solar System
    30 AU
  • Kuiper Belt
    35 AU
  • Orcus
  • 2003 VS2
  • (D) Pluto
  • Ruins of South Ataria Island
  • 2003 AZ84
  • Ixion
  • Huya
  • 2005 RN43
  • 2002 MS4
  • Salacia
    40 AU
  • 2004 GV9
  • 2002 UX25
  • Varuna
  • (D) Haumea
  • Quaoar
  • 2002 TX300
  • 2005 UQ513
    45 AU
  • 2010 KZ39
  • Chaos
  • (D) Makemake
  • Varda
  • 2010 RF43
  • 2002 AW197
  • 2007 JJ43
  • 2003 QX113
    50 AU
  • 2001 UR163
  • Kuiper Gap
  • Scattered Disc
    55 AU
  • 2002 TC302
  • 2004 XR190 "Buffy"
  • 65 AU
  • 2007 OR10
  • 2006 QH181
  • (D) Eris
  • 2010 EK139
    70 AU
  • 2007 UK126
    75 AU
  • 2010 RE64
    80 AU
  • 1996 TL66
    85 AU
  • Termination Shock
  • 90 AU
  • Heliosheath
    95 AU
  • Ceto

    230 AU
  • Heliopause
  • Bowshock
    515 AU
  • Sedna
    2,000 AU
  • Oort Cloud
  • Kuiper Belt
    The Kuiper belt is a region of the Solar System beyond the planets, extending from the orbit of Neptune (at 30 AU) to approximately 50 AU from the Sun. It is similar to the asteroid belt, but it is far larger- 20 times as wide and 20 to 200 times as massive. Like the asteroid belt, it consists mainly of small bodies, or remnants from the Solar System's formation. Although many asteroids are composed primarily of rock and metal, most Kuiper belt objects are composed largely of frozen volatiles (termed "ices"), such as methane, ammonia and water. The Kuiper belt is home to three officially recognized dwarf planets: Pluto, Haumea, and Makemake. Some of the Solar System's moons, such as Neptune's Triton and Saturn's Phoebe, are also believed to have originated in the region.

    The main body of the belt is generally accepted to extend from the 2:3 resonance [with Neptune] at 39.5 AU to the 1:2 resonance at roughly 48 AU. The Kuiper belt is quite thick, with the main concentration extending as much as ten degrees outside the ecliptic plane and a more diffuse distribution of objects extending several times farther. Overall it more resembles a torus or doughnut than a belt.

    The presence of Neptune has a profound effect on the Kuiper belt's structure due to orbital resonances. Over a timescale comparable to the age of the Solar System, Neptune's gravity destabilises the orbits of any objects that happen to lie in certain regions, and either sends them into the inner Solar System or out into the scattered disc or interstellar space. This causes the Kuiper belt to possess pronounced gaps in its current layout, similar to the Kirkwood gaps in the asteroid belt.


    1993 RP

    A TNO of the plutino class. Very little is known about the object.

    42355 Typhon

    Typhon is the first known binary centaur, using an extended definition of a centaur as an object on a non-resonant (unstable) orbit with the perihelion inside the orbit of Neptune.

    1993 RO

    The first plutino discovered after Pluto itself. Very little is known about 1993 RO.

    (15788) 1993 SB

    A plutino class TNO. Very little is known about the object.

    Rhadamanthus

    A TNO. It was originally thought to be a plutino but no longer is.

    Orcus
    A likely dwarf planet. Orcus is a plutino, locked in a 2:3 resonance with Neptune, making two revolutions around the Sun to every three of Neptune's. This is much like Pluto, except that it is constrained to always be in the opposite phase of its orbit from Pluto. Moreover, the aphelion of Orcus's orbit points in nearly the opposite direction from Pluto's, although the eccentricities and inclinations are similar. Because of these similarities and contrasts, along with its large moon Vanth that recalls Pluto's large moon Charon, Orcus has been regarded as the anti-Pluto.

    The surface of Orcus is grey in color and water-rich. The ice is predominantly in crystalline form, which may be related to past cryovolcanic activity. Models of internal heating via radioactive decay suggest that Orcus may be capable of sustaining an internal ocean of liquid water.


    1994 JR1

    A minor planet that moves around the Sun in an orbit entirely located beyond Neptune. It is the first object that was confirmed to be a quasi-satellite of Pluto. It is currently following a quasi-satellite loop around Pluto. The quasi-satellite state is mainly the result of resonances with Neptune not caused by a discrete close encounter with another body. This dynamical behavior is recurrent: the object becomes a Plutonian quasi-satellite every 2 Myr and remains in that phase for nearly 350,000 years.

