Radiation astronomy/Scattered disks
Scattered Disk Objects (up to 100 AU): Kuiper Belt objects are shown in grey, resonant objects within the Scattered Disk are shown in green.
The position of an object represents
- its orbit’s semi-major axis a in AU and the orbital period in years (horizontal axis)
- its orbit’s inclination i in degrees (vertical axis).
The size of the circle illustrates the object’s size relative to others. For a few large objects, the diameter drawn represents the best current estimates. For all others, the circles represent the absolute magnitude of the object.
The eccentricity of the orbit is shown indirectly by a segment extending from the left (perihelion) to the aphelion to the right. In other words, the segment illustrates the variations of the object's distance from the Sun. Objects with nearly circular orbits will show short segments while highly elliptical orbits will be represented by long segments.
Main resonances with Neptune are marked with vertical bars; 1:1 marks the position of Neptune’s orbit (and its Trojan asteroids), 2:3 marks the orbit of Pluto (and plutinos) etc.
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 trans-Neptunian objects. The scattered-disc objects (SDOs) have orbital eccentricities ranging as high as 0.8, inclinations as high as 40°, and perihelia greater than 30 astronomical units (4.5 x 109 km; 2.8 x 109 mi.). While the nearest distance to the Sun approached by scattered objects is about 30–35 AU, their orbits can extend well beyond 100 AU. This makes scattered objects "among the most distant and cold 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. The literature is inconsistent in the use of the phrases "scattered disc" and "Kuiper belt"; for some, they are distinct populations; for others, the scattered disc is part of the Kuiper belt and authors may even switch between these two uses in a single publication.
Periodic comets[edit | edit source]
The image at the right is an optical astronomy image of the comet 67P/Churyumov-Gerasimenko. Rosetta's OSIRIS narrow-angle camera made the image on 3 August 2014 from a distance of 285 km. The image resolution is 5.3 metres/pixel.
The left image is rotated 90° from the right. The location of the right image is the front view of the left side just out of view in the left image. The object rotates by the right hand rule from the left image to the right.
Note that due to the evaporation of volatiles, the surface of the rocky object appears pitted or cratered.
Def. a "comet which orbits the Sun and which returns to the innermost point of its orbit at known, regular intervals" is called a periodic comet. "The short period comets have orbital periods <20 years and low inclination. Their orbits are controlled by Jupiter and thus they are also called Jupiter Family comets. [...] Because the orbit crosses that of Jupiter, the comet will have gravitational interactions with this massive planet. The objects orbit will gradually change from these interactions and eventually the object will either be thrown out of the Solar System or collide with a planet or the Sun."
Perihleion distance in AU = 1.243, eccentricity = 0.641, inclination = 7.0, and orbital period in years = 2.745.
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.
Centaurs[edit | edit source]
"The recent investigation of the orbital distribution of Centaurs (Emel’yanenko et al., 2005) showed that there are two dynamically distinct classes of Centaurs, a dominant group with semimajor axes a > 60 AU and a minority group with a < 60 AU." "[T]he intrinsic number of such objects is roughly an order of magnitude greater than that for a<60 AU".
Centaurs are small Solar System bodies with a semi-major axis between those of the outer planets, generally have unstable orbits because they cross or have crossed the orbits of one or more of the giant planets; almost all their orbits have dynamic lifetimes of only a few million years. There is one centaur, 514107 Kaʻepaokaʻawela, which may be in a stable (though retrograde) orbit. Centaurs typically behave with characteristics of both asteroids and comets and are named after the mythological centaurs that were a mixture of horse and human. It has been estimated that there are around 44,000 centaurs in the Solar System with diameters larger than 1 kilometer.
No centaur has been photographed up close, although there is evidence that Saturn's moon Phoebe, imaged by the Cassini–Huygens (Cassini) probe in 2004, may be a captured centaur that originated in the Kuiper belt.
Even centaurs such as 2000 GM137 and 2001 XZ255}, which do not currently cross the orbit of any planet, are in gradually changing orbits that will be perturbed until they start to cross the orbit of one or more of the giant planets.
The Minor Planet Center (MPC) defines centaurs as having a perihelion beyond the orbit of Jupiter (q > 5.2 AU) and a semi-major axis less than that of Neptune (a < 30.1 AU).
The Jet Propulsion Laboratory (JPL) similarly defines centaurs as having a semi-major axis, a, between those of Jupiter (5.5 AU < a) and Neptune (a < 30.1 AU).
The Deep Ecliptic Survey (DES) defines centaurs using a dynamical classification scheme. These classifications are based on the simulated change in behavior of the present orbit when extended over 10 million years. The DES defines centaurs as non-resonant objects whose instantaneous (osculating) perihelia are less than the osculating semi-major axis of Neptune at any time during the simulation. This definition is intended to be synonymous with planet-crossing orbits and to suggest comparatively short lifetimes in the current orbit.
The collection The Solar System Beyond Neptune (2008) defines objects with a semi-major axis between those of Jupiter and Neptune and a Jupiter – Tisserand's parameter above 3.05 – as centaurs, classifying the objects with a Jupiter Tisserand's parameter below this and, to exclude Kuiper belt objects, an arbitrary perihelion cut-off half-way to Saturn (q < 7.35 AU) as Jupiter-family comets (This would make 60558 Echeclus (q = 5.8 AU, TJ = 3.03) and 52872 Okyrhoe (q = 5.8 AU; TJ = 2.95), which have traditionally been classified as centaurs, and 944 Hidalgo (q = 1.95 AU; TJ = 2.07), which has traditionally been considered an asteroid and is classified as a centaur by JPL, Jupiter-family comets, not centaurs.) and classifying those objects on unstable orbits with a semi-major axis larger than Neptune's as members of the scattered disc.
Centaurs are objects that are non-resonant with a perihelion inside the orbit of Neptune that can be shown to likely cross the Hill sphere of a gas giant within the next 10 million years, so that centaurs can be thought of as objects scattered inwards and that interact more strongly and scatter more quickly than typical scattered-disc objects.
The JPL Small-Body Database lists 452 centaurs. There are an additional 116 trans-Neptunian objects (objects with a semi-major axis further than Neptune's, i.e. a > 30.1 AU) with a perihelion closer than the orbit of Uranus (q < 19.2 AU).
The Committee on Small Body Nomenclature of the International Astronomical Union has adopted the following naming convention for such objects: Befitting their centaur-like transitional orbits between TNOs and comets, "objects on unstable, non-resonant, giant-planet-crossing orbits with semimajor axes greater than Neptune's" are to be named for other hybrid and shape-shifting mythical creatures. Thus far, only the binary objects 65489 Ceto and Phorcys and 42355 Typhon and Echidna have been named according to the new policy.
Centaurs with measured diameters listed as possible dwarf planets include 10199 Chariklo, (523727) 2014 NW65, 2060 Chiron, and 54598 Bienor.
The colours of centaurs are very diverse, which challenges any simple model of surface composition. In the side-diagram, the colour indices are measures of apparent magnitude of an object through blue (B), visible (V) (i.e. green-yellow) and red (R) filters. The diagram illustrates these differences (in exaggerated colours) for all centaurs with known colour indices. For reference, two moons: Triton and Phoebe, and planet Mars are plotted (yellow labels, size not to scale).
Centaurs appear to be grouped into two classes:
- very red – for example 5145 Pholus
- blue (or blue-grey, according to some authors) – for example 2060 Chiron
|55576 Amycus||2002||Near Earth Asteroid Tracking (NEAT) at Palomar Observatory||11.1 Ma||UK|
|54598 Bienor||2000||Marc W. Buie et al.||?||U|
|10370 Hylonome||1995||Mauna Kea Observatory||6.3 Ma||UN|
|10199 Chariklo||1997||Spacewatch||10.3 Ma||U|
|8405 Asbolus||1995||Spacewatch (James V. Scotti)||0.86 Ma||SN|
|7066 Nessus||1993||Spacewatch (David L. Rabinowitz)||4.9 Ma||SK|
|5145 Pholus||1992||Spacewatch (David L. Rabinowitz)||1.28 Ma||SN|
|2060 Chiron||1977||Charles T. Kowal||1.03 Ma||SU|
Trans-Neptunian objects[edit | edit source]
Over a thousand trans-Neptunian objects were detected between 1992 and 2006.
Twelve minor planets with a semi-major axis greater than 150 AU and perihelion greater than 30 AU are known, which are called extreme trans-Neptunian objects (ETNOs).
Discrepancies in the early 1900s between the observed and expected orbits of Uranus and Neptune suggested that there were one or more additional planets beyond Neptune, but revised estimates of Neptune's mass from the Voyager 2 flyby in 1989 showed that the problem was spurious.
