Download Kuiper Belt, Oort Cloud and TNOs

Kuiper Belt,
Oort Cloud and TNOs
Planetologie II UE SS2011
Gerhard Weihs
Gerhard Weihs: „Kuiper Belt, Oort Cloud and TNOs “
Planetologie II UE SS2011
Folie 1
16.05.2011
Content
• Small Solar System body (SSSB)
• Short history
• TNOs (Trans-Neptunian Objects)
• Kuiper belt (engl. Edgeworth-Kuiper belt )
• scattered disk
• Oort cloud
• Forming (NICE-model of migration)
Gerhard Weihs: „Kuiper Belt, Oort Cloud and TNOs “
Planetologie II UE SS2011
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Small Solar System body (SSSB)
Definition of SSSB
IAU 2006 describes objects in the Solar System that are neither
planets nor dwarf planets, nor satellites of a planet or dwarf planet:
All other objects orbiting the Sun shall be referred to collectively as
"Small Solar System Bodies" ... These currently include most of the
Solar System asteroids, most Trans-Neptunian Objects (TNOs),
comets, and other small bodies.[1]
* the classical asteroids, with the exception of Ceres;
* the centaurs and trojans;
* the Trans-Neptunian Objects, with the exception of Pluto,
Haumea, Makemake and Eris;
* all comets.
Gerhard Weihs: „Kuiper Belt, Oort Cloud and TNOs “
Planetologie II UE SS2011
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short history
Significant Dates
1943: Astronomer Kenneth Edgeworth suggests that a reservoir of comets and
larger bodies resides beyond the planets.
1950: Astronomer Jan Oort theorizes that a vast population of comets may exist in a
huge cloud on the distant edges of our solar system.
1951: Astronomer Gerard Kuiper predicts the existence of a belt of icy objects just
beyond the orbit of Neptune.
1992: After five years of searching, astronomers David Jewitt and Jane Luu discover
the first KBO, 1992QB1.
2002: Scientists using the 48-inch Oschin telescope at Palomar Observatory find
Quaoar, the first large KBO hundreds of kilometers in diameter. This object
was photographed in 1980, but was not noticed in those images.
2004: Astronomers using the 48-inch Oschin telescope announce the discovery of
Sedna (2003VB12).
2005: Astronomers announce the discovery of 2003UB313. This object, later named
Eris, is slightly larger than Pluto.
2008: The Kuiper Belt object provisionally known as 2005FY9 ("Easterbunny") is
recognized in July as a dwarf planet and named Makemake (pronounced
MAHkeh-MAHkeh) after the Polynesian (Rapa Nui) creation god. In September
2003EL61 ("Santa") was designated a dwarf planet and given the name
Haumea after the Hawaiian goddess of fertility and childbirth.
Gerhard Weihs: „Kuiper Belt, Oort Cloud and TNOs “
Planetologie II UE SS2011
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TNOs (Trans-Neptunian Objects)
TNOs
are classified in two large groups, according to their distance
from the Sun and their orbit parameters, :
• Kuiper belt (engl. Edgeworth-Kuiper belt )
• Scattered disk
Gerhard Weihs: „Kuiper Belt, Oort Cloud and TNOs “
Planetologie II UE SS2011
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16.05.2011
Kuiper belt
• a torus-shaped region called Edgeworth-Kuiper belt too
• contains objects usually having close-to-circular orbits with a
small inclination from the ecliptic
• extending from the orbit of Neptune at 30 AU to 55 AU
• consists mainly of small bodies, or remnants from the Solar
System's formation
• The belt is home to at least four dwarf planets – Pluto,
Haumea, Eris and Makemake – called „plutinos“
• The belt ist home of short-range comets
Gerhard Weihs: „Kuiper Belt, Oort Cloud and TNOs “
Planetologie II UE SS2011
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Scattered disk
Scattered disk contains objects further from the Sun
• average distance from 55 to about 100 AU
• usually with very irregular orbits (i.e. very elliptical and having
a strong inclination from the ecliptic).
• A typical example is the most massive known TNO - Eris.
• The belt ist home of short-range comets
Gerhard Weihs: „Kuiper Belt, Oort Cloud and TNOs “
Planetologie II UE SS2011
Folie 7
16.05.2011
Kuiper belt objects (KBOs)
Kuiper belt objects (KBOs) are composed largely of frozen
volatiles (termed "ices"), such as methane, ammonia and water.
• They are further classified into the following two groups:
• Resonant objects are locked in an orbital resonance with
Neptune.
- Objects with a 1:2 resonance are also called twotinos,
and
- objects with a 2:3 resonance are called plutinos, after
their most prominent member, Pluto.