    1994 JR1 is moving in a very stable orbit, likely as stable as Pluto's. This suggests that it may be a primordial plutino formed around the same time Pluto itself and Charon came into existence. It is unlikely to be relatively recent debris originated in collisions within Pluto's system or a captured object.


    1999 TC36

    A triple system consisting of a central primary, which is itself a binary, and a small moon (component B). The primary is probably a rubble pile. 1999 TC36 has a very red spectral slope in visible light and a flat spectrum in near infrared. There is also probably caused by water ice.

    2003 VS2
    A TNO like Pluto, in a 2:3 orbital resonance with Neptune. A highly likely dwarf planet. It has a rotation period likely of 7.41 h. 2003 VS2 has a moderately red surface.

    Pluto
    It is the largest and second-most-massive known dwarf planet in the Solar System, and the ninth-largest and tenth-most-massive known object directly orbiting the Sun. It is the largest known trans-Neptunian object by volume but is less massive than Eris, a dwarf planet in the scattered disc. Like other Kuiper belt objects, Pluto is primarily made of ice and rock and is relatively small - about one-sixth the mass of the Moon and one-third its volume. It has a moderately eccentric and inclined orbit during which it ranges from 30 to 49 AU. This means that Pluto periodically comes closer to the Sun than Neptune, but a stable orbital resonance with Neptune prevents them from colliding. Light from the Sun takes about 5.5 hours to reach Pluto at its average distance (39.4 AU). The amount of light from the Sun on Pluto is weak, analogous to twilight on Earth.

    Pluto and Charon are sometimes considered a binary system because the barycenter of their orbits does not lie within either body. The IAU has not formalized a definition for binary dwarf planets, and Charon is officially classified as a moon of Pluto.

    Pluto's rotation period, its day, is equal to 6.39 Earth days. Like Uranus, Pluto rotates on its "side" on its orbital plane, with an axial tilt of 120°, and so its seasonal variation is extreme - at its solstices, one-fourth of its surface is in continuous daylight, whereas another fourth is in continuous darkness.

    Pluto's surface is composed of more than 98% nitrogen ice, with traces of methane and carbon monoxide. The face of Pluto oriented toward Charon contains more methane ice, whereas the opposite face contains more nitrogen and carbon monoxide ice. Pluto's surface is quite varied, with large differences in both brightness and color. Pluto is one of the most contrastive bodies in the Solar System, with as much contrast as Saturn's moon Iapetus. The color varies between charcoal black, dark orange and white. Pluto's color is more similar to that of Io, with slightly more orange, and significantly less red than Mars. Notable geographical features include Tombaugh Regio, or the "Heart" (a large bright area on the side opposite Charon), Cthulhu Regio, or the "Whale" (a large dark area on the trailing hemisphere), and the "Brass Knuckles" (a series of equatorial dark areas on the leading hemisphere).

    Pluto has a thin atmosphere consisting of nitrogen, methane, and carbon monoxide, which are in equilibrium with their ices on Pluto's surface. The surface pressure is roughly one million to 100,000 times less than Earth's atmospheric pressure. Pluto's elliptical orbit is predicted to have a major effect on its atmosphere: as Pluto moves away from the Sun, its atmosphere should gradually freeze out. When Pluto is closer to the Sun, the temperature of Pluto's solid surface increases, causing the ices to sublimate. Just like sweat cools the body as it evaporates from the skin, this sublimation cools the surface of Pluto.[123]

    Ruins of South Ataria Island
    When the SDF-1 undertook the emergency fold at the start of SWI, it took South Ataria Island and a large amount of the surrounding Pacific waters with it, depositing them 'near Pluto.'

    Presently (as of 2050-2060), it is slowly spreading over a larger area due to events that occured immediately after its arrival and subsequent interactions with gravity fields and the Solar Wind. The area looks more like an icey 'smudge' (perhaps occasionally being mistaken for a comet) in space.

    2003 AZ84
    A plutino in a 2:3 resonance with Neptune. Its light-curve amplitude deviates little from that of an ellipsoid, which suggests that it is likely one with small albedo spots. It is very probably a dwarf planet.

    The spectra and colors of 2003 AZ84 are very similar to those of Orcus. Both bodies have a flat featureless spectrum in the visible and moderately strong water ice absorption bands in the near-infrared, although 2003 AZ84 has a lower albedo.

    Ixion
    A plutino in a 2:3 resonance with Neptune. It is very likely to be a dwarf planet. Light-curve-amplitude analysis shows only small deviations, which suggests that Ixion is a spheroid with small albedo spots. It is moderately red in visible light and has a surface made of a mixture of tholin and water ice.

    Ixion's surface is a mixture of water ice, dark carbon and tholin, which is a heteropolymer formed by irradiation of clathrates of water and organic compounds. It is possible that Ixion could develop a coma or temporary atmosphere when it is closer to perihelion.

