Transcript Pluto and the Kuiper Belt Objects

Pluto and the Kuiper Belt Objects (KBOs)
The IAU draft definition of "planet" and
"plutons"
Q: What is a “double planet”?
A: A pair of objects, which each independently satisfy the definition of “planet” are considered a
“double planet” if they orbit each other around a common point in space that is technically known
as the “barycentre”. In addition, the definition of “double planet” requires that this “barycentre”
point must not be located within the interior of either body.
Q: What is a “satellite” of a planet?
A: For a body that is large enough (massive enough) to satisfy the definition of “planet”, an object
in orbit around the planet is called a “satellite” of the planet if the point that represents their
common centre of gravity (called the “barycentre”) is located inside the surface of the planet.
Q: The Earth’s moon is spherical. Is the Moon now eligible to be called a “planet”?
A: No. The Moon is a satellite of the Earth. The reason the Moon is called a “satellite” instead of a
“planet” is because the common centre of gravity between the Earth and Moon (called the
“barycentre”) resides below the surface of the Earth.
Q: Why is Pluto-Charon a “double dwarf planet” and not a “dwarf planet with a satellite”?
A: Both Pluto and Charon each are large enough (massive enough) to be spherical. Both bodies
independently satisfy the definition of “dwarf planet”. The reason they are called a “double dwarf
planet” is that their common centre of gravity is a point that is located in free space outside the
surface of Pluto. Because both conditions are met: each body is “planet-like” and each body orbits
around a point in free space that is not inside one of them, the system qualifies to be called a
“double dwarf planet.”
RESOLUTIONS 5 and 6
Definition of a Planet in the Solar System and Pluto
Contemporary observations are changing our understanding of planetary systems, and it is important that our
nomenclature for objects reflect our current understanding. This applies, in particular, to the designation
"planets". The word "planet" originally described "wanderers" that were known only as moving lights in the sky.
Recent discoveries lead us to create a new definition, which we can make using currently available scientific
information.
The IAU therefore resolves that planets and other bodies, except satellites, in our Solar System be defined into
three distinct categories in the following way:
(1) A planet is a celestial body that
(a) is in orbit around the Sun,
(b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic
equilibrium (nearly round) shape, and
(c) has cleared the neighborhood around its orbit.
(2) A "dwarf planet" is a celestial body that
(a) is in orbit around the Sun,
(b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic
equilibrium (nearly round) shape,
(c) has not cleared the neighborhood around its orbit, and
(d) is not a satellite.
(3) All other objects, except satellites, orbiting the Sun shall be referred to collectively as "Small Solar System
Bodies".
The IAU further resolves: Pluto is a "dwarf planet" by the above definition and is recognized as the prototype of a
new category of Trans-Neptunian Objects.
1. The eight planets are: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune.
2. An IAU process will be established to assign borderline objects into either dwarf planet and other categories.
3. These currently include most of the Solar System asteroids, most Trans-Neptunian Objects (TNOs), comets, and
other small bodies.
About 1.900 g/cm3
Pluto
Discovered 1930 by C. Tombaugh.
Existence predicted from orbital disturbances of Neptune, but Pluto
is actually too small to cause those disturbances.
Pluto and its moon, Charon, may be typical of a
thousand icy objects that orbit far from the Sun
• Pluto was discovered after a long search
• Pluto and its moon, Charon, move together in a highly
elliptical orbit steeply inclined to the plane of the ecliptic
• They are the only worlds in the solar system not yet
visited by spacecraft
The Discovery of Pluto
Pluto’s orbit is eccentric and inclined to the
plane of the ecliptic; it also crosses the orbit of
Neptune:
The Physical Properties of Pluto
Its orbit is at a large angle to the plane of
Pluto’s orbit:
Pluto
Virtually no surface
features visible from Earth.
~ 65 % of size of Earth’s
Moon.
Highly elliptical orbit;
coming occasionally closer
to the sun than Neptune.
Orbit highly inclined (17o)
against other planets’ orbits
 Neptune and Pluto
will never collide.
Surface covered with nitrogen ice; traces of frozen methane
and carbon monoxide.
Daytime temperature (50 K) enough to vaporize some N
and CO to form a very tenuous atmosphere.
