Kuiper G

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Kuiper Gürtel
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Rückblick

• 1949 K.E. Edgeworth Materiescheibe außerhalb
  Plutobahn
• 1950 J. Oort gr. sphärische Wolke von Kometen
  (1012)
• 1951 G. Kuiper Ring von Planetesimalen außerhalb
  Plutos (da kurzperiodische Kometen zeigten eine
  Konzentration zur Ekliptik)
• 1973 P.C. Joss alle kurzperiodischen Kometen
  können nicht von der Oortschen Wolke kommen

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OORTSCHE WOLKE Sie beginnt jenseits der KBOs
und ist die (noch hypothetische) Herkunftsregion
der langperiodischen Kometen. Die einige km bis
hunderte km großen Kometen bestehen fast
ausschließlich aus H2O-Schnee (schmutzige
Schneebälle).
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• 1980 Fernandez zeigte, dass eine Materiescheibe
  außerhalb der Plutobahn 300x effizienter ist für
  kurzp.Kometen
• 1983 -84 IRAS Beobachtungen Staubringe um
  Hauptreihensterne (Bsp. Beta Pictoris)
• 1988 Duncan et al. Bestätigen das Resultat von
  Fernandez
• 1992 D.C. Jewitt and J.X. Luu entdecken mit dem
  2.2 m Teleskop das erste KBO (1992 QB1)

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CLASSICAL KUIPER BELT OBJECTS (CKBOs)

• A majority of the observed Kuiper Belt Objects
  maintain large separations from Neptune even when
  at perihelion. The archetypal "Classical KBO" is
  1992 QB1. Such objects are able to survive for
  the age of the solar system without the special
  protection offered by resonances to the Plutinos,
  simply because they are already Neptune-avoiding.

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CLASSICAL KUIPER BELT OBJECTS (CKBOs)

• . The CKBOs are found mostly with semi-major axes
  between about 42 and 48 AU. The deficiency of
  more distant CKBOs is real the Classical Belt
  has an outer edge at about 50 AU (Jewitt et al.
  1998)
• The CKBOs are "classical" in the sense that
  their orbits tend to have small eccentricities as
  is expected of bodies formed by quiet
  agglomeration in a dynamically cool disk.

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CLASSICAL KUIPER BELT OBJECTS (CKBOs)

• The inclinations of the Classical KBOs range up
  to very high values (1996 RQ20 and 1997 RX9 have
  i gt 30 degrees). This suggests that the
  inclinations have been excited by some agency yet
  to be identified. Two ideas have been suggested
  for the excitation mechanism

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CLASSICAL KUIPER BELT OBJECTS (CKBOs)

• i) A few massive planetesimals might have been
  scattered into the Kuiper Belt in the early days
  by Neptune. These objects could excite the
  inclinations of the CKBOs. One problem with this
  hypothesis is that massive planetesimals (they
  would have to approach Earth mass in order to be
  effective) would also disturb and depopulate the
  resonances. That we see many Plutinos is evidence
  against the action of massive planetesimals.

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CLASSICAL KUIPER BELT OBJECTS (CKBOs)

• ii) A passing star might have stirred up the
  CKBOs. Proponents of this idea claim, based on
  numerical simulations, that the Classical objects
  can be excited while the Plutinos remain
  relatively undisturbed. One obvious problem with
  the external perturbation hypothesis is that
  passing stars rarely pass close enough to the sun
  (a miss distance of a few 100 AU is required).
  However, it is possible (likely?) that the sun
  formed with other stars in a cluster that might
  have been initially very dense. In this case, the
  early rate of close stellar passages might have
  been much higher than at present.

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CLASSICAL KUIPER BELT OBJECTS (CKBOs)

• The outer edge of the Classical Kuiper Belt, near
  50 AU, could also be a result of distrurbance by
  a close encounter with a passing star. This
  scenario has been explored by Ida et al. (2000)
• It is worth noting that stellar close approaches
  and resulting tidal truncation have been
  suggested as the cause of the sharp edged and
  small disk-like structures known as Proplyds.
  Some proplyds are only 50 AU to 100 AU across,
  similar to the diameter of the known portion of
  the Classical Kuiper Belt.