    Huya
    A plutino, in a 2:3 mean-motion resonance with Neptune. It is possibly a dwarf planet. Light-curve-amplitude analysis, which shows only small deviations, suggests that it is likely a spheroid with small albedo spots. Huya has a moderately red-sloped reflectance spectrum in the visible and near-infrared, suggesting a surface rich in organic material such as tholins.

    2005 RN43
    A highly likely dwarf planet. It is unknown how it obtained its moderate inclination of 19.3°.


    1995 SM55

    Based on a common pattern of IR water-ice absorption and the clustering of their orbital elements, it appears to be a collisional fragments broken off the dwarf planet Haumea.

    2002 MS4
    The second-largest known object in the Solar System without a name, after 2007 OR10. It is nearly certain to be a dwarf planet.

    Salacia
    A large planetoid of the Kuiper belt. A highly likely dwarf planet. Its near infrared spectrum is basically featureless and shows less than 5% water ice. Salacia has the lowest albedo and density known of any TNO that big.[6]

    2004 GV9
    It is very likely a dwarf planet. Light-curve-amplitude analysis shows only small deviations, suggesting that 2004 GV9 could be a spheroid with small albedo spots.


    2005 TN74

    It was initially suspected of being a Neptune trojan.

    2002 UX25
    A highly likely dwarf planet. A variability of the visual brightness was detected which could be fit to a period of 14.38 or 16.78 h. It is redder than Varuna, unlike its neutral-colored "twin" 2002 TX300, in spite of similar brightness and orbit elements.

    2002 UX25 is one of the largest known solid objects in the Solar System that is less dense than water. Why this should be is not well understood: objects of its size in the Kuiper belt are typically rocky and dense, and to have a similar composition to others of its kind, it would have to be exceptionally porous, which is unlikely given the compactability of water ice.


    (145453) 2005 RR43

    Based on a common pattern of IR water-ice absorption and the clustering of their orbital elements, it appears to be a collisional fragments broken off the dwarf planet Haumea.

    Varuna
    Probably a dwarf planet. Varuna is classified as a classical TNO and follows a near-circular orbit.

    Varuna has a rotational period of approximately 6.34 hours. It has a double-peaked light curve. Given the rapid rotation, rare for objects so large, Varuna is thought to be an elongated spheroid (ratio of axis 2:3)

    The surface of Varuna is moderately red (similar to Quaoar) and small amounts of water ice have been detected on its surface. The most probable composition for the surface of Varuna is a mixture of amorphous silicates (25%), complex organics (35%), amorphous carbon (15%) and water ice (25%). However, they also discuss another possible surface composition containing up to a 10% of methane ice. For an object with the characteristics of Varuna, this volatile could not be primordial, so an event, such as an energetic impact, would be needed to explain its presence on the surface.

    Haumea
    Although its shape has not been directly observed, calculations from its light curve suggest it is an ellipsoid, with its major axis twice as long as its minor. This elongation, along with its unusually rapid rotation, high density, and high albedo (from a surface of crystalline water ice), are thought to be the results of a giant collision, which left Haumea the largest member of a collisional family that includes several large trans-Neptunian objects (TNOs) and its two known moons, Hi'iaka and Namaka. Its extreme elongation makes it unique among known dwarf planets.

    Haumea's orbit has a slightly greater eccentricity than the other members of its collisional family. This is thought to be due to Haumea's weak 7:12 orbital resonance with Neptune gradually modifying its initial orbit over the course of a billion years, through the Kozai effect, which allows the exchange of an orbit's inclination for increased eccentricity.

    Haumea displays large fluctuations in brightness over a period of 3.9 hours, which can only be explained by a rotational period of this length. This is faster than any other known equilibrium body in the Solar System, and indeed faster than any other known body larger than 100 km in diameter. This rapid rotation is thought to have been caused by the impact that created its satellites and collisional family.

    Haumea is the largest member of its collisional family, a group of astronomical objects with similar physical and orbital characteristics thought to have formed when a larger progenitor was shattered by an impact. A proposal suggests that the material ejected in the initial collision instead coalesced into a large moon of Haumea, which was later shattered in a second collision, dispersing its shards outwards.


    (19308) 1996 TO66

    Based on a common pattern of IR water-ice absorption and the clustering of their orbital elements, it appears to be a collisional fragments broken off the dwarf planet Haumea.

    (120178) 2003 OP32

    Based on a common pattern of IR water-ice absorption and the clustering of their orbital elements, it appears to be a collisional fragments broken off the dwarf planet Haumea.

    Quaoar
    A probable dwarf planet, with suggestions of an elongated shape. Light-curve-amplitude analysis shows only small deviations, suggesting that Quaoar is indeed a spheroid with small albedo spots.