• Classical Kuiper belt objects (also called cubewanos,
CKBOs)) have no such resonance, moving on almost
circular orbits, unperturbed by Neptune.
- Examples are 1992 QB1, 50000 Quaoar and Makemake.
Gerhard Weihs: „Kuiper Belt, Oort Cloud and TNOs “
Planetologie II UE SS2011
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Trans-Neptunian objects (TNOs)
Gerhard Weihs: „Kuiper Belt, Oort Cloud and TNOs “
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Trans-Neptunian objects (TNOs)
Gerhard Weihs: „Kuiper Belt, Oort Cloud and TNOs “
Planetologie II UE SS2011
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Largest Trans-Neptunian Objects
Gerhard Weihs: „Kuiper Belt, Oort Cloud and TNOs “
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Groups
Centaurs (no TNO)
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•
an object is classified as a centaur if its semi-major axis lies
between Jupiter and Neptune
There is no clear orbital distinction between centaurs and comets.
Plutinos similar orbits as Pluto
Kuiper Belt
Scattered disk
Gerhard Weihs: „Kuiper Belt, Oort Cloud and TNOs “
Planetologie II UE SS2011
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Colours of TNOs
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Planetologie II UE SS2011
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Physical characteristics of TNOs
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•
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Studying colors and spectra provides insight into the objects' origin
and a potential correlation with other classes of objects, namely
centaurs and some satellites of giant planets (Triton, Phoebe),
suspected to originate in the Kuiper Belt.
the interpretations are ambiguous as the optical surfaces of small
bodies are subject to modification by intense radiation, solar wind
and micrometeorites
Consequently, the thin optical surface layer could be quite different
from the regolith underneath
Small TNOs are thought to be low density mixtures of rock and ice
with some organic (carbon-containing) surface material such as
tholin, detected in their spectra.
On the other hand, the high density of Haumea, 2.6-3.3 g/cm3,
suggests a very high non-ice content (compare with Pluto's density:
2.0 g/cm3).
The composition of some small TNO is similar to that of comets.
Some Centaurs undergo seasonal changes when approaching the Sun
Gerhard Weihs: „Kuiper Belt, Oort Cloud and TNOs “
Planetologie II UE SS2011
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Other properties of TNOs
Gerhard Weihs: „Kuiper Belt, Oort Cloud and TNOs “
Planetologie II UE SS2011
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Oort Cloud
• The Oort cloud is a hypothesized spherical cloud of comets
which is thought to occupy a vast space from between 2,000 or
5,000 AU (0.03 and 0.08 ly) to about 50,000 AU (0.79 ly) from
the Sun.
• The outer extent of the Oort cloud defines the gravitational
boundary of our Solar System.
• The Oort cloud is thought to comprise two separate regions a spherical outer Oort cloud and a disc-shaped inner Oort
cloud, or Hill cloud.
• Objects in the Oort cloud are largely composed of ices, such
as water, ammonia, and methane.
• the Oort cloud was 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.
Gerhard Weihs: „Kuiper Belt, Oort Cloud and TNOs “
Planetologie II UE SS2011
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Oort Cloud
• A cloud population of 1.4 trillion comets brighter than an
absolute magnitude of 11
• The total mass of comets in the Oort cloud is calculated
according to a derived relationship between brightness and
nucleus mass.
• The estimated total mass is 1.9 earth masses. The probable
error in the estimate is about one order of magnitude.
• Most of the mass of the Oort cloud is concentrated in the size
range of the observed long-period comets.
Gerhard Weihs: „Kuiper Belt, Oort Cloud and TNOs “
Planetologie II UE SS2011
Folie 17
16.05.2011
Oort Cloud
Gerhard Weihs: „Kuiper Belt, Oort Cloud and TNOs “
Planetologie II UE SS2011
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Kuiper Belt, Oort Cloud
Gerhard Weihs: „Kuiper Belt, Oort Cloud and TNOs “
Planetologie II UE SS2011
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Origin of comets
• Short-period comets (those with orbits of up to 200 years)
are generally accepted to have emerged from the Kuiper belt or
scattered disk
• Comets pass from the scattered disc into the realm of the
outer planets, becoming what are known as centaurs.
These centaurs are then sent farther inward to become the
short-period comets.
• There are two main varieties of short-period comet: Jupiterfamily comets (those with semi-major axes of less than 5
AU) and Halley-family comets.
• Long-period comets, such as comet Hale-Bopp, whose orbits
last for thousands of years, are thought to originate in the Oort
cloud.
Gerhard Weihs: „Kuiper Belt, Oort Cloud and TNOs “
Planetologie II UE SS2011
Folie 20
16.05.2011
Oort cloud as source of comets
• Oort cloud 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.
