Astronomy Test 3

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Planetisimal

Back 1

During the planet-building process, the bodies which dominate the second to last
phase of material accumulation. During the planetisimal phase, millions of small bodies ranging in
size from a few miles to a few hundred miles across collide and merge building the planetary
embryos. Most of the minor planets are residual planetisimals from this phase of solar system
history

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Planetary Embryo

Back 2

During the planet-building process, the bodies which dominate last phase of
planet construction. Planetary embryo mergers occur at the stage where many hundreds of small
planets accrete into planets. The mergers at this point tend be quite violent and the final impacts can
leave lasting imprints are the planetary system

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Accretion

Back 3

A process of material accumulation and concentration. As the proto-stellar cloud
condensed and contracted it collected material into larger and larger structures through the process of
accretion. Black holes and white dwarf stars with red giant companions also have disks of
accumulated material orbiting around their equatorial regions referred to as accretion disks.

Front 4

Differentiation

Back 4

The separation and isolation of materials in a molten or slightly molten body due
to differences of density. The denser materials sink and the lighter materials float.

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Volcanism

Back 5

Geologic activity surrounding the venting of pressure and material (rock, dust, ash,
molten rock) from the mantle of a planetary body through its lithosphere. Vented mantle material is
known as magma or as lava when it flows across the surface.

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lunar mare

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The dark regions of the Moon that are ancient craters filled in by lava flows from
beneath an impact site. These large impacts broke through the young crust of the Moon while it still
had a molten core and the impact basins were filled in with large basaltic flows from within the
Moon. These are considered lowlands relative the brighter (more reflective, mountainous) highland
regions. There are very few maria on the far side of the Moon.

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crater

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An astrobleme or impact site on a planetary body. Volcanic vents can also take the form of
craters. Typically circular in nature they are the artifacts of collisions between small and large
bodies in the solar system. Craters cover all size ranges imaginable from a few centimeters to
hundreds of miles

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length to build a planet

Back 8

The only disagreement on this topic among astronomers is concerning the time period that the entire
planet building process takes. All agree that at least 10 million years are necessary, but by 100
million years the entire process is complete

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co formation moon theory

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Co-formation (sister planet) had been a popular theory before the manned moon landings, but the
lack of an iron core similar to earth's core has ruled that theory out. If the moon formed with the
earth it would have formed from essentially the same materials in the same distributions and would
have an identical chemical signature. The moon's lack of an iron core is a major obstacle to this
theory.

Front 10

similiarites of earth and moon

Back 10

Isotopes of oxygen are identical in both the earth's material and the moon rocks brought back by the
Apollo astronauts. Distributions of aluminum, silicon and magnesium have basically the same
ratios in the earth's mantle as in the moon's basalts.
The earth's core consists of a large accumulation of differentiated iron and nickel. The moon's core
is very, very small and contains a small amount iron and nickel. As a result the moon's overall
density is only 3.3 g/cc compared to the earth's 5.5 g/cc. The moon's large size relative to the earth
is difficult to explain in any model of moon formation.

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moon formed elsewhere in the solar system theory

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If the moon formed elsewhere and was captured by the earth, the shape and energy in the moon's
orbit would be radically different. The chemical composition would also be more varied from that
of the earth. Oxygen isotopes in rocks sampled from Mars and meteorites from elsewhere in the
solar system have different isotope ratios. The moon has identical oxygen isotope ratios to the earth
as proven by the Apollo moon rocks. The moon had to have formed from the same material that
formed the earth's mantle, but not the earth's core.

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spin theory

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Another theory held that the earth spun the moon's material off due to an excessive rotation rate.
This theory also would have the moon's orbit be radically different than what we observe. The
amount of excess rotational angular momentum would had to have been enormous and would had to
have occurred very early in the process before all of earth's iron had sunk to its center. If true, this
theory would support this event happening to most planets in the solar system. Only the earth has
such a massive moon. Any theory that suggests an evolutionary process of moon formation would
have deal with the issue that the same evolution would happen to other planets as well as the earth.

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current theory

Back 13

Current theories developed in the 1970's and 1980's about the formation of the moon support the
idea that the earth received a single glancing impact from a large planetary embryo late in the planet
building process. By the time of the impact, the earth's core had differentiated and the glancing blow
swept out mostly mantle material and imparted it with enough velocity to orbit the earth but not
escape the gravitational pull of the earth. Initially this material would form a substantial ring system
around the earth. Most of the impactor material, especially its core, did not maintain enough orbital
energy to continue in orbit around the sun. Any material not accelerated to a high enough velocity
would fall back and be incorporated into the reconstituted earth. Over a relatively short period of
time (300,000 years), the moon would solidify and clear out any ring system that would have formed
around the earth.