    At 43 AU and a near-circular orbit, Quaoar is not significantly perturbed by Neptune, unlike Pluto, which is in 2:3 orbital resonance with Neptune. Pluto is closer to the Sun than Quaoar at some times of its orbit, and farther at others.

    The surface is moderately red. Larger KBOs are often much brighter because they are covered in more fresh ice. A model of internal heating via radioactive decay suggested that, unlike Orcus, Quaoar may not be capable of sustaining an internal ocean of liquid water at the mantle-core boundary.

    2002 TX300
    A bright Kuiper belt object. A possible dwarf planet. It is a large member of the Haumea family.

    A variability of the visual brightness was also detected which could fit to 7.9 h or 15.8 h rotational period. The changes in brightness are quite close to the error margin and could also be due to an irregular shape.

    Mineralogical analysis indicates a substantial fraction of large ice (H2O) particles. The signal-to-noise ratio of the observations was insufficient to differentiate between amorphous or crystalline ice (crystalline ice was reported on Charon, Quaoar and Haumea). The proportion of highly processed organic materials (tholins), typically present on numerous trans-Neptunian objects, is very low. This lack of irradiated mantle suggest either a recent collision or comet activity.

    2005 UQ513
    A cubewano. A highly likely dwarf planet. 2005 UQ513 shows signs of weak water ice. Like Quaoar, it has a very red spectrum, which indicates that its surface probably contains a lot of complex, processed organic molecules.


    (15760) 1992 QB1

    The first trans-Neptunian object to be discovered after Pluto and Charon. It is a classical Kuiper belt object and gave rise to the name cubewano for this kind of object, after the "QB1" portion of its designation.

    It has received the number 15760 and remains unnamed; it is normally referred to simply as "QB1", even though this is technically ambiguous without the year of discovery.


    79360 Sila-Nunam

    A dynamically cold, double classical Kuiper belt object (cubewano) with components of almost equal size. It orbits very close to 4:7 mean-motion resonance with Neptune.

    Sila-Nunam is very red in visible light and has a flat featureless spectrum in the near-infrared. There are no water ice absorption bands in its near-infrared spectrum, which resembles that of Ixion. Each has apparently been resurfaced with ejecta from impacts on the other.


    53311 Deucalion

    A Trans Neptunian Object.

    1998 WW31

    A double Kuiper belt object. It forms a binary system with another object with the provisional designation S/2000 (1998 WW31) 1: one of the most symmetrical binaries known in the Solar System.

    The two bodies are very close in size, with a diameter ratio of 1.2 and a mass ratio of 1.74, assuming similar surfaces and densities. Their combined mass is 1/6000th that of the Pluto-Charon system.

    2010 KZ39
    A highly likely dwarf planet.


    2008 KV42 "Drac"

    A trans-Neptunian object (TNO) with a retrograde orbit. Its 104degree inclination and its retrograde motion suggest that it is the missing link between its source in the inner Oort cloud and Halley-type comets.

    Its unusual orbit suggests that 2008 KV42 may have been perturbed inwards from its source, most likely in the inner Oort cloud, by an unknown gravitational disturbance. Its discovery may reveal the source regions for Halley-type comets which also have an retrograde orbit, but their origin remains unknown. 2008 KV42 itself is believed to be in an intermediate stage towards becoming a comet.

    Chaos
    A Kuiper-belt object not in resonance with any planet. It is a likely dwarf planet.

    Makemake
    A dwarf planet and perhaps the largest Kuiper belt object (KBO) in the classical population, with a diameter that is about 2/3 the size of Pluto. Makemake has no known satellites, which makes it unique among the largest KBOs. Its extremely low average temperature, about 30 K means its surface is covered with methane, ethane, and possibly nitrogen ices.

    Makemake's orbit lies far enough from Neptune to remain stable over the age of the Solar System. Makemake, however, is a member of the "dynamically hot" class of classical KBOs, meaning that it has a high inclination compared to others in its population. Makemake is, probably coincidentally, near the 11:6 resonance with Neptune.

    The surface of Makemake resembles that of Pluto. Like Pluto, Makemake appears red in the visible spectrum, and significantly redder than the surface of Eris. Spectral analysis of Makemake's surface revealed that methane must be present in the form of large grains at least one centimetre in size. In addition, large amounts of ethane and tholins may be present as well. The tholins are probably responsible for the red color of the visible spectrum. Although evidence exists for the presence of nitrogen ice on its surface, at least mixed with other ices, there is nowhere near the same level of nitrogen as on Pluto and Triton. The relative lack of nitrogen ice suggests that its supply of nitrogen has somehow been depleted over the age of the Solar System.

    The surface of Makemake is not homogeneous. Although the majority of it is covered by nitrogen and methane ices, there are small patches of dark terrain that make up 3-7% of the surface.