While the relatively dimmer bodies, as well as the population as the whole, are reddish (V−I = 0.3–0.6), the bigger objects are often more neutral in colour (infrared index V−I < 0.2). This distinction leads to suggestion that the surface of the largest bodies is covered with ices, hiding the redder, darker areas underneath.
|Color||Plutinos||Cubewanos||Centaurs||Scattered disc object (SDOs)||Comets||Jupiter trojans|
Pluto[edit | edit source]
Pluto is the second largest dwarf planet known (after Eris].
In the image on the right are shown from left to right: Pluto, Charon, Nix and Hydra.
The observations on the left by Hubble were made with the European Space Agency's Faint Object Camera.
Pluto is a very peculiar object. Its orbit is tilted and is more elliptical than the orbits of any of the other planets in the solar system. Pluto also rotates upside down with its North Pole below the plane of the solar system in the opposite sense of the Earth and most of the other planets. Pluto is smaller than our own Moon and also denser than any of its neighbors in the outer solar system.
Pluto is currently near its closest approach to the Earth in its 249 year journey around the Sun, and is approximately four and a half billion kilometers away. The bright object at the center of the frame is Pluto while Charon is the fainter object in the lower left. Charon is fainter than Pluto because it is smaller and, probably, because its surface is covered by water ice whereas Pluto is thought to be covered mainly by the more reflective methane frost or snow. As indicated in the diagram at the bottom of the photograph, Charon's orbit around Pluto is a circle seen nearly edge on from Earth, with a radius of almost twenty thousand kilometers - a distance equal to approximately one and a half times the diameter of the Earth. At the time of observation, Charon was near its maximum apparent distance from Pluto, so that its angular separation was about nine tenths of an arcsecond. Because of the peculiar orientation of the Pluto-Charon orbit with respect to our line of sight, Charon approaches to within less than one tenth of an arcsecond of Pluto every three days.
"Over the weekend, scientists discovered that it is a bit bigger than they expected. Previous estimates had put it somewhere between 715 and 746 miles, but new information suggests Pluto's radius is about 736 miles across, putting it solidly at the upper end of the estimate."
"At heights of about 11,000 feet, the Norgay Montes [on the right] most closely approximates the height of the Rockies."
"NASA scientists identified this newfound range of water-ice mountains [on the left] based on high-res images obtained by the New Horizons spacecraft."
"The mountain range is located in the dwarf planet's heart-shaped feature, called Tombaugh Regio after Pluto's discoverer, Clyde Tombaugh. The mountains rise to about the height of the Appalachian Mountains on Earth, which reach a maximum height of about 6,000 feet."
In the latest data from NASA's New Horizons spacecraft, a new close-up image of Pluto reveals a vast, craterless plain that appears to be no more than 100 million years old, and is possibly still being shaped by geologic processes. This frozen region is north of Pluto's icy mountains, in the center-left of the heart feature, informally named "Tombaugh Regio" (Tombaugh Region).
This fascinating icy plains region -- resembling frozen mud cracks on Earth -- has been informally named "Sputnik Planum" (Sputnik Plain) after the Earth's first artificial satellite. It has a broken surface of irregularly-shaped segments, roughly 12 miles (20 kilometers) across, bordered by what appear to be shallow troughs. Some of these troughs have darker material within them, while others are traced by clumps of hills that appear to rise above the surrounding terrain. Elsewhere, the surface appears to be etched by fields of small pits that may have formed by a process called sublimation, in which ice turns directly from solid to gas, just as dry ice does on Earth.
The irregular shapes may be the result of the contraction of surface materials, similar to what happens when mud dries. Alternatively, they may be a product of convection, similar to wax rising in a lava lamp. On Pluto, convection would occur within a surface layer of frozen carbon monoxide, methane and nitrogen, driven by the scant warmth of Pluto's interior.
Pluto's icy plains also display dark streaks that are a few miles long. These streaks appear to be aligned in the same direction and may have been produced by winds blowing across the frozen surface.
The names, listed below, pay homage to the underworld mythology, pioneering space missions, historic pioneers who crossed new horizons in exploration, and scientists and engineers associated with Pluto and the Kuiper Belt.
- Tombaugh Regio honors Clyde Tombaugh (1906–1997), the U.S. astronomer who discovered Pluto in 1930 from Lowell Observatory in Arizona.
- Burney crater honors Venetia Burney (1918–2009), who as an 11-year-old schoolgirl suggested the name "Pluto" for Clyde Tombaugh's newly discovered planet. Later in life she taught mathematics and economics.
- Sputnik Planitia is a large plain named for Sputnik 1, the first space satellite, launched by the Soviet Union in 1957.
- Tenzing Montes and Hillary Montes are mountain ranges honoring Tenzing Norgay (1914–1986) and Sir Edmund Hillary (1919–2008), the Indian/Nepali Sherpa and New Zealand mountaineer were the first to reach the summit of Mount Everest and return safely.
- Al-Idrisi Montes honors Ash-Sharif al-Idrisi (1100–1165/66), a noted Arab mapmaker and geographer whose landmark work of medieval geography is sometimes translated as "The Pleasure of Him Who Longs to Cross the Horizons."
- Djanggawul Fossae defines a network of long, narrow depressions named for the Djanggawuls, three ancestral beings in indigenous Australian mythology who traveled between the island of the dead and Australia, creating the landscape and filling it with vegetation.
- Sleipnir Fossa is named for the powerful, eight-legged horse of Norse mythology that carried the god Odin into the underworld.
- Virgil Fossae honors Virgil, one of the greatest Roman poets and Dante's fictional guide through hell and purgatory in the Divine Comedy.
- Adlivun Cavus is a deep depression named for Adlivun, the underworld in Inuit mythology.
- Hayabusa Terra is a large land mass saluting the Japanese spacecraft and mission (2003–2010) that performed the first asteroid sample return.
- Voyager Terra honors the pair of NASA spacecraft, launched in 1977, that performed the first "grand tour" of all four giant planets. The Voyager spacecraft are now probing the boundary between the Sun and interstellar space.
- Tartarus Dorsa is a ridge named for Tartarus, the deepest, darkest pit of the underworld in Greek mythology.
- Elliot crater recognizes James Elliot (1943–2011), an MIT researcher who pioneered the use of stellar occultations to study the solar system – leading to discoveries such as the rings of Uranus and the first detection of Pluto's thin atmosphere.
Charon[edit | edit source]
On 22 June 1978, an astronomer at the U.S. Naval Observatory in Washington, D.C. was making routine measurements of photographic plates taken with the 1.55-meter (61-inch) Kaj Strand Astrometric Reflector at the USNO Flagstaff Station in Arizona. The purpose of these images was to refine the orbit of the far-flung planet Pluto to help compute a better ephemeris for this distant object.
Astronomer James W. Christy had noticed that a number of the images of Pluto appeared elongated, but images of background stars on the same plate did not. Other plates showed the planet as a tiny, round dot. Christy examined a number of Pluto images from the USNO archives, and he noticed the elongations again. Furthermore, the elongations appeared to change position with respect to the stars over time. After eliminating the possibility that the elongations were produced by plate defects and background stars, the only plausible explanation was that they were caused by a previously unknown moon orbiting Pluto at a distance of about 19,600 kilometers (12,100 miles) with a period of just over six days.
On 7 July 1978, the discovery was formally announced to the astronomical community and the world by the IAU Central Bureau for Astronomical Telegrams via IAU Circular 3241. The discovery received the provisional designation "1978 P 1"; Christy proposed the name "Charon", after the mythological ferryman who carried souls across the river Acheron, one of the five mythical rivers that surrounded Pluto's underworld.
Over the course of the next several years, another USNO astronomer, the late Robert S. Harrington, calculated that Pluto and its newly-found moon would undergo a series of mutual eclipses and occultations, beginning in early 1985. On 17 February 1985 the first successful observation of one of these transits was made at with the 0.9-meter (36-inch) reflector at the University of Texas McDonald Observatory, within 40 minutes of Harrington's predicted time. The IAU Circular announcing these confirming observations was issued on 22 February 1985. With this confirmation, the new moon was officially named Charon.
Pluto was discovered at Lowell Observatory in 1930 by the late Clyde W. Tombaugh, an amateur astronomer from Kansas who was hired by the Observatory specifically to photograph the sky with a special camera and search for the planet predicted by the Observatory's founder, Percival Lowell.
Lowell had deduced the existence of a "Planet X" by studying small anomalies in the orbits of Uranus and Neptune. As it turned out, Pluto's discovery was almost entirely serendipitous; Pluto's tiny mass was far too small to account for the anomalies, which were resolved when Voyager 2 determined more precise masses for Uranus and Neptune.