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Plutinos

• A surprising result of the new observational work
  is that many of the distant objects are in or
  near the 32 mean motion resonance with Neptune.
  This means that they complete 2 orbits around the
  sun in the time it takes Neptune to complete 3
  orbits. The same resonance is also occupied by
  Pluto. To mark the dynamical similarity with
  Pluto, we have christened these objects as
  "Plutinos" (little Plutos).

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Plutinos

• Probably, the 32 resonance acts to stabilize the
  Plutinos against gravitational perturbations by
  Neptune. Resonant objects in elliptical orbits
  can approach the orbit of Neptune without ever
  coming close to the planet itself, because their
  perihelia (smallest distance from the sun)
  preferentially avoid Neptune. In fact, it is well
  known that Pluto's orbit crosses inside that of
  Neptune, but close encounters are always avoided.
  This property is also shared by a number of the
  known Plutinos (e.g. 1993 SB, 1994 TB, 1995 QY9),
  further enhancing the dynamical similarity with
  Pluto.

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Plutinos

• Approximately 1/4 of the known trans-Neptunian
  objects are Plutinos. A few more are suspected
  residents of other resonances (e.g. 1995 DA2 is
  probably in the 43). By extrapolating from the
  limited area of the sky so far examined, we have
  estimated that the number of Plutinos larger than
  100 km diameter is 1400, to within a factor of a
  few, corresponding to a few of the total. The
  number is uncertain for several reasons. First,
  the Plutinos are observationally over-assessed
  due to their being closer (brighter), on average,
  than the Classical KBOs giving rise to an
  observational bias in favor of the Plutinos. The
  intrinsic fraction is smaller than the actual
  fraction. Second, the initial orbits published by
  the IAU are little more than guesses, only weakly
  constrained by the limited orbital arcs. Pluto is
  distinguished from the Plutinos by its size it
  is the largest object identified to date in the
  32 resonance.

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Plutinos

• How did the 32 resonance come to be so full? An
  exciting idea has been explored by Renu Malhotra.
  Building on earlier work by Julio Fernandez, she
  supposes that, as a result of angular momentum
  exchange with planetesimals in the accretional
  stage of the solar system, the planets underwent
  radial migration with respect to the sun. Uranus
  and Neptune, in particular, ejected many comets
  towards the Oort Cloud, and as a result the sizes
  of their orbits changed. As Neptune moved
  outwards, its mean motion resonances were pushed
  through the surrounding planetesimal disk. They
  swept up objects in much the same way that a snow
  plough sweeps up snow. Malhotra has examined this
  process numerically, and finds that objects can
  indeed be trapped in resonances as Neptune moves,
  and that their eccentricities and inclinations
  are pumped during the process.

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Plutinos

• This scenario has the merit of being a natural
  consequence of angular momentum exchange with the
  planetesimals there is really no doubt that
  angular momentum exchange took place. However,
  some researchers are unsure whether Neptune moved
  out as opposed to in, and question the distance
  this planet might have moved. They also assert
  that the inclination of Pluto is larger than
  typical of the objects in Malhotra's simulations
  (and notice that the inclination of 1995 QZ9 is
  still larger than that of Pluto).

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Plutinos

• The dynamical situation is presently unclear, but
  the "moving planets" hypothesis appears as good
  as any, and better than most.
• A plot of the semi-major axes of the KBOs versus
  their orbital eccentricities clearly shows a
  non-random distribution. The Plutinos lie in a
  band at 39 AU, while most of the other KBOs are
  further from the sun. Solid blue points in this
  plot mark KBOs observed on 2 or more years. Their
  orbits are thought to be reasonably well
  determined. Unfilled circles mark KBOs observed
  only in one year. In some cases, these objects
  were recently discovered and we expect that they
  will be re-observed next year. In other cases,
  the KBOs have been lost. The upper diagonal line
  in the figure separates objects with perihelion
  inside Neptune's orbit (above the line) from the
  others. Note that Pluto (marked with an X) falls
  above the line. The lower diagonal line shows
  where objects have perihelion at 35 AU (i.e. 5 AU
  from Neptune's orbit). Note also that 1996 TL66
  and the other scattered KBOs are so far off scale
  that we have not included them in this plot. This
  plot is updated from a paper describing our 8k
  CCD observations of the Kuiper Belt (Jewitt, Luu
  Trujillo, 1998).