    Makemake presently lacks a substantial atmosphere. The presence of methane and possibly nitrogen suggests that Makemake could have a transient atmosphere similar to that of Pluto near its perihelion.

    Varda
    Highly likely to be a dwarf planet.

    2010 RF43
    A highly likely dwarf planet.


    (230965) 2004 XA192

    2002 AW197
    A classical Kuiper belt object (cubewano). A probable dwarf planet.

    Light-curve-amplitude analysis shows only small deviations, which suggests that it is a spheroid with small albedo spots. Analysis of spectra reveals a strong red slope and no presence of water ice, suggesting organic material.

    2007 JJ43
    A highly likely dwarf planet. One of the twenty brightest exhibited by TNOs. Observations suggest that it does not have a companion.


    (120132) 2003 FY128

    2003 QX113
    It may be a dwarf planet.

    2001 UR163
    A likely dwarf planet that resides in the scattered disc. Light-curve-amplitude analysis shows only small deviations, suggesting that 2001 UR163 is a spheroid with small albedo spots.

    It has the reddest color index of any object in the Solar System. In the visible spectrum, 2001 UR163 would appear orange-brown, depending on its albedo.


    (48639) 1995 TL8

    It possesses a relatively large satellite.

    "Kuiper gap" or "Kuiper cliff"
    The 1:2 resonance with Neptune appears to be an edge beyond which few objects are known. It is not clear whether it is actually the outer edge of the classical belt, or just the beginning of a broad gap. Objects have been detected at the 2:5 resonance at roughly 55 AU, well outside the classical belt; however, predictions of a large number of bodies in classical orbits between these resonances have not been verified through observation.

    Based on estimations of the primordial mass required to form Uranus and Neptune, as well as bodies as large as Pluto, earlier models of the Kuiper belt had suggested that the number of large objects would increase by a factor of two beyond 50 AU, so this sudden drastic falloff, known as the "Kuiper cliff", was completely unexpected, and its cause, to date, is unknown. Possible explanations include that material at that distance was too scarce or too scattered to accrete into large objects, or that subsequent processes removed or destroyed those that did. The gravitational attraction of an unseen large planetary object, perhaps the size of Earth or Mars, might be responsible.

    Scattered disc
    The scattered disc (or scattered disk) is a distant region of the Solar System that is sparsely populated by icy minor planets, a subset of the broader family of TNOs. The scattered-disc objects (SDOs) have orbital eccentricities ranging as high as 0.8, inclinations as high as 40 degrees, and perihelia greater than 30 AU. These extreme orbits are believed to be the result of gravitational "scattering" by the gas giants, and the objects continue to be subject to perturbation by the planet Neptune.

    Although the closest scattered-disc objects approach the Sun at about 30-35 AU, their orbits can extend well beyond 100 AU. This makes scattered objects among the most distant and coldest objects in the Solar System. The innermost portion of the scattered disc overlaps with a torus-shaped region of orbiting objects traditionally called the Kuiper belt, but its outer limits reach much farther away from the Sun and farther above and below the ecliptic than the Kuiper belt proper.

    Because of its unstable nature, astronomers now consider the scattered disc to be the place of origin for most periodic comets in the Solar System, with the centaurs, a population of icy bodies between Jupiter and Neptune, being the intermediate stage in an object's migration from the disc to the inner Solar System. Eventually, perturbations from the giant planets send such objects towards the Sun, transforming them into periodic comets. Many Oort cloud objects are also believed to have originated in the scattered disc.

    2002 TC302
    A red, 2:5 resonant TNO. The red spectra suggests that 2002 TC302 has very little fresh ice on its surface. Its rotational period is most likely 5.41 h.


    (26375) 1999 DE9

    Light-curve-amplitude analysis shows only small deviations, suggesting it is a spheroid with small albedo spots. It is in 2:5 resonance with Neptune. Spectral analysis has shown traces of ice.

    2000 YW134

    A binary trans-Neptunian object (TNO) that is likely in 3:8 resonance with Neptune. In the visible part of the spectrum, the surface of 2000 YW134 is moderately red. It is a possible dwarf planet.

    2004 XR190 "Buffy"
    Considered a detached object, it is particularly unusual for two reasons. With an inclination of 47 degrees, it is the largest possible dwarf planet that has an inclination larger than 45 degrees, traveling further "up and down" than "left to right" around the Sun when viewed edge-on along the ecliptic. Second, it has an unusually circular orbit for a scattered-disc object (SDO). Although it is thought that traditional scattered-disc objects have been ejected into their current orbits by gravitational interactions with Neptune, the low eccentricity of its orbit and the distance of its perihelion seems hard to reconcile with such celestial mechanics. This has led to some uncertainty as to the current theoretical understanding of the outer Solar System. The theories include close stellar passages, rogue planets/planetary embryos in the early Kuiper belt, and resonance interaction with an outward-migrating Neptune.