The discovery of Charon has led to a much better understanding of just how tiny Pluto is. Its diameter is about 2274 km (1413 miles), and its mass is 0.25% of the mass of the Earth. Charon has a diameter of about 1172 kilometers (728 miles) and a mass of about 22% that of Pluto. The two worlds circle their common center of mass with a period of 6.387 days and are locked in a "super-synchronous" rotation: observers on Pluto's surface would always see Charon in the same part of the sky relative to their local horizon.
Normally Pluto is considered the most distant world in the solar system, but during the period from January 1979 until February 1999 it was actually closer to the Sun than Neptune. It has the most eccentric and inclinced orbit of any of the major planets. This orbit won't bring Pluto back to its discovery position until the year 2178!
Plasma objects[edit | edit source]
The New Horizons Particles and Plasma team has discovered a region of cold, dense ionized gas tens of thousands of miles beyond Pluto -- the planet's atmosphere being stripped away by the solar wind and lost to space.
2015 TG387[edit | edit source]
387 (nicknamed The Goblin for the letters TG and because its discovery was near Halloween), is a trans-Neptunian object (TNO) and sednoid in the outermost part of the Solar System. It was first observed on October 13, 2015, with the Subaru Telescope at Mauna Kea Observatories, and publicly announced on October 1, 2018.
As of 2018, the object is 80 AU from the Sun; about two-and-a-half times farther out than Pluto’s orbit. As with Sedna, it would not have been found had it not been on the inner leg of its long orbit, which suggests that there may be many similar objects, most too distant to be detected by contemporary technological methods, and implies a population of about 2 million Hills cloud, or inner Oort cloud, objects larger than 40 km (25 mi), with a combined total mass of 1022 kg, which is several times the mass of the asteroid belt.
Cubewanos[edit | edit source]
The classical objects (cubewanos) are very different from the scattered objects: more than 30% of all cubewanos are on low-inclination, near-circular orbits whose eccentricities peak at 0.25. Classical objects possess eccentricities ranging from 0.2 to 0.8. Though the inclinations of scattered objects are similar to the more extreme KBOs, very few scattered objects have orbits as close to the ecliptic as much of the KBO population.
Although motions in the scattered disc are random, they do tend to follow similar directions, which means that SDOs can become trapped in temporary resonances with Neptune. Examples of possible resonant orbits within the scattered disc include 1:3, 2:7, 3:11, 5:22 and 4:79.
Plutinos[edit | edit source]
The Kuiper belt is a relatively thick torus (or "doughnut") of space, extending from about 30 to 50 AU comprising two main populations of Kuiper belt objects (KBOs): the classical Kuiper-belt objects (or "cubewanos"), which lie in orbits untouched by Neptune, and the resonant Kuiper-belt objects; those which Neptune has locked into a precise orbital ratio such as 2:3 (the object goes around twice for every three Neptune orbits) and 1:2 (the object goes around once for every two Neptune orbits). These ratios, called orbital resonances, allow KBOs to persist in regions which Neptune's gravitational influence would otherwise have cleared out over the age of the Solar System, since the objects are never close enough to Neptune to be scattered by its gravity. Those in 2:3 resonances are known as "plutinos", because Pluto is the largest member of their group, whereas those in 1:2 resonances are known as "resonant trans-Neptunian object#1:2 resonance ("twotinos", period ~330 years) twotinos".
Kuiper belts[edit | edit source]
"[B]roadband optical photometry of Centaurs and Kuiper Belt objects from the Keck 10 m, the University of Hawaii 2.2 m, and the Cerro Tololo InterAmerican (CTIO) 1.5 m telescopes [shows] a wide dispersion in the optical colors of the objects, indicating nonuniform surface properties. The color dispersion [may] be understood in the context of the expected steady reddening due to bombardment by the ubiquitous flux of cosmic rays."
In the image at right, objects in the main part of the Kuiper belt are coloured green, while scattered objects are coloured orange. The four outer planets are blue. Neptune's few known trojans are yellow, while Jupiter's are pink. The scattered objects between Jupiter's orbit and the Kuiper belt are known as centaurs. The scale is in astronomical units. The pronounced gap at the bottom is due to difficulties in detection against the background of the plane of the Milky Way.
- Red = The Sun
- Aquamarine = Giant Planet
- Lime Green = Kuiper belt object
- Magenta = Trojan of Jupiter
- Yellow = Trojan of Neptune
Positions are accurate for January 1st, 2000 (J2000 epoch) with some caveats:
For planets, positions should be exact.
For minor bodies, positions are extrapolated from other epochs assuming purely Keplerian motion. As all data is from an epoch between 1993 and 2007, this should be a reasonable approximation.
Radial "spokes" of higher density in this image, or gaps in particular directions are due to observational bias (i.e. where objects were searched for), rather than any real physical structure. The pronounced gap at the bottom is due to obscuration by the band of the Milky Way.
1995 TL 95[edit | edit source]
The first object presently classified as an SDO to be discovered was 1995 TL8, found in 1995 by Spacewatch.
1996 TL 96[edit | edit source]
1999 CV 118[edit | edit source]
Three more were identified by the same survey in 1999: 1999 CV118, 1999 CY118, and 1999 CF119.
2011 SDOs[edit | edit source]
As of 2011, over 200 SDOs have been identified, including 229762 Gǃkúnǁʼhòmdímà|Gǃkúnǁʼhòmdímà (discovered by Schwamb, Brown, and Rabinowitz), 2002 TC302 (Near Earth Asteroid Tracking NEAT), Eris (Brown, Trujillo, and Rabinowitz), 90377 Sedna Sedna (Brown, Trujillo, and Rabinowitz) and 2004 VN112 (Deep Ecliptic Survey). Although the numbers of objects in the Kuiper belt and the scattered disc are hypothesized to be roughly equal, observational bias due to their greater distance means that far fewer SDOs have been observed to date.
Oort clouds[edit | edit source]
The Oort cloud or the Öpik–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 outer limit of the Oort cloud defines the cosmographical boundary of the Solar System and the region of the Sun's gravitational dominance.
Known trans-Neptunian objects are often divided into two subpopulations: the Kuiper belt and the scattered disc. A third reservoir of trans-Neptunian objects, the Oort cloud, has been hypothesized, although no confirmed direct observations of the Oort cloud have been made. Some researchers further suggest a transitional space between the scattered disc and the inner Oort cloud, populated with "detached objects".
Neptune objects[edit | edit source]
In contrast to the Kuiper belt, the scattered-disc population can be disturbed by Neptune. Scattered-disc objects come within gravitational range of Neptune at their closest approaches (~30 AU) but their farthest distances reach many times that. Ongoing research suggests that the centaurs, a class of icy planetoids that orbit between Jupiter and Neptune, may simply be SDOs thrown into the inner reaches of the Solar System by Neptune, making them "cis-Neptunian" rather than trans-Neptunian scattered objects. Some objects, like (29981) 1999 TD10, blur the distinction and the Minor Planet Center (MPC), which officially catalogues all trans-Neptunian objects, now lists centaurs and SDOs together.
The MPC, however, makes a clear distinction between the Kuiper belt and the scattered disc, separating those objects in stable orbits (the Kuiper belt) from those in scattered orbits (the scattered disc and the centaurs). However, the difference between the Kuiper belt and the scattered disc is not clear-cut, and many astronomers see the scattered disc not as a separate population but as an outward region of the Kuiper belt. Another term used is "scattered Kuiper-belt object" (or SKBO) for bodies of the scattered disc.
The difference between objects in the Kuiper belt and scattered-disc objects is that the latter bodies "are transported in semi-major axis by close and distant encounters with Neptune," but the former experienced no such close encounters. This delineation is inadequate (as they note) over the age of the Solar System, since bodies "trapped in resonances" could "pass from a scattering phase to a non-scattering phase (and vice versa) numerous times." That is, trans-Neptunian objects could travel back and forth between the Kuiper belt and the scattered disc over time. Therefore, they chose instead to define the regions, rather than the objects, defining the scattered disc as "the region of orbital space that can be visited by bodies that have encountered Neptune" within the radius of a Hill sphere, and the Kuiper belt as its "complement ... in the a > 30 AU region"; the region of the Solar System populated by objects with semi-major axes greater than 30 AU.
The scattered disc is a very dynamic environment. Because they are still capable of being perturbed by Neptune, SDOs' orbits are always in danger of disruption; either of being sent outward to the Oort cloud or inward into the centaur population and ultimately the Jupiter family of comets. For this reason Gladman et al. prefer to refer to the region as the scattering disc, rather than scattered. Unlike Kuiper-belt objects (KBOs), the orbits of scattered-disc objects can be inclined as much as 40° from the ecliptic.
Sedna[edit | edit source]
Sedna was discovered from an image dated 2003-11-14 at coordinates 03 15 10.09 +05 38 16.5. The 3 overexposed stars are apparent magnitude 13. The "bright star" near Sedna is apmag 14.9 and about the same magnitude as Pluto. (Wikisky image of this region) The picture shows an area of the sky equal to the area covered by a pinhead held at arm's length. Sedna is too faint to be seen by all but the most powerful amateur telescopes.