Gerhard Weihs: „Kuiper Belt, Oort Cloud and TNOs “
Planetologie II UE SS2011
Folie 21
16.05.2011
cometary fading
• Oort noted that the number of returning comets was far less
than his model predicted, and this issue, known as "cometary
fading", has yet to be resolved.
• No known dynamical process can explain this undercount of
observed comets. Hypotheses for this discrepancy include
the destruction of comets due to tidal stresses, impact or
heating; the loss of all volatiles, rendering some comets
invisible, or the formation of a non-volatile crust on the
surface.
• Dynamical studies of Oort Cloud comets have shown that
their occurrence in the outer planet region is several times
higher than in the inner planet region. This discrepancy may
be due to the gravitational attraction of Jupiter, which acts as
a kind of barrier, trapping incoming comets and causing
them to collide with it, just as it did with Comet ShoemakerLevy 9 in 1994.
Gerhard Weihs: „Kuiper Belt, Oort Cloud and TNOs “
Planetologie II UE SS2011
Folie 22
16.05.2011
NICE – model of planetary migration
The Nice model is a scenario for the dynamical evolution of
the Solar System. It is named for the location of the
Observatoire de la Côte d'Azur, where it was initially developed,
in Nice, France (2005):
•
It proposes the migration of the giant planets from an
initial compact configuration into their present positions
• This planetary migration is used to explain:
-
the Late Heavy Bombardment of the inner Solar System,
the forming of the Oort cloud, and the
existence of small Solar System bodies including
the forming of the Kuiper belt and scattered disk,
the Neptune and Jupiter Trojans, and
the numerous resonant trans-Neptunian objects dominated
by Neptune.
Gerhard Weihs: „Kuiper Belt, Oort Cloud and TNOs “
Planetologie II UE SS2011
Folie 23
16.05.2011
NICE – model of planetary migration
Proposals:
• The NICE model proposes that after the dissipation of the gas
and dust of the primordial Solar System disk, the four giant
planets (Jupiter, Saturn, Uranus and Neptune) were originally
found on near-circular orbits between ~5.5 and ~17 AU, much
more closely spaced and more compact than in the present.
• A large, dense disk of small, rock and ice planetesimals,
their total about 35 Earth masses, and extended from the orbit
of the outermost giant planet to some 35 AU.
Gerhard Weihs: „Kuiper Belt, Oort Cloud and TNOs “
Planetologie II UE SS2011
Folie 24
16.05.2011
NICE – model of planetary migration
Migration:
• Planetesimals at the disk's inner edge occasionally pass through
gravitational encounters with the outermost giant planet, which
change the planetesimals' orbits.
• The planets scatter inwards the majority of the small icy bodies that
they encounter, exchanging angular momentum with the scattered
objects so that the planets move outwards in response, preserving
the angular momentum of the system.
• These planetesimals then similarly scatter off the next planet they
encounter, successively moving the orbits of Uranus, Neptune, and
Saturn outwards.
• This process continues until the planetesimals interact with the
inmost and most massive giant planet, Jupiter, whose immense gravity
sends them into highly elliptical orbits or even ejects them outright
from the Solar System.
• This, in contrast, causes Jupiter to move slightly inward
Gerhard Weihs: „Kuiper Belt, Oort Cloud and TNOs “
Planetologie II UE SS2011
Folie 25
16.05.2011
NICE – model of planetary migration
Forming of Kuiper Belt and Oort Cloud:
• objects scattered by Jupiter into highly elliptical orbits formed
the Oort cloud;
• objects scattered to a lesser degree by the migrating Neptune
formed the current Kuiper belt and scattered disc.
• This scenario explains the Kuiper belt's and scattered disc's
present low mass.
• Some of the scattered objects, including Pluto, became
gravitationally tied to Neptune's orbit, forcing them into meanmotion resonances.
• Eventually, friction within the planetesimal disc made the orbits of
Uranus and Neptune circular again.
• In contrast to the outer planets, the inner planets are not
believed to have migrated significantly over the age of the Solar
System, because their orbits have remained stable following the
period of giant impacts.
Gerhard Weihs: „Kuiper Belt, Oort Cloud and TNOs “
Planetologie II UE SS2011
Folie 26
16.05.2011
References
Wikipedia
„Comets: Coming inside from the Cold“
„Ice Worlds at the Outer Limit“
ESO Messenger 141-Sep 2010, 15-19
Gerhard Weihs: „Kuiper Belt, Oort Cloud and TNOs “
Planetologie II UE SS2011
Folie 27
16.05.2011