    2007 OR10

    A very large planetoid located in the scattered disc. It is the largest known body in the Solar System without a name. It is approximately the size of Haumea, and appears to be a dwarf planet. It is in a 3:10 resonance with Neptune.

    The spectrum of 2007 OR10 shows signatures for both water ice and methane, which makes it similar in composition to Quaoar. The presence of red methane frost on the surfaces of both 2007 OR10 and Quaoar implies the existence of a tenuous methane atmosphere on both objects, slowly evaporating into space. Although 2007 OR10 comes closer to the Sun than Quaoar, and is thus warm enough that a methane atmosphere should evaporate, its larger mass makes retention of an atmosphere just possible.

    The presence of water ice on the surface of 2007 OR10 implies a brief period of cryovolcanism in its distant past.

    2006 QH181
    Very likely a dwarf planet. It currently has a too poorly determined orbit to know whether there is a resonance with Neptune.

    Eris
    Eris is the most massive known dwarf planet in the Solar System and the ninth most massive body known to orbit the Sun directly. It is 27% more massive than Pluto, or about 0.27% of the Earth's mass.

    Infrared light from the object revealed the presence of methane ice, indicating that the surface may be similar to that of Pluto, which at the time was the only TNO known to have surface methane, and of Neptune's moon Triton, which also has methane on its surface. Due to Eris's distant eccentric orbit, Eridian surface temperature is estimated to vary between about 30 and 56 kelvin

    Unlike the somewhat reddish Pluto and Triton, however, Eris appears almost grey. It is far enough away from the Sun that methane can condense onto its surface even where the albedo is low. The condensation of methane uniformly over the surface reduces any albedo contrasts and would cover up any deposits of red tholins. Even though Eris can be up to three times further from the Sun than Pluto, it approaches close enough that some of the ices on the surface might warm enough to sublime.

    As methane is highly volatile, its presence shows either that Eris has always resided in the distant reaches of the Solar System where it is cold enough for methane ice to persist, or that the celestial body has an internal source of methane to replenish gas that escapes from its atmosphere. This contrasts with observations of another discovered TNO, Haumea, which reveal the presence of water ice but not methane.

    2010 EK139
    Very likely a dwarf planet. The object is in a 7:2 resonance with Neptune. Observations suggest that there isn't a satellite.

    2007 UK126
    A probable dwarf planet. Its orbital eccentricity suggests that it was gravitationally scattered onto its eccentric orbit.


    (145480) 2005 TB190

    A likely dwarf planet. In the visible light, 2005 TB190 has a moderately red spectral slope. It was found to have a rotation period of 12.68+/-3 hours, a common value for TNOs of its size.

    2010 RE64
    A scattered disc object that is highly likely to be a dwarf planet.

    1996 TL66
    Light-curve-amplitude analysis shows only small deviations, suggesting 1996 TL66 is a spheroid with small albedo spots and may be a dwarf planet.

    Termination shock
    The termination shock is the point in the heliosphere where the solar wind slows down to subsonic speed (relative to the Sun) because of interactions with the local interstellar medium. This causes compression, heating, and a change in the magnetic field. In the Solar System the termination shock is believed to be 75 to 90 AU from the Sun.

    The shock arises because solar wind particles are emitted from the Sun at about 400 km/s, while the speed of sound (in the interstellar medium) is about 100 km/s (the exact speed depends on the density, which fluctuates considerably). The interstellar medium, although very low in density, nonetheless has a constant pressure associated with it; the pressure from the solar wind decreases with the square of the distance from the Sun. As one moves far enough away from the Sun, the pressure from the interstellar medium becomes sufficient to slow the solar wind down to below its speed of sound; this causes a shock wave.

    The heliosphere may be irregularly shaped, bulging outwards in the Sun's northern hemisphere and pushed inward in the south.

    Heliosheath
    The heliosheath is the region of the heliosphere beyond the termination shock. Here the solar wind is slowed, compressed and made turbulent by its interaction with the interstellar medium. Its distance from the Sun is approximately 80 to 100 AU at its closest point.

    The Voyager 1 and Voyager 2 spacecraft are currently studying the heliosheath. In late 2010, Voyager 1 reached a region of the heliosheath where the solar wind's velocity had dropped to zero.[ In 2011, astronomers announced that the Voyagers had determined that the heliosheath is not smooth, but is filled with 100 million-mile-wide bubbles created by the impact of the solar wind and the interstellar medium. The probably sausage-shaped bubbles are formed by magnetic reconnection between oppositely oriented sectors of the solar magnetic field as the solar wind slows down. They probably represent self-contained structures that have detached from the interplanetary magnetic field.