The Minor Planet Center classifies the trans-Neptunian object 90377 Sedna as a scattered-disc object. Sedna should be considered an inner Oort-cloud object rather than a member of the scattered disc, because, with a perihelion distance of 76 AU, it is too remote to be affected by the gravitational attraction of the outer planets.  Under this definition, an object with a perihelion greater than 40 AU could be classified as outside the scattered disc. 
2000 CR 105[edit | edit source]
(148209) 2000 CR105 (discovered before Sedna) and 2004 VN112 have a perihelion too far away from Neptune to be influenced by it. This led to a discussion among astronomers about a new minor planet set, called the extended scattered disc (E-SDO). 2000 CR105 may also be an inner Oort-cloud object or (more likely) a transitional object between the scattered disc and the inner Oort cloud. More recently, these objects have been referred to as "detached", or distant detached objects (DDO).
There are no clear boundaries between the scattered and detached regions. Gomes et al. define SDOs as having "highly eccentric orbits, perihelia beyond Neptune, and semi-major axes beyond the 1:2 resonance." By this definition, all distant detached objects are SDOs. Since detached objects' orbits cannot be produced by Neptune scattering, alternative scattering mechanisms have been put forward, including a passing star or a distant, planet-sized object.
Scattered near objects[edit | edit source]
Scattered-near (i.e. typical SDOs) and scattered-extended (i.e. detached objects), where scattered-near objects are those whose orbits are non-resonant, non-planetary-orbit-crossing and have a Tisserand parameter (relative to Neptune) less than 3, and scattered-extended objects have a Tisserand parameter (relative to Neptune) greater than 3 and have a time-averaged eccentricity greater than 0.2.
10-million-year orbits[edit | edit source]
A 10-million-year orbit integration is used instead of the Tisserand parameter. An object qualifies as an SDO if its orbit is not resonant, has a semi-major axis no greater than 2000 AU, and, during the integration, its semi-major axis shows an excursion of 1.5 AU or more. Gladman et al. suggest the term scattering disk object to emphasize this present mobility. If the object is not an SDO as per the above definition, but the eccentricity of its orbit is greater than 0.240, it is classified as a detached TNO. (Objects with smaller eccentricity are considered classical.) In this scheme, the disc extends from the orbit of Neptune to 2000 AU, the region referred to as the inner Oort cloud.
Medium and high eccentricities[edit | edit source]
SDOs are typically characterized by orbits with medium and high eccentricities with a semi-major axis greater than 50 AU, but their perihelia bring them within influence of Neptune. Having a perihelion of roughly 30 AU is one of the defining characteristics of scattered objects, as it allows Neptune to exert its gravitational influence.
Eris[edit | edit source]
136199 Eris was measured to be 2,326 ± 12 kilometers (1,445.3 ± 7.5 mi) in diameter. Eris's mass is about 0.27% of the Earth mass, about 27% more than dwarf planet Pluto, although Pluto is slightly larger by volume.
Eris is a trans-Neptunian object (TNO), a member of a high-orbital eccentricity population known as the scattered disk, with one known natural satellite, Dysnomia, at a distance from the Sun of 96.3 astronomical units (1.441×1010 km; 8.95×109 mi), roughly three times that of Pluto. With the exception of some long-period comets, until 2018 VG18 was discovered on December 17, 2018, Eris and Dysnomia were the most distant known natural objects in the Solar System.
Observations of a stellar occultation by Eris in 2010 showed that its diameter was 2,326 ± 12 kilometers (1,445.3 ± 7.5 mi), very slightly less than Pluto, which was measured by New Horizons as 2,376.6 ± 3.6 kilometers (1,476.8 ± 2.2 mi) in July 2015.
Eris is a trans-Neptunian dwarf planet (plutoid). Its orbital characteristics more specifically categorize it as a scattered-disk object (SDO), or a TNO that has been "scattered" from the Kuiper belt into more-distant and unusual orbits following gravitational interactions with Neptune as the Solar System was forming. Although its high orbital inclination is unusual among the known SDOs, theoretical models suggest that objects that were originally near the inner edge of the Kuiper belt were scattered into orbits with higher inclinations than objects from the outer belt.
Haumea[edit | edit source]
Haumea (minor-planet designation 136108 Haumea, initially, (136108) 2003 EL61) is a dwarf planet located beyond Neptune's orbit. It was discovered on December 28, 2004, just after Christmas, at the Palomar Observatory. Precovery images of Haumea have been identified back to March 22, 1955.
Haumea is a plutoid, a dwarf planet located beyond Neptune's orbit. The nominal trajectory suggests that Haumea is in a weak 7:12 orbital resonance with Neptune, which would make it a resonant trans-Neptunian object instead. There are precovery images of Haumea dating back to March 22, 1955 from the Palomar Mountain Digitized Sky Survey.
Haumea's orbit has a slightly greater orbital eccentricity than that of the other members of the Haumea family, 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 mechanism, or Kozai effect, which allows the exchange of an orbit's inclination for increased eccentricity.
With a visual magnitude of 17.3, Haumea is the third-brightest object in the Kuiper belt after Pluto and Makemake, and easily observable with a large amateur telescope. However, because the planets and most small Solar System bodies share a invariable plane, or common orbital alignment, from their formation in the protoplanetary, primordial disk, of the Solar System, most early surveys for distant objects focused on the projection on the sky of this common plane, called the ecliptic. As the region of sky close to the ecliptic became well explored, later sky surveys began looking for objects that had been dynamically excited into orbits with higher inclinations, as well as more distant objects, with slower mean motions across the sky.
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. While most rotating bodies in equilibrium are flattened into oblate spheroids, Haumea rotates so quickly that it is distorted into a triaxial ellipsoid. If Haumea were to rotate much more rapidly, it would distort itself into a dumbbell shape and split in two. This rapid rotation is thought to have been caused by the impact that created its satellites and collisional family. Because Haumea has moons, the mass of the system can be calculated from their orbits using Kepler's third law. The result is 4.2×1021 kg, 28% the mass of the Plutonian system and 6% that of the Moon. Nearly all of this mass is in Haumea.
For most distant objects, the albedo is unknown, but Haumea is large and bright enough for its infrared, thermal emission to be measured, which has given an approximate value for its albedo and thus its size.
The rigid body dynamics, specifically, rotational physics of deformable bodies predicts that over as little as a hundred days, a body rotating as rapidly as Haumea will have been distorted into the hydrostatic equilibrium form of a triaxial ellipsoid. It is thought that most of the fluctuation in Haumea's brightness is caused not by local differences in albedo but by the alternation of the side view and end view as seen from Earth.
If Haumea were in hydrostatic equilibrium and had a low density like Pluto, with a thick mantle of volatiles, such as ice, over a small silicate, rocky core, its rapid rotation would have elongated it to a greater extent than the fluctuations in its brightness allow. Such considerations constrained its density to a range of 2.6–3.3 g/cm3.
In 2005, the Gemini Observatory and Keck Observatory telescopes obtained spectra of Haumea which showed strong crystalline water ice features similar to the surface of Pluto's moon Charon. This is peculiar, because crystalline ice forms at temperatures above 110 K, whereas Haumea's surface temperature is below 50 K, a temperature at which amorphous ice is formed. In addition, the structure of crystalline ice is unstable under the constant rain of cosmic rays and energetic particles from the Sun that strike trans-Neptunian objects. The timescale for the crystalline ice to revert to amorphous ice under this bombardment is on the order of ten million years, yet trans-Neptunian objects have been in their present cold-temperature locations for timescales of billions of years. Radiation damage should also redden and darken the surface of trans-Neptunian objects where the common surface materials of organic molecular ices and tholin-like compounds are present, as is the case with Pluto. Therefore, the spectra and colour suggest Haumea and its family members have undergone recent resurfacing that produced fresh ice. However, no plausible resurfacing mechanism has been suggested.
Haumea is as bright as snow, with an albedo in the range of 0.6–0.8, consistent with crystalline ice. Other large TNOs such as Eris appear to have albedos as high or higher. Best-fit modeling of the surface spectra suggested that 66% to 80% of the Haumean surface appears to be pure crystalline water ice, with one contributor to the high albedo possibly hydrogen cyanide or phyllosilicate clays. Inorganic cyanide salts such as copper potassium cyanide may also be present.
Visible and near infrared spectra suggest a homogeneous surface covered by an intimate 1:1 mixture of amorphous and crystalline ice, together with no more than 8% organics. The absence of ammonia hydrate excludes cryovolcanism and the observations confirm that the collisional event must have happened more than 100 million years ago, in agreement with the dynamic studies. The absence of measurable methane in the spectra of Haumea is consistent with a warm collisional history that would have removed such volatiles, in contrast to Makemake.
