Transcript The Kuiper Belt

Presents
The Kuiper Belt
The Kuiper Belt
In a previous session we learned about
the Oort Cloud. Today we will discuss the
Kuiper belt as an extension to our
discussion about the Oort cloud and our
solar system.
The Kuiper Belt
Most people think the Solar System ends with Pluto.
This is not the case. The asteroids - leftover material
from the formation of the solar system - between Mars
and Jupiter are not all that remains from that violent
time. Beyond the orbits of Neptune and Pluto lie a large
number of small, icy bodies, making up what is known
as the Kuiper Belt (pronounced Ki-per).
The Kuiper Belt
From 1992 onwards, astronomers began to discover
large numbers of these bodies orbiting beyond
Neptune, between 30-50 AU. At least 70,000 are known
with diameters above 100 km. The vast majority,
however, are between 10-50 km across, and so are
very dim indeed.
The Kuiper Belt
Due to their vast distance from the Sun, they
take hundreds of years to complete an
orbit, and move very slowly. For all these
reasons, detection is very difficult.
The Kuiper Belt
The Kuiper Belt is named after the
famous Dutch astronomer, Gerald
Kuiper [1905-73], who was a pioneer in
solar system research using spacecraft.
He put forward a new theory of how the
solar system was formed, and it is
generally accepted today. People had
believed that the planets had formed
from material hurled off from the Sun.
Kuiper argued that a gas and dust cloud
collapsed under gravity, forming the Sun
and planets separately.
The Kuiper Belt
In 1951 he suggested that short-period
comets (those coming from just beyond
Pluto) originate from a collection of
material left over from the formation. When
the first KBOs were discovered, after
Kuiper's death, the belt was named in his
honour.
The Kuiper Belt
Occasionally the orbit of a Kuiper Belt
object will be disturbed by the interactions
of the giant planets in such a way as to
cause the object to cross the orbit of
Neptune. It will then very likely have a
close encounter with Neptune sending it
out of the solar system or into an orbit
crossing those of the other giant planets or
even into the inner solar system.
The Kuiper Belt
There are presently nine known objects orbiting between
Jupiter and Neptune (including 2060 Chiron (aka 95
P/Chiron) and 5145 Pholus; see the MPC's list). The IAU
has designated this class of objects as Centaurs. These
orbits are not stable. These objects are almost certainly
"refugees" from the Kuiper Belt. Their future fate is not
known. Some of these show some cometary activity (ie,
their images are a little fuzzy indicating the presence of a
diffuse coma). The largest of these is Chiron which is
about 170 km in diameter, 20 times larger than Halley. If
it ever is perturbed into an orbit that approaches the Sun
it will be a truly spectacular comet.
The Kuiper Belt
Curiously, it seems that the Oort Cloud
objects were formed closer to the Sun
than the Kuiper Belt objects. Small objects
formed near the giant planets would have
been ejected from the solar system by
gravitational encounters. Those that didn't
escape entirely formed the distant Oort
Cloud. Small objects formed farther out
had no such interactions and remained as
the Kuiper Belt objects.
The Kuiper Belt
Several Kuiper Belt objects have been discovered
recently including 1992 QB1 and 1993 SC. They appear
to be small icy bodies similar to Pluto and Triton (but
smaller). There are more than 800 known transNeptunian objects (as of early 2004) Many orbit in 3:2
resonance with Neptune (as does Pluto). Color
measurements of some of the brightest have shown that
they are unusually red. In late 2002, a Kuiper Belt object
over 1000 km in diameter was discovered and
provisionally designated 2002 LM60 "Quaoar". In early
2004 an even larger one, 2004 DW, was found (its size
isn't well known yet, but it's almost certainly smaller than
Pluto).
The Kuiper Belt
It is estimated that there are at least
35,000 Kuiper Belt objects greater than
100 km in diameter, which is several
hundred times the number (and mass) of
similar sized objects in the main asteroid
belt.
The Kuiper Belt
•
Breaking News
On March 15, 2004, a team of astronomers (including Mike Brown, Chad
Trujillo, and David Rabinowitz) announced the NASA-sponsored discovery of a
very large planetary body (originally designated 2003 VB12) in one of the most
distant planetary orbits yet discovered within the Solar System. Confirmed by
the Spitzer (infrared) Space Telescope and tentatively named Sedna after the
Inuit Goddess of the Sea (from which all creatures of the very cold Arctic sea
were created), it is currently located around 90 AUs from our Sun, Sol -- an
orbital distance that is roughly three times farther out than that of Pluto or
Neptune -- but will eventually move as much as 10 times farther away (around
990 AUs) in a 12,260-year orbit around Sol; it's orbital semi-major axis is
around 532 AUs with an extremely high eccentricity of 0.857. Based on its
current distance, brightness, and presumed albedo or ability to reflect light,
Sedna has been estimated to have more than half the diameter of Pluto and
may be larger than any other planetary body found since Pluto -- at 730 to 1,470
miles or 1,180 to 2,360 kilometers (km) across, compared to Pluto's diameter of
around 1,440 miles or 2,320 km.
The Kuiper Belt
Although inclined by only around 11.9 degrees from the
ecliptic where the eight major planets orbit, Sedna's
distant orbit is extremely elliptical indicating that its
formation and orbit may have been influenced by by a
passing nearby star during the early years of the Solar
System, when Sol formed out of a molecular cloud with
many other closeby stars around 4.6 billion years ago.
Like 2000 CR105, Sedna may have been perturbed by a
Solar-mass star at around 800 AUs from Sol more than
100 million years after its birth, given today's observed
numbers of Oort Cloud comets. Hence, 2000 CR105 and
Sedna are less likely to be members of the scattered
disk that had their perihelion distances "increased by
chaotic diffusion" or the result of other hypotheses
(Morbidelli and Levison, submitted 2004).
The Kuiper Belt
Sedna is the second most reddish planetary body in the
Solar System, after Mars. Although an apparently slow
rotation (40 days) indicated that Sedna might have its
own moon, astronomers were unable to find such an
object with the Hubble Space Telescope (more
information and images from NASA). The icy object will
move closer to the Sun over the next 72 years -- to 76
AUs of Sol -- before receding back towards the inner
Oort Cloud (more information and images can be found
from the NASA press release, Spitzer press release,
astronomer Mike Brown's Sedna Page, Astronomy
Picture of the Day, and the Kuiper Belt Page).
The Kuiper Belt
On February 17, 2004, astronomers at the California Institute of
Technology and (Caltech) Yale University announced that they may
have found the largest Edgeworth-Kuiper Belt object, designated 2004
DW, since the discovery of Pluto on February 18, 1930. Based on its
current distance of around 48 AUs from Sol, brightness, and presumed
albedo or ability to reflect light, 2004 DW has been estimated to be
around 870 to 990 miles (1,400 to 1,600 kilometers) across, or more
than half the size of Pluto. Preliminary orbital characteristics have
been determined using images of the object traced back to a First
Palomar Sky Survey photograph of November 23, 1954 and to a
November 8, 1951 photograph by Australia's Siding Spring
Observatory. Suggesting a striking similarity to Pluto and membership
to a class of objects called Plutinos, 2004 DW's orbital distance from
the Sol varies between 30.9 and 48.1 AUs with an orbital inclination of
about 20.6°, which is larger even than that of Pluto -- which is itself far
larger than that any other planet in the Solar System. 2004 DW takes
248 years to complete its orbit. It reached its farthest point from the
Sun in 1989 and so is now moving inbound towards Sol, reaching
perihelion in 2113.