    Ceto
    Ceto is a close binary TNO in which the components are of similar size. It has been suggested that tidal forces, together with other potential heat sources might have raised the temperature sufficiently to crystallise amorphous ice and reduce the void space inside the object. The same tidal forces could be responsible for the quasi-circular orbits of the components of Ceto.


    2000 CR105

    A possible dwarf planet that orbits the Sun in a highly eccentric orbit. The albedo is expected to be low because the object has a blue (neutral) color. However, if the albedo is higher, the object could easily be half that size.
    2000 CR105 and Sedna differ from scattered-disc objects in that they are not within the gravitational influence of the planet Neptune even at their perihelion distances (closest approaches to the Sun). It is something of a mystery as to how these objects came to be in their current, far-flung orbits.

    Heliopause
    The heliopause is the theoretical boundary where the Sun's solar wind is stopped by the Interstellar medium; where the solar wind's strength is no longer great enough to push back the stellar winds of the surrounding stars. This is the boundary where the interstellar medium and solar wind pressures balance.

    The crossing of the heliopause should be signaled by a sharp drop in the temperature of charged particles, a change in the direction of the magnetic field, and an increase in the amount of galactic cosmic rays.

    In the fall of 2013, NASA announced that Voyager 1 had crossed the heliopause as of August 25, 2012. This was at a distance of 121 AU from the Sun. Contrary to predictions, data from Voyager 1 indicates the magnetic field of the galaxy is aligned with the solar magnetic field.


    Heliotail

    The heliotail is the solar system's tail or can be understood as the tail of the heliosphere. Similarly it can be compared to a comet, which also has a tail (however a comet's tail does not stretch behind it as it moves, it is always pointing away from the Sun). A further explanation of the tail is a region where the Sun's Solar Wind flows down and ultimately escapes the heliosphere, slowly evaporating because of charge exchange.

    The shape of this newly found tail by NASA's Interstellar Boundary Explorer (IBEX) is that of a four-leaf clover. Due to the particles in the tail, they do not shine, therefore it cannot be seen with conventional instruments. IBEX has made the first observations by using a technique called "energetic neutral atom energy" which is the process of measuring the neutral particles created by collisions at the solar system's boundaries.

    The tail has shown to obtain fast and slow particles; the slow particles are on the side and the fast particles are encompassed in the center. The shape of the tail can be linked to the sun sending out fast solar winds near its poles and slow solar wind near its equator more recently. The clover-shaped tail moves further away from the sun, which makes the charged particles begin to morph into a new orientation.

    Bowshock
    It was long hypothesized that the Sun produces a "shock wave" in its travels within the interstellar medium. It would occur if the interstellar medium is moving supersonically "toward" the Sun, since its solar wind moves "away" from the sun supersonically. When the interstellar wind hits the heliosphere it slows and creates a region of turbulence. A bow shock was thought to possibly occur at about 230 AU, but in 2012 it was determined it probably does not exist. This conclusion resulted from new measurements: The velocity of the LISM (Local Interstellar Medium) relative to the Sun's was measured it at 23.2 km/s.

    This phenomenon has been observed outside our solar system, around stars other than the Sun. The red giant star Mira in the constellation Cetus has been shown to have both a debris tail of ejecta from the star and a distinct shock in the direction of its movement through space (at over 130 km/s).


    2004 VN112

    Its large eccentricity strongly suggests that it was gravitationally scattered onto its current orbit. Because it is, like all detached objects, outside of the current influence of Neptune, how it came to have this orbit cannot yet be explained.
    A possible dwarf planet. The albedo is expected to be low because the object has a blue (neutral) color. However, if the albedo is higher, the object could easily be half that size.

    2007 TG422

    A possible dwarf planet. The albedo is expected to be low because the object has a blue (neutral) color. But if the albedo is higher, the object could easily be much smaller.

    2000 OO67

    It is remarkable for its highly eccentric orbit. With a perihelion of 21 AU, almost crossing the orbit of Uranus; some astronomers list it as a centaur.
    90377 Sedna
    Its surface composition is similar to that of some other trans-Neptunian objects, being largely a mixture of water, methane and nitrogen ices with tholins. Its surface is one of the reddest in the Solar System. Sedna's exceptionally long and elongated orbit has led to much speculation as to its origin. It may be the first known member of the inner Oort cloud. Others speculate that it might have been tugged into its current orbit by a passing star, perhaps one within the Sun's birth cluster, or even that it was captured from another star system. Another hypothesis suggests that its orbit may be evidence for a large planet beyond the orbit of Neptune.