Interstellar comets[edit | edit source]
An interstellar object is an astronomical object that is located in interstellar space including objects that are on an interstellar trajectory but are temporarily passing close to a star, such as certain asteroids and comets (including exocomets)
The image on the right shows `Oumuamua's hyperbolic trajectory across the full solar system, with annual markers, and planet positions on 1/1/2018.
"A newly discovered comet is screaming away from Earth, and based on its weird orbital trajectory might be the first comet ever observed to come from interstellar space. A sky-surveying telescope in Hawaii spotted the fast-moving object, now called C/2017 U1, on 18 October, after its closest approach to the sun. The following week, astronomers made 34 separate observations of the object and found it has a strange trajectory that doesn't appear to circle the sun."
ʻOumuamua showed no signs of a cometary coma despite its close approach to the Sun, but underwent non-gravitational acceleration which is seen in many icy comets, although other reasons have been suggested.
It is possible for objects orbiting a star to be ejected due to interaction with a third massive body, such a process was initiated in early 1980s when C/1980 E1, initially gravitationally bound to the Sun, passed near Jupiter and was accelerated sufficiently to reach escape velocity from the Solar System, changing its orbit from elliptical to hyperbolic and making it the most eccentric known object at the time, with an eccentricity of 1.057. It is headed for interstellar space.
Asteroid (514107) 2015 BZ509 may be a former interstellar object, captured some 4.5 billion years ago, as evidenced by its co-orbital motion with Jupiter and its retrograde orbit around the Sun.
An interstellar comet can probably, on rare occasions, be captured into a heliocentric orbit while passing through the Solar System. Computer simulations show that Jupiter is the only planet massive enough to capture one, and that this can be expected to occur once every sixty million years. Comets Machholz 1 and Comet Hyakutake C/1996 B2 are possible examples of such comets, as they have atypical chemical makeups for comets in the Solar System.
Current models of Oort cloud formation predict that more comets are ejected into interstellar space than are retained in the Oort cloud, with estimates varying from 3 to 100 times as many. Other simulations suggest that 90–99% of comets are ejected. There is no reason to believe comets formed in other star systems would not be similarly scattered.
A more recent estimate, following the detection of 'Oumuamua, predicts that "The steady-state population of similar, ~100 m scale interstellar objects inside the orbit of Neptune is ~1×104, each with a residence time of ~10 years."
There should be hundreds of 'Oumuamua-size interstellar objects in the Solar System, based on calculated orbital characteristics, with known examples: 2011 SP25, 2017 RR2, 2017 SV13, and 2018 TL6. These are all orbiting the sun, but with unusual orbits, and are assumed to have been trapped at some occasion.
See also[edit | edit source]
References[edit | edit source]
- Maggie Masetti. (2007). Cosmic Distance Scales – The Solar System. Website of NASA's High Energy Astrophysics Science Archive Research Center. Retrieved 2008 07-12.
- Morbidelli, Alessandro (2005). "Origin and dynamical evolution of comets and their reservoirs". arXiv:astro-ph/0512256.
- McFadden, Weissman, & Johnson (2007). Encyclopedia of the Solar System, footnote p. 584
- WikiPedant (4 November 2007). "periodic comet". San Francisco, California: Wikimedia Foundation, Inc. Retrieved 14 June 2019.
- jf. The Jupiter Family Comets. Washington, DC: Carnegie Institution of Washington. p. 1. Retrieved 5 February 2018.
- yfernandez (28 July 2015). List of Jupiter-Family and Halley-Family Comets. Orlando, FL: University of Central Florida. p. 1. Retrieved 5 February 2018.
- Horner, J.; Evans, N. W.; Bailey, Mark E. (2004). "Simulations of the Population of Centaurs I: The Bulk Statistics". Monthly Notices of the Royal Astronomical Society 354 (3): 798. doi:10.1111/j.1365-2966.2004.08240.x.
- SnoopY (21 December 2005). "Centaur". San Francisco, California: Wikimedia Foundation, Inc. Retrieved 31 August 2015.
- V. V. Emel’yanenko (December 2005). "Structure and dynamics of the Centaur population: constraints on the origin of short-period comets". Earth, Moon, and Planets 97 (3-4): 341-51. doi:10.1007/s11038-006-9095-5. http://dccm.susu.ac.ru/acm2005.pdf. Retrieved 2011-10-06.
- Fathi Namouni and Maria Helena Moreira Morais (May 2, 2018). "An interstellar origin for Jupiter's retrograde co-orbital asteroid". Monthly Notices of the Royal Astronomical Society 477 (1): L117–L121. doi:10.1093/mnrasl/sly057. https://academic.oup.com/mnrasl/article/477/1/L117/4996014. For criticism of this idea see Billings, Lee (21 May 2018). "Astronomers Spot Potential "Interstellar" Asteroid Orbiting Backward around the Sun". Scientific American. Retrieved 1 June 2018.
- Jewitt, David; Haghighipour, Nader (2007). "Irregular Satellites of the Planets: Products of Capture in the Early Solar System". Annual Review of Astronomy and Astrophysics 45 (1): 261–95. doi:10.1146/annurev.astro.44.051905.092459. Archived from the original on 2010-02-07. https://www.webcitation.org/5nMMZRRKe?url=http://www.ifa.hawaii.edu/~jewitt/papers/2007/JH07.pdf.
- "Unusual Minor Planets". Minor Planet Center. Retrieved 2010-10-25.
- "Orbit Classification (Centaur)". JPL Solar System Dynamics. Retrieved 2008-10-13.
- Elliot, J.L.; Kern, S. D.; Clancy, K. B.; Gulbis, A. A. S.; Millis, R. L.; Buie, M. W.; Wasserman, L. H.; Chiang, E. I. et al. (2005). "The Deep Ecliptic Survey: A Search for Kuiper Belt Objects and Centaurs. II. Dynamical Classification, the Kuiper Belt Plane, and the Core Population". The Astronomical Journal 129 (2): 1117–1162. doi:10.1086/427395. http://www.iop.org/EJ/abstract/1538-3881/129/2/1117. Retrieved 2008-09-22.
- Gladman, B.; Marsden, B.; Van Laerhoven, C. (2008). "Nomenclature in the Outer Solar System". The Solar System Beyond Neptune. ISBN 978-0-8165-2755-7. http://www.lpi.usra.edu/books/ssbn2008/7002.pdf.
- Chaing, Eugene; Lithwick, Y.; Murray-Clay, R.; Buie, M.; Grundy, W.; Holman, M. (2007). "A Brief History of Transneptunian Space". Protostars and Planets V (University of Arizona Press, Tucson): 895–911.
- "JPL Small-Body Database Search Engine: List of centaurs". JPL Solar System Dynamics. Retrieved 2018-10-11.
- "JPL Small-Body Database Search Engine: List of TNOs with perihelia closer than Uranus's orbit". JPL Solar System Dynamics. Retrieved 2018-10-11.
- Grundy, Will; Stansberry, J.A.; Noll, K; Stephens, D.C.; Trilling, D.E.; Kern, S.D.; Spencer, J.R.; Cruikshank, D.P. et al. (2007). "The orbit, mass, size, albedo, and density of (65489) Ceto/Phorcys: A tidally-evolved binary Centaur". Icarus 191 (1): 286–297. doi:10.1016/j.icarus.2007.04.004.
- Brown, Michael E. "How many dwarf planets are there in the outer solar system? (updates daily)". California Institute of Technology. Retrieved 18 November 2016.
- Barucci, M. A.; Doressoundiram, A.; Cruikshank, D. P. (2003). "Physical Characteristics of TNOs and Centaurs" (PDF). Laboratory for Space Studies and Astrophysics Instrumentation, Paris Observatory. Archived from the original (PDF) on 29 May 2008. Retrieved 20 March 2008.
- Sheppard, Scott S. (October 16–18, 2005). "Small Bodies in the Outer Solar System" (PDF). New Horizons in Astronomy: Frank N. Bash Symposium 2005. Austin, Texas: Astronomical Society of the Pacific. pp. 3–14. ISBN 1-58381-220-2. Archived from the original (PDF) on 2006-10-12. Retrieved 2008-08-14.
- "List Of Transneptunian Objects". Minor Planet Center. Retrieved 23 October 2018.
- "List Of Centaurs and Scattered-Disk Objects". Minor Planet Center. 8 October 2018. Retrieved 23 October 2018.
- "List of Known Trans-Neptunian Objects". Johnston's Archive. 7 October 2018. Retrieved 23 October 2018.
- "JPL Small-Body Database Search Engine: orbital class (TNO)". JPL Solar System Dynamics. Retrieved 2014-07-10.