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Plutinos

• The inclinations of the well observed Plutinos
  range up to about 20 degrees (see also PS
  version, PDF version). This is in reasonable
  agreement with the inclinations expected from the
  migration hypothesis under plausible assumptions
  about the motion of Neptune. Some non-resonant
  KBOs have inclinations much higher than the
  Plutinos and this is a dynamical surprise, for
  which no clear explanation currently exists. We
  expect that resonance trapping should excite the
  inclinations of Plutinos, but there are no
  self-evident mechanisms by which the inclinations
  of Classical KBOs should be pumped.
• Dan Green has written a detailed opinion about
  the perceived status of Pluto in the era of the
  Kuiper Belt. It's worth a look.

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SCATTERED KUIPER BELT OBJECTS (SKBOs)

• Some KBOs possess large, eccentric, inclined
  orbits that have perihelion distances near q 35
  AU. The archetypal "Scattered Kuiper Belt Object"
  is 1996 TL66 , discovered as part of a 50 square
  degree survey using the University of Hawaii
  2.2-m telescope on Mauna Kea. In February 1999,
  we discovered 3 more examples of SKBOs (1999
  CV118, CY118 and CF119) in a deeper wide field
  survey undertaken with the Canada-France-Hawaii
  Telescope and a 12288x8192 pixel CCD. As our
  survey has progressed the number of SKBOs has
  risen dramatically, so that now we clearly see
  that that the SKBOs are a distinct dynamical
  population in the Kuiper Belt, separate from the
  Classical and Resonant objects. We expect that
  more SKBOs will be discovered as improved
  technology allows us to probe larger areas of the
  ecliptic sky to deeper limiting magnitudes.

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SCATTERED KUIPER BELT OBJECTS (SKBOs)

• Population
• The 35 AU perihelion distances allow Neptune to
  exert weak dynamical control over the SKBOs. On
  billion year timescales, perihelic perturbations
  by Neptune will change the orbit parameters from
  their present values. The SKBOs form a fat
  doughnut around the Classical and Resonant KBOs,
  extending to large distances. 1999 CF119 has an
  aphelion distance near 200 AU, showing that the
  SKBO doughnut extends to at least this distance.
  Eventually, much larger orbits will be found.
  There is, however, an important bias against
  finding SKBOs with very large aphelion distances.
  Such objects spend only a small fraction of each
  orbit close enough to the sun to be detected in
  ground-based observational surveys. 1999 CF119,
  for example, would be undetectable in the survey
  in which it was discovered for more than 90 of
  each orbit. This is why large sky areas must be
  studied in order to find SKBOs. In fact, SKBOs
  account for only 3 to 4 of the known Kuiper Belt
  Objects but, because of observational bias, this
  is a strong lower limit to the abundance of these
  objects. A list of SKBOs (unfortunately mixed in
  with the Centaurs) is maintained by the Minor
  Planet Center.

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SCATTERED KUIPER BELT OBJECTS (SKBOs)

• Origin
• How did the SKBOs get their eccentric, looping
  orbits? Fernandez (1980) suggested that
  planetesimals might be scattered into this type
  of orbit in the early days of the solar system.
  KBOs that approach Neptune closely are generally
  scattered away on short (million year)
  timescales. Many are passed to the dynamical
  control of other planets, ultimately to be lost
  from the solar system by ejection or by
  absorption (collision with a planet or the sun).
  Planetesimals ejected into very large orbits
  either escape from the gravitational influence of
  the sun (and then enter the realm of interstellar
  space) or may be perturbed by the galactic tidal
  field and by passing stars into orbits in the
  Oort Cloud. Objects scattered to the few 100 AU
  aphelion distances seen in the SKBOs are immune
  to galactic and stellar tides, and so remain in a
  tightly bound swarm (the fat doughnut)
  surrounding the solar system. Numerical
  simulations of this process by Duncan and Levison
  (1997) show this process in operation.