Pluto and Charon
From separation and orbital period:
Mpluto ~ 0.2 Earth masses.
Density ≈ 2 g/cm3
(both Pluto and Charon)
 ~ 35 % ice and 65 % rock.
Large orbital inclinations 
Large seasonal changes on
Pluto and Charon.
The Physical Properties of Pluto
Pluto’s moon, Charon, was
discovered in 1978.
It is tidally locked to Pluto,
about half the size, and
1/12 the mass of Pluto
itself.
2 New Moons for Pluto!
• The candidate moons are approximately
27,000 miles (44,000 kilometers) away from
Pluto--in other words, two to three times as far
from Pluto as Charon.
• These are tiny moons. Their estimated
diameters lie between 40 and 125 miles (64
and 200 kilometers). Charon, for comparison,
is about 730 miles (1170 km) wide, while Pluto
itself has a diameter of about 1410 miles
(2270 km).
Pluto and its moons?
Pluto and its moons
The Origin of Pluto and Charon
Probably very different history than neighboring Jovian planets.
Older theory:
Pluto and Charon formed as moons of Neptune,
ejected by interaction with massive planetesimal.
Mostly abandoned today since
such interactions are unlikely.
Modern theory: Pluto and Charon
members of Kuiper belt of small,
icy objects.
Collision between Pluto and Charon may have caused the peculiar
orbital patterns and large inclination of Pluto’s rotation axis.
• Several hundred small, icy worlds have been
discovered beyond Neptune
• Pluto and Charon are part of this population
Kuiper Belt Objects
•
Several hundred small, icy worlds have been
discovered beyond Neptune
1. Classical Kuiper Belt Objects (CKBO)
– Orbits far from Neptune
2. Scattered Kuiper Belt Objects (SKBO)
– Come close enough to Neptune to be influenced (at least
once every billion years)
3. Plutinos
– In a 3:2 resonant orbit with Neptune. Just like Pluto! (more
than 15 at present)
•
For more info on KBOs try:
http://www.ifa.hawaii.edu/~jewitt/kb.html
Quaoar
CKBO
Sedna
An Oddity! Beyond even the SKBO!
Ixion
Chaos
Permanent
Designation
Provisional
Absolute
magnitude
Albedo
Designation
−1.0
Pluto
2005 FY9
2003 EL61
Charon
Equatorial
diameter
Semimajor
axis
(km)
(AU)
0.6
2320
39.4
Date
found
Discoverer
Diameter method
1930
C. Tombaugh
occultation
assumed albedo
0.6
(assumed)
~1900
45.7
2005
M. Brown, C. Trujillo
& D.
Rabinowitz
0.1
0.6 (assumed)
~1600
43.3
2005
J.L. Ortiz et al.
assumed albedo
1
0.4
39.4
1978
J. Christy
occultation
assumed albedo
−0.2
1205
(90482)
Orcus
2004 DW
2.3
0.1 (assumed)
~1500
39.4
2004
M. Brown, C. Trujillo
& D.
Rabinowitz
(50000)
Quaoar
2002 LM60
2.6
0.10 ± 0.03
1260 ± 190
43.5
2002
C. Trujillo & M. Brown
disk resolved
(28978) Ixion
2001 KX76
3.2
0.25 – 0.50
400 – 550
39.6
2001
Deep Ecliptic
Survey
thermal
2002 TX300
3.3
> 0.19
< 709
43.1
2002
NEAT
thermal
55636
C. Trujillo, M. Brown,
E. Helin, S.
Pravdo,
55565
2002 AW197
3.3
0.14 – 0.20
650 – 750
47.4
2002
K. Lawrence & M.
Hicks /
Palomar
Observatory
55637
2002 UX25
3.6
0.08?
~910
42.5
2002
A. Descour /
Spacewatch
assumed albedo
2000 WR106
3.7
0.12 – 0.30
450 – 750
43
2000
R. McMillan
thermal
2002 MS4
3.8
0.1 (assumed)
730?
41.8
assumed albedo
2003 AZ84
3.9
0.1 (assumed)
700?
39.6
assumed albedo
(20000)
Varuna
thermal