    Measurements suggest a rotational period of 10 hours. Sedna's dark red colour may be caused by a surface coating of hydrocarbon sludge, or tholin, formed from simpler organic compounds after long exposure to ultraviolet radiation. Its surface is homogeneous in colour and spectrum; this may be because Sedna, unlike objects nearer the Sun, is rarely impacted by other bodies, which would expose bright patches of fresh icy material like that on 8405 Asbolus. Models of internal heating via radioactive decay suggest that Sedna might be capable of supporting a subsurface ocean of liquid water.


    2006 SQ372

    It has a strongly eccentric orbit, crossing that of Neptune near perihelion but bringing it more than 1,500 AU from the Sun at aphelion. The object could possibly be a comet. The discoverers hypothesize that the object could come from the inner Oort cloud, but other scientists consider other possibilities, as "it may have formed from debris just beyond Neptune [in the Kuiper belt] and been 'kicked' into its distant orbit by a planet like Neptune or Uranus".
    Oort Cloud
    The Oort cloud (sometimes called the Opik-Oort Cloud), is a hypothesized spherical cloud of comets which may lie roughly 50,000 AU, or nearly a light-year, from the Sun. This places the cloud at nearly a quarter of the distance to Proxima Centauri, the nearest star to the Sun. The Kuiper belt and the scattered disc, the other two reservoirs of trans-Neptunian objects, are less than one thousandth of the Oort cloud's distance. The outer limit of the Oort cloud defines the cosmographical boundary of the Solar System and the region of the Sun's gravitational dominance.

    Astronomers believe that the matter composing the Oort cloud formed closer to the Sun and was scattered far out into space by the gravitational effects of the giant planets early in the Solar System's evolution. It is speculated that the Oort cloud is, at least partly, the product of an exchange of materials between the Sun and its sister stars as they formed and drifted apart. Objects in the Oort cloud are largely composed of ices, such as water, ammonia, and methane. However, the discovery of the object 1996 PW, an asteroid in an orbit more typical of a long-period comet, suggests that the cloud may also contain rocky objects.

    Although no confirmed direct observations of the Oort cloud have been made, astronomers believe that it is the source of all long-period and Halley-type comets entering the inner Solar System and many of the centaurs and Jupiter-family comets as well. The outer Oort cloud is only loosely bound to the Solar System, and thus is easily affected by the gravitational pull both of passing stars and of the Milky Way Galaxy itself. These forces occasionally dislodge comets from their orbits within the cloud and send them towards the inner Solar System. Based on their orbits, most of the short-period comets may come from the scattered disc, but some may still have originated from the Oort cloud.

    The Oort cloud is thought to be a remnant of the original protoplanetary disc that formed around the Sun approximately 4.6 billion years ago. The most widely accepted hypothesis is that the Oort cloud's objects initially coalesced much closer to the Sun as part of the same process that formed the planets and asteroids, but that gravitational interaction with young gas giant planets such as Jupiter ejected the objects into extremely long elliptic or parabolic orbits. Recent research has been cited by NASA hypothesizing that a large number of Oort cloud objects are the product of an exchange of materials between the Sun and its sibling stars as they formed and drifted apart, and it is suggested that many - possibly the majority - of Oort cloud objects were not formed in close proximity to the Sun. Simulations of the evolution of the Oort cloud from the beginnings of the Solar System to the present suggest that the cloud's mass peaked around 800 million years after formation, as the pace of accretion and collision slowed and depletion began to overtake supply.

    Models suggest that the scattered disc, which is the main source for periodic comets in the Solar System, might also be the primary source for Oort cloud objects. According to the models, about half of the objects scattered travel outward towards the Oort cloud, while a quarter are shifted inward to Jupiter's orbit, and a quarter are ejected on hyperbolic orbits. The scattered disc might still be supplying the Oort cloud with material. A third of the scattered disc's population is likely to end up in the Oort cloud after 2.5 billion years.

    Gravitational interaction with nearby stars and galactic tides modified cometary orbits to make them more circular. This explains the nearly spherical shape of the outer Oort cloud. On the other hand, the Hills cloud, which is bound more strongly to the Sun, has yet to acquire a spherical shape. Recent studies have shown that the formation of the Oort cloud is broadly compatible with the hypothesis that the Solar System formed as part of an embedded cluster of 200-400 stars. These early stars likely played a role in the cloud's formation, since the number of close stellar passages within the cluster was much higher than today, leading to far more frequent perturbations.

    It is thought that other stars are likely to possess Oort clouds of their own, and that the outer edges of two nearby stars' Oort clouds may sometimes overlap, causing the occasional intrusion of a comet into the inner solar system. The star with the greatest possibility of perturbing the Oort cloud in the next 10 million years is Gliese 710.


    REFERENCES
  • Wikipedia and the numerous contributors to it
  • The Macross Compendium's Atlas
  • The UNSDB's Colonies and Bases list by Daniel Henwood

  • © Aaron Sketchley
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