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SCATTERED KUIPER BELT OBJECTS (SKBOs)

• Source of Short-Period Comets
• The dynamical involvement with Neptune means that
  the SKBOs are a potential source of short-period
  comets. Occasional Neptune perturbations can
  deflect SKBOs to planet-crossing orbits. Some of
  these bodies may find their way to the inner
  solar system, where sublimation of embedded ices
  will lead to their classification as comets. In
  part because the SKBO population is very
  uncertain, the ratio of short-period comets
  delivered from the resonances to those from the
  scattered disk is highly uncertain.

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SEDNA

• Sedna was discovered as part of a continuing and
  highly productive survey lead by Mike Brown and
  Chad Trujillo, of Caltech and Gemini Observatory,
  respectively. The survey uses a wide-field
  telescope on Palomar Mountain to hunt for bright
  Kuiper Belt Objects (KBOs). The orbit has
  semimajor axis/eccentricity/inclination a/e/i
  532AU/0.857/11.9.

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Why is Sedna interesting?

• Its perihelion (closest approach to the Sun) is
  at 76 AU. This means that it is effectively
  beyond the scattering influence of Neptune. This
  is unlike the Classical KBOs, and unlike the
  Scattered KBOs. It is similar, dynamically, to
  2000 CR105 (for which a/e/i 227AU/0.805/22.7)
  which has perihelion at 44 AU, also outside
  Neptune's reach, and which has been discussed in
  papers by Gladman et al (Icarus 157, 269, 2002)
  and Emelyanenko et al (Monthly Notices RAS, 338,
  443, 2003). Other objects have larger aphelia
  than Sedna's 990 AU (e.g. Kuiper Belt Object 2000
  OO67, with aphelion at 1010 AU) and many comets
  travel to larger distances. Sedna is interesting
  because of its perihelion distance.

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Why is Sedna interesting?

• Sedna is large (1000 - 1500 km). An object this
  large cannot have formed by accretion in the
  tenuous regions of the protoplanetary disk
  corresponding to its current location. Sedna must
  have formed elsewhere, presumably amongst the
  planets or in the Kuiper Belt, and been ejected
  outwards. Lastly, its perihelion was lifted out
  of the range of Neptune.
• The orbit and the size attest to an early epoch
  in which strong gravitational scattering events
  rearranged the small bodies of the solar system.

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Is Sedna an Oort Cloud Comet?

• From the Classical Oort Cloud - no. The latter
  consists of objects whose orbits are so large
  (50,000 AU) that passing stars and galactic tides
  can alter their properties. Sedna doesn't travel
  very far out (1000 AU) and is effectively immune
  to external forces. Also, the inclinations of
  both Sedna and 2000 CR105 are small (12 and 23
  degrees, respectively). These objects know where
  the plane of the solar system lies. Oort Cloud
  orbits are random with inclinations all the way
  up to 180 degrees.

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• Sedna could be a member of a substantial
  population of bodies trapped between the Kuiper
  Belt and Oort Cloud. These would have been
  emplaced at early times and unseen until
  recently. 2000 CR105 and Sedna are "just the tip
  of the iceberg", as they say. The scientific
  interest lies in how these objects had their
  perihelia lifted out of the planetary region.

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• Is Sedna Planet X?No. Planet X is a term
  invoked by Percival Lowell in the beginning of
  the 20th Century, when he thought that a planet
  massive enough to perturb Neptune might exist at
  large distances. Sedna, although big relative to
  most other KBOs, is too puny to measurably
  perturb Neptune (or anything else for that
  matter). Its mass is roughly one thousandth that
  of the Earth.

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• Sedna 2003 VB12 is an exciting new object whose
  large perihelion distance - beyond the reach of
  Neptune - is nearly unique amongst Kuiper Belt
  Objects. It has probably followed a dynamical
  path different from those of most KBOs and
  different from the Classical Oort Cloud comets.
  Its large size indicates that it was formed
  closer to the Sun and scattered outwards,
  probably at early times.

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