- "JPL Small-Body Database Search Engine: orbital class (TNO) and q > 30.1 (AU)". Retrieved 2014-07-11.
- C. de la Fuente Marcos; R. de la Fuente Marcos (September 1, 2014). "Extreme trans-Neptunian objects and the Kozai mechanism: signalling the presence of trans-Plutonian planets". Monthly Notices of the Royal Astronomical Society 443 (1): L59–L63. doi:10.1093/mnrasl/slu084.
- Chris Gebhardt; Jeff Goldader (August 20, 2011). "Thirty-four years after launch, Voyager 2 continues to explore". NASASpaceflight.
- Rabinowitz, David L.; Barkume, K. M.; Brown, Michael E.; Roe, H. G.; Schwartz, M.; Tourtellotte, S. W.; Trujillo, C. A. (2006). "Photometric Observations Constraining the Size, Shape, and Albedo of 2003 El61, a Rapidly Rotating, Pluto-Sized Object in the Kuiper Belt". Astrophysical Journal 639 (2): 1238–1251. doi:10.1086/499575.
- Fornasier, S.; Dotto, E.; Hainaut, O.; Marzari, F.; Boehnhardt, H.; De Luise, F. et al. (October 2007). "Visible spectroscopic and photometric survey of Jupiter Trojans: Final results on dynamical families". Icarus 190 (2): 622–642. doi:10.1016/j.icarus.2007.03.033.
- Deborah Netburn (14 July 2015). Pluto is now the most distant object ever visited by humanity. Los Angeles, California USA: Los Angeles Times. Retrieved 2015-07-14.
- Jeff Moore (21 July 2015). High resolution photo shows another set of ice mountains on Pluto. Mashable.com. Retrieved 2015-07-23.
- Miriam Kramer (21 July 2015). High resolution photo shows another set of ice mountains on Pluto. Mashable.com. Retrieved 2015-07-23.
- Guarino, Ben (October 2, 2018). New dwarf planet spotted at the very fringe of our solar system, In: The Washington Post. Retrieved October 3, 2018.
- Chang, Kenneth (October 2, 2018). A Goblin World That Points Toward Hidden Planet Nine in the Solar System, In: The New York Times. Retrieved October 2, 2018.
- Mortillaro, Nicole (October 2, 2018). Discovery of new object supports theory of 'super-Earth' at edge of solar system, In: CBC News. Retrieved October 2, 2018.
- MPEC 2018-T05 : 2015 TG387. IAU Minor Planet Center. October 1, 2018. Retrieved October 2, 2018.
- Witze, Alexandra (October 1, 2018). ‘Goblin’ world found orbiting at the edges of the Solar System. Nature. doi:10.1038/d41586-018-06885-1. Retrieved October 2, 2018.
- Sheppard, Scott; Trujillo, Chadwick; Tholen, David; Kaib, Nathan (September 28, 2018). A New High Perihelion Inner Oort Cloud Object (PDF). arXiv:1810.00013. Retrieved October 2, 2018.
- JPL Small-Body Database Search Engine: a > 150 (AU) and q > 50 (AU) and data-arc span > 365 (d). JPL Solar System Dynamics. Retrieved October 2, 2018.
- Levison, Harold F.; Morbidelli, Alessandro (2003-11-27). "The formation of the Kuiper belt by the outward transport of bodies during Neptune's migration". Nature 426 (6965): 419–421. doi:10.1038/nature02120. PMID 14647375. http://www.nature.com/nature/journal/v426/n6965/abs/nature02120.html. Retrieved 2012-05-26.
- Levison, Harold F.; Donnes, Luke (2007). "Comet Populations and Cometary Dynamics". In Adams McFadden, Lucy Ann; Weissman, Paul Robert; Johnson, Torrence V. (eds.). Encyclopedia of the Solar System (2nd ed.). Amsterdam; Boston: Academic Press. pp. 575–588. ISBN 978-0-12-088589-3. Archived from the original on 2015-09-06.
- Gomes, Rodney S.; Fernandez, Julio A.; Gallardo, Tabare; Brunini, Adrian (2008). "The Scattered Disk: Origins, Dynamics and End States" (PDF). Universidad de la Republica, Uruguay. Retrieved 2008-08-10.
- De Sanctis, M. C.; Capria, M. T.; Coradini, A. (2001). "Thermal Evolution and Differentiation of Edgeworth-Kuiper Belt Objects". The Astronomical Journal 121 (5): 2792–2799. doi:10.1086/320385.
- Alan Stern; Colwell, Joshua E. (1997). "Collisional Erosion in the Primordial Edgeworth-Kuiper Belt and the Generation of the 30–50 AU Kuiper Gap". The Astrophysical Journal 490 (2): 879–882. doi:10.1086/304912.
- Jane Luu and David Jewitt (November 1996). "Color Diversity among the Centaurs and Kuiper Belt Objects". The Astronomical Journal 112 (5): 2310-8. http://adsabs.harvard.edu/full/1996AJ....112.2310L. Retrieved 2013-11-05.
- The MPC Orbit (MPCORB) Database.
- Carl D. Murray and Stanley F. Dermott (1999). Solar System Dynamics. Cambridge University Press. ISBN 0 521 57295 9.
- Schmadel, Lutz D. (2003); Dictionary of Minor Planet Names (5th rev. and enlarged ed. edition). Berlin: Springer. Page 925 (Appendix 10). Also see McFadden, Lucy-Ann; Weissman, Paul & Johnson, Torrence (1999). Encyclopedia of the Solar System. San Diego: Academic Press. Page 218.
- Luu, Jane X.; Marsden, Brian G.; Jewitt, David C. (5 June 1997). "A new dynamical class of object in the outer Solar System". Nature 387 (6633): 573–575. doi:10.1038/42413. Archived from the original on August 12, 2007. https://web.archive.org/web/20070812095854/http://www.ifa.hawaii.edu/faculty/jewitt/papers/TL66_1996/TL66.pdf. Retrieved 2008-08-02.
- Davies, John Keith (2001). Beyond Pluto: Exploring the Outer Limits of the Solar System (PDF). Cambridge University Press. p. 111. ISBN 978-0-521-80019-8. Retrieved 2008-07-02.
- Jewitt, David C. (August 2009). "Scattered Kuiper Belt Objects (SKBOs)". Institute for Astronomy. Retrieved 2010-01-23.
- IAU: Minor Planet Center (2011-01-03). "List Of Centaurs and Scattered-Disk Objects". Central Bureau for Astronomical Telegrams, Harvard-Smithsonian Center for Astrophysics. Retrieved 2011-01-03.
- Schwamb, M. E.; Brown, Michael E.; Rabinowitz, Davdi; Marsden, Brian G. (2008). "2007 UK126". Minor Planet Electronic Circ. 2008-D38: 38.
- Staff (2007-05-01). "Discovery Circumstances: Numbered Minor Planets". Minor Planet Center. Retrieved 2010-10-25.
- "Discovery Circumstances: Numbered Minor Planets (90001)-(95000)". Minor Planet Center. Retrieved 2010-10-25.
- Marc W. Buie (2007-11-08). "Orbit Fit and Astrometric record for 04VN112". SwRI (Space Science Department). Archived from the original on 2010-08-18. Retrieved 2008-07-17.
- Fred Lawrence Whipple, G. Turner, J. A. M. McDonnell, M. K. Wallis (1987-09-30). "A Review of Cometary Sciences". Philosophical Transactions of the Royal Society A (Royal Society Publishing) 323 (1572): 339–347 . doi:10.1098/rsta.1987.0090. http://rsta.royalsocietypublishing.org/content/323/1572/339.short.
- Alessandro Morbidelli (2006). Origin and dynamical evolution of comets and their reservoirs of water ammonia and methane. arXiv:astro-ph/0512256.
- Kuiper Belt & Oort Cloud. NASA. Retrieved 2011-08-08.
- Morbidelli, Alessandro; Brown, Michael E. (2004-11-01). "The Kuiper Belt and the Primordial Evolution of the Solar System" (PDF). In M. C. Festou; H. U. Keller; H. A. Weaver (eds.). Comets II. Tucson (AZ): University of Arizona Press. pp. 175–91. ISBN 978-0-8165-2450-1. OCLC 56755773. Retrieved 2008-07-27.
- Morbidelli, Alessandro; Levison, Harold F. (2007). "Kuiper Belt Dynamics". In Lucy-Ann Adams McFadden; Paul Robert Weissman; Torrence V. Johnson (eds.). Encyclopedia of the Solar System (2nd ed.). Amsterdam; Boston: Academic Press. pp. 589–604. ISBN 978-0-12-088589-3.
- Horner, J.; Evans, N. W.; Bailey, Mark E.; Asher, D. J. (2003). "The Populations of Comet-like Bodies in the Solar System". Monthly Notices of the Royal Astronomical Society 343 (4): 1057–1066. doi:10.1046/j.1365-8711.2003.06714.x.
- Remo notes that Cis-Neptunian bodies "include terrestrial and large gaseous planets, planetary moons, asteroids, and main-belt comets within Neptune's orbit." (Remo 2007)
- Silber, Kenneth (1999). "New Object in Solar System Defies Categories". space.com. Archived from the original on September 21, 2005. Retrieved 2008-08-12.
- Jewitt, David C. (2008). "The 1000 km Scale KBOs". Retrieved 2010-01-23.
- Bertoldi, F.; Altenhoff, W.; Weiss, A.; Menten, K. M.; Thum, C. (2 February 2006). "The trans-Neptunian object UB313 is larger than Pluto". Nature 439 (7076): 563–564. doi:10.1038/nature04494. PMID 16452973.
- Brown, Michael E. "Sedna (The coldest most distant place known in the solar system; possibly the first object in the long-hypothesized Oort cloud)". California Institute of Technology, Department of Geological Sciences. Retrieved 2008-07-02.
- Lykawka, Patryk Sofia; Mukai, Tadashi (2007). "Dynamical classification of trans-Neptunian objects: Probing their origin, evolution, and interrelation". Icarus (Kobe) 189 (1): 213–232. doi:10.1016/j.icarus.2007.01.001. http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6WGF-4MY0MMW-3&_user=10&_rdoc=1&_fmt=&_orig=search&_sort=d&view=c&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=263a1288080d4fc7cd1d53d76f7dc580. Retrieved 2008-07-24.
- Gladman, Brett J. "Evidence for an Extended Scattered Disk?". Observatoire de la Cote d'Azur. Retrieved 2008-08-02.
- Jewitt, David C.; Delsanti, A. (2006). "The Solar System Beyond The Planets". Solar System Update : Topical and Timely Reviews in Solar System Sciences. Springer-Praxis Ed. ISBN 978-3-540-26056-1. (Preprint version (pdf))
- Gomes, Rodney S.; Matese, John J.; Lissauer, Jack J. (October 2006). "A distant planetary-mass solar companion may have produced distant detached objects". Icarus 184 (2): 589–601. doi:10.1016/j.icarus.2006.05.026.
- Morbidelli, Alessandro; Levison, Harold F. (November 2004). "Scenarios for the Origin of the Orbits of the Trans-Neptunian Objects 2000 CR105 and 2003 VB12". The Astronomical Journal 128 (5): 2564–2576. doi:10.1086/424617. http://www.iop.org/EJ/abstract/1538-3881/128/5/2564/. Retrieved 2008-07-02.
- Elliot, J. L.; Kern, S. D.; Clancy et al., K. B. (2005). "The Deep Ecliptic Survey: A Search for Kuiper Belt Objects and Centaurs. II. Dynamical Classification, the Kuiper Belt Plane, and the Core Population". The Astronomical Journal 129 (2): 1117–1162. doi:10.1086/427395. Archived from the original on June 25, 2008. https://web.archive.org/web/20080625140652/http://alpaca.as.arizona.edu/~trilling/des2.pdf.
- Trujillo, Chadwick A.; Jewitt, David C.; Luu, Jane X. (2000-02-01). "Population of the Scattered Kuiper Belt". The Astrophysical Journal 529 (2): L103–L106. doi:10.1086/312467. PMID 10622765. Archived from the original on August 12, 2007. https://web.archive.org/web/20070812095910/http://www.ifa.hawaii.edu/faculty/jewitt/papers/SKBO/tjl2000.pdf. Retrieved 2008-07-02.
- Sicardy, B.; Ortiz, J. L.; Assafin, M.; Jehin, E.; Maury, A.; Lellouch, E.; Gil-Hutton, R.; Braga-Ribas, F. et al. (2011). "Size, density, albedo and atmosphere limit of dwarf planet Eris from a stellar occultation". European Planetary Science Congress Abstracts 6: 137. http://meetingorganizer.copernicus.org/EPSC-DPS2011/EPSC-DPS2011-137-8.pdf. Retrieved September 14, 2011.
- Brown, Michael E.; Schaller, Emily L. (15 June 2007). "The Mass of Dwarf Planet Eris". Science 316 (5831): 1585. doi:10.1126/science.1139415. PMID 17569855. http://hubblesite.org/pubinfo/pdf/2007/24/pdf.pdf.
- "Dwarf Planet Outweighs Pluto". space.com. 2007. Retrieved June 14, 2007.
- "How Big Is Pluto? New Horizons Settles Decades-Long Debate". www.nasa.gov. 2015. Retrieved July 14, 2015.
- "AstDys (136199) Eris Ephemerides". Department of Mathematics, University of Pisa, Italy. Retrieved February 28, 2016.
- Brown, Mike (2010). "The shadowy hand of Eris". Mike Brown's Planets. Retrieved November 7, 2010.
- Brown, Mike (November 22, 2010). "How big is Pluto, anyway?". Mike Brown's Planets. Retrieved November 23, 2010. (Franck Marchis on 2010-11-08)
- "How Big Is Pluto? New Horizons Settles Decades-Long Debate". NASA. 2015. Retrieved 2015-07-13.
- Stern, S. A.; Grundy, W.; McKinnon, W. B.; Weaver, H. A.; Young, L. A. (2017). "The Pluto System After New Horizons". Annual Review of Astronomy and Astrophysics 2018: 357–392. doi:10.1146/annurev-astro-081817-051935.
- "Pluto Now Called a Plutoid". Space.com. June 11, 2008. Retrieved June 11, 2008.
- Gomes R. S.; Gallardo T.; Fernández J. A.; Brunini A. (2005). "On the origin of the High-Perihelion Scattered Disk: the role of the Kozai mechanism and mean motion resonances". Celestial Mechanics and Dynamical Astronomy 91 (1–2): 109–129. doi:10.1007/s10569-004-4623-y.
- "IAU names fifth dwarf planet Haumea". IAU Press Release. 2008-09-17. Archived from the original on 2011-07-02. Retrieved 2008-09-17.
- "Santa et al". NASA Astrobiology Magazine. 2005-09-10. Archived from the original on 2006-04-26. Retrieved 2008-10-16.
- Michael E Brown. "The electronic trail of the discovery of 2003 EL61". CalTech. Archived from the original on 2006-09-01. Retrieved 2006-08-16.
- "Jet Propulsion Laboratory Small-Body Database Browser: 136108 Haumea (2003 EL61)" (2014-11-28 last obs). NASA's Jet Propulsion Laboratory. Archived from the original on 2015-12-27. Retrieved 2015-01-08.
- "Dwarf Planets and their Systems". US Geological Survey Gazetteer of Planetary Nomenclature. Archived from the original on 2011-06-29. Retrieved 2008-09-17.
- Ragozzine, D.; Brown, M. E. (2007). "Candidate Members and Age Estimate of the Family of Kuiper Belt Object 2003 EL61". Astronomical Journal 134 (6): 2160–2167. doi:10.1086/522334.
- Marc W. Buie (2008-06-25). "Orbit Fit and Astrometric record for 136108". Southwest Research Institute (Space Science Department). Archived from the original on 2011-05-18. Retrieved 2008-10-02.
- "HORIZONS Web-Interface". NASA Jet Propulsion Laboratory Solar System Dynamics. Archived from the original on 2008-07-18. Retrieved 2008-07-02.
- "AstDys (136108) Haumea Ephemerides". Department of Mathematics, University of Pisa, Italy. Archived from the original on 2011-06-29. Retrieved 2009-03-19.
- Brown, M. E.; Barkume, K. M.; Ragozzine, D.; Schaller, L. (2007). "A collisional family of icy objects in the Kuiper belt". Nature 446 (7133): 294–296. doi:10.1038/nature05619. PMID 17361177.
- Michael E. Brown. "The largest Kuiper belt objects" (PDF). CalTech. Archived from the original (PDF) on 2008-10-01. Retrieved 2008-09-19.
- Nesvorný, D; Roig, F. (2001). "Mean Motion Resonances in the Transneptunian Region Part II: The 1 : 2, 3 : 4, and Weaker Resonances". Icarus 150 (1): 104–123. doi:10.1006/icar.2000.6568.
- Kuchner, Marc J. (2002). "Long-Term Dynamics and the Orbital Inclinations of the Classical Kuiper Belt Objects". The Astronomical Journal 124 (2): 1221–1230. doi:10.1086/341643.
- Rabinowitz, D. L.; Barkume, Kristina; Brown, Michael E.; Roe, Henry; Schwartz, Michael; Tourtellotte, Suzanne; Trujillo, Chad (2006). "Photometric Observations Constraining the Size, Shape, and Albedo of 2003 EL61, a Rapidly Rotating, Pluto-Sized Object in the Kuiper Belt". Astrophysical Journal 639 (2): 1238–1251. doi:10.1086/499575.
- C. A. Trujillo; M. E. Brown (June 2003). "The Caltech Wide Area Sky Survey". Earth, Moon, and Planets 112 (1–4): 92–99. doi:10.1023/B:MOON.0000031929.19729.a1.
- Brown, M. E.; Trujillo, C.; Rabinowitz, D. L. (2004). "Discovery of a candidate inner Oort cloud planetoid". The Astrophysical Journal 617 (1): 645–649. doi:10.1086/422095.
- Schwamb, M. E.; Brown, M. E.; Rabinowitz, D. L. (2008). "Constraints on the distant population in the region of Sedna". American Astronomical Society, DPS Meeting #40, #38.07 40: 465.
- Agence France-Presse (2009-09-16). "Astronomers get lock on diamond-shaped Haumea". European Planetary Science Congress in Potsdam. News Limited. Archived from the original on 2009-09-23. Retrieved 2009-09-16.
- Ragozzine, D.; Brown, M. E. (2009). "Orbits and Masses of the Satellites of the Dwarf Planet Haumea = 2003 EL61". The Astronomical Journal 137 (6): 4766–4776. doi:10.1088/0004-6256/137/6/4766.
- Brown, M. E.; Bouchez, A. H.; Rabinowitz, D.; Sari, R.; Trujillo, C. A.; Van Dam, M.; Campbell, R.; Chin, J. et al. (2005). "Keck Observatory laser guide star adaptive optics discovery and characterization of a satellite to large Kuiper belt object 2003 EL61". Astrophysical Journal Letters 632 (1): L45. doi:10.1086/497641. Archived from the original on 2010-06-10. https://web.archive.org/web/20100610233232/http://www.gps.caltech.edu/%7Embrown/papers/ps/EL61.pdf.
- Stansberry, J.; Grundy, W.; Brown, M.; Cruikshank, D.; Spencer, J.; Trilling, D.; Margot, J-L. (2008). "Physical Properties of Kuiper Belt and Centaur Objects: Constraints from Spitzer Space Telescope". The Solar System Beyond Neptune (University of Arizona Press): 161.
- Alexandra C. Lockwood; Michael E. Brown; John Stansberry (2014). "The size and shape of the oblong dwarf planet Haumea". Earth, Moon, and Planets 111 (3–4): 127–137. doi:10.1007/s11038-014-9430-1.
- Chadwick A. Trujillo; Michael E. Brown; Kristina Barkume; Emily Shaller; David L. Rabinowitz (2007). "The Surface of 2003 EL61 in the Near Infrared". The Astrophysical Journal 655 (2): 1172–1178. doi:10.1086/509861.
- "Charon: An ice machine in the ultimate deep freeze". Gemini Observatory. 17 July 2007. Archived from the original on 7 June 2011. Retrieved 2007-07-18.
- Rabinowitz, D. L.; Schaefer, Bradley E.; Schaefer, Martha; Tourtellotte, Suzanne W. (2008). "The Youthful Appearance of the 2003 EL61 Collisional Family". The Astronomical Journal 136 (4): 1502–1509. doi:10.1088/0004-6256/136/4/1502.
- Brown, M. E.; Schaller, E. L.; Roe, H. G.; Rabinowitz, D. L.; Trujillo, C. A. (2006). "Direct measurement of the size of 2003 UB313 from the Hubble Space Telescope". The Astrophysical Journal Letters 643 (2): L61–L63. doi:10.1086/504843. Archived from the original on 2008-09-10. https://web.archive.org/web/20080910103928/http://www.gps.caltech.edu/~mbrown/papers/ps/xsize.pdf.
- Pinilla-Alonso, N.; Brunetto, R.; Licandro, J.; Gil-Hutton, R.; Roush, T. L.; Strazzulla, G. (2009). "Study of the Surface of 2003 EL61, the largest carbon-depleted object in the trans-neptunian belt". Astronomy and Astrophysics 496 (2): 547–556. doi:10.1051/0004-6361/200809733.
- Tegler, S. C.; Grundy, W. M.; Romanishin, W.; Consolmagno, G. J.; Mogren, K.; Vilas, F. (2007). "Optical Spectroscopy of the Large Kuiper Belt Objects 136472 (2005 FY9) and 136108 (2003 EL61)". The Astronomical Journal 133 (2): 526–530. doi:10.1086/510134.
- Valtonen, Mauri J.; Jia-Qing Zheng; Seppo Mikkola (March 1992). "Origin of oort cloud comets in the interstellar space". Celestial Mechanics and Dynamical Astronomy 54 (1–3): 37–48. doi:10.1007/BF00049542. http://www.springerlink.com/content/g43v16167077453u/. Retrieved 2008-12-30.
- Francis, Paul J. (2005-12-20). "The Demographics of Long-Period Comets". The Astrophysical Journal 635 (2): 1348–1361. doi:10.1086/497684. http://www.iop.org/EJ/article/0004-637X/635/2/1348/62880.web.pdf?request-id=035fe065-820f-4c15-b74e-1cb158b2a41d. Retrieved 2009-01-03.
- Rebecca Boyle (2017). "Glimpse of the first interstellar comet?". New scientist (3150): 15. https://dialnet.unirioja.es/servlet/articulo?codigo=6438678. Retrieved 16 February 2019.
- Micheli, M. et al. (2018). "Non-gravitational acceleration in the trajectory of 1I/2017 U1 (ʻOumuamua)". Nature 559 (7713): 223–226. doi:10.1038/s41586-018-0254-4. PMID 29950718. https://www.nature.com/articles/s41586-018-0254-4.
- Królikowska, Małgorzata; Dybczyński, Piotr A. (2013-10-01). "Near-parabolic comets observed in 2006-2010. The individualized approach to 1/a-determination and the new distribution of original and future orbits". Monthly Notices of the Royal Astronomical Society 435: 440–459. doi:10.1093/mnras/stt1313. ISSN 0035-8711. http://adsabs.harvard.edu/abs/2013MNRAS.435..440K.
- Williams, Matt (2 November 2018). "Could Oumuamua Be an Extra-Terrestrial Solar Sail?". Universe Today. Retrieved 2 November 2018.
- Bialy, Shmuel; Loeb, Abraham (26 October 2018). "Could Solar Radiation Explain ʻOumuamua's Peculiar Acceleration?". arXiv:1810.11490v4 [astro-ph.EP].
- Loeb, Abraham (26 September 2018). "How to Search for Dead Cosmic Civilizations". Scientific American. Retrieved 26 September 2018.
- Williams, Matt (1 February 2019). "Oumuamua Could be the Debris Cloud of a Disintegrated Interstellar Comet". Universe Today. Retrieved 2 February 2019.
- Sekanina, Zdenek (31 January 2019). "1I/‘Oumuamua As Debris Of Dwarf Interstellar Comet That Disintegrated Before Perihelion". arXiv. https://arxiv.org/pdf/1901.08704.pdf. Retrieved 2 February 2019.
- "JPL Small-Body Database Browser: C/1980 E1 (Bowell)" (1986-12-02 last obs). Retrieved 2010-01-08.
- "This asteroid came from another solar system—and it's here to stay". Science.
- Torbett, M. V. (July 1986). "Capture of 20 km/s approach velocity interstellar comets by three-body interactions in the planetary system". Astronomical Journal 92: 171–175. doi:10.1086/114148.
- MacRobert, Alan (2008-12-02). "A Very Oddball Comet". Sky & Telescope. Retrieved 2010-03-26.
- Mumma, M.J.; Disanti, M.A.; dello Russo, N.; Fomenkova, M.; Magee-Sauer, K.; Kaminski, C.D.; D.X. Xie (1996). "Detection of Abundant Ethane and Methane, Along with Carbon Monoxide and Water, in Comet C/1996 B2 Hyakutake: Evidence for Interstellar Origin". Science 272 (5266): 1310–1314. doi:10.1126/science.272.5266.1310. PMID 8650540.
- Choi, Charles Q. (2007-12-24). "The Enduring Mysteries of Comets". Space.com. Retrieved 2008-12-30.
- Jewitt, David; Luu, Jane; Rajagopal, Jayadev; Kotulla, Ralf; Ridgway, Susan; Liu, Wilson; Augusteijn, Thomas (2017). "Interstellar Interloper 1I/2017 U1: Observations from the NOT and WIYN Telescopes". The Astrophysical Journal 850 (2): L36. doi:10.3847/2041-8213/aa9b2f.
- Siraj, Amir; Loeb, Abraham (29 November 2018). "Identifying Interstellar Objects Trapped in the Solar System through Their Orbital Parameters". Monthly Notices of the Royal Astronomical Society 000: 1-5. https://arxiv.org/pdf/1811.09632.pdf. Retrieved 1 December 2018.