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uniqueness of earths moon

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It is unique in the sense that the mass of the
moon is extremely large as a ratio of the mass of the planet around which it orbits. The moon's mass
is about 1.2 % of the mass of the Earth. The very largest of the ratios of moon to planet masses of
other moons in the solar system are on the order of 1/100th of 1%.

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moons in the solar system

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All of the planets have one or more moons except for Venus and Mercury. Their small semi-major
axis and thus their high orbital velocities make moon formation or capture very improbable. There
are currently over 160 identified moons orbiting around the planets in the solar system and more are
being discovered all the time.

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embryo-sized moons

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Examining the inventory of Planetary moons we see that there really are 2 distinct sizings within the
moon population. The largest of these, what we can call embryo moons, or at least embryo-sized
moons are all near the same size as our moon (within a factor of 2). There are 7 of these large
moons around the Solar System, most associated with Jupiter. The four Galilean Moons, the largest
moons orbiting Jupiter, were discovered by Galileo in 1610 just a few months after pointing his
telescope at the heavens. All four of these moons are embryo-sized and are bright enough that they
could be seen by the naked eye if Jupiter were not present. Titan, the single embryo-sized moon of
Saturn, was discovered in 1655 by Christiaan Huygens. Triton, the largest satellite of Neptune was
discovered by Lassell just a few weeks after the discovery of Neptune itself. The only other
embryo-sized moon in the solar system is our own Luna, discovered in antiquity

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triton

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There is no doubt that Triton, Neptune's big moon, formed independently of Neptune
and was captured long after the formation of the planets (+500 million years?). The largest piece of
evidence comes from its orbital period (see table below). You will note that the orbital period is
negative, indicating that it has a retrograde orbit. It orbits Neptune going the wrong way! Triton
also has a fairly inclined orbit; 130 degrees relative to the Ecliptic plane and 157 degrees relative to
Neptune's rotation. Because of it's retrograde orbit, Triton loses much orbital energy to Neptune due
to tidal interactions and its orbit is slowly decaying (rapidly in an Astronomical sense). In less than
half a billion years Triton will pass inside of Neptune's Roche limit and be torn apart, forming a
massive ring system dwarfing Saturn's current ring system. Triton may be the smallest of the
embryo-sized moons, but it is perhaps the only true Embryo Moon.

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other non-embryo moons

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The other moons of the Solar System are all relatively small, more akin to planetisimals in their size
and probably all are captured objects. Almost half have retrograde orbits (a sure sign of capture),
most have very eccentric orbits (a sign of recent capture; 1 to 3 billion years ago), and some have
very large orbits taking an earth-year or more to complete one orbit of the planet.

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Phobos and Deimos

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The very tiniest planetary moons in the Solar System belong to Mars; Phobos and Deimos. They are
only 7 miles and 12 miles across and are most probably captured objects from the nearby Asteroid
Belts. Note the orbital period of Phobos is .3 days, less than one sidereal period for Mars. This
means that Phobos orbits Mars (8 hours) faster than Mars rotates (25 hours). Think of the Diurnal
motion of the Moon seen here from Earth (westward) and its Orbital motion (eastward). The
Diurnal motion is much faster than the Orbital motion, so the Moon moves through the sky toward
the west. It rises in the East and sets in the West. Phobos' Diurnal motion (as seen from Mars) is
slower than its Orbital motion, so it moves through the sky to the East. It rises in the West and sets
in the East! This also places it closer to Mars than the radius of the Martian equivalent of a GeoSynchronous orbit (Arei-synchronous)

Front 20

formation of ring systems

Back 20

The more massive planets in the solar system have collected various
chunks of debris from the solar system and gravitationally captured this material into stable as well
as chaotic orbits. Most of these captured moons have rather eccentric orbit shapes as well as
osculating orbit parameters of a slightly more extreme nature than their host planets. Very small
debris will collect inside of a certain tidal energy orbit called the Roche Limit and the orbits becomevery homogeneous, very circularized, and highly concentrated in the equatorial region of a planet.
We see this material as structures; as rings around the planet.

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the roche limit

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The Roche Limit, calculated in 1848 by Edouard Roche, identifies a distance from a planet, where
an object of a particular density becomes tidally unstable and would be torn apart. The classical
value assumes a density of 1 gram per cubic centimeter, the same as the density of water.

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roche limit (more)

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The
density of the planet also plays a role in determining the altitude, within which, a body is materially
unstable. The inside (closest to the planet) surface of a "moonlet" receives an orbital acceleration
significantly greater than the acceleration felt by the outside surface. The body wants to orbit at two
different velocities and it is stretched apart by the disparate forces. If it does not contain a robust
enough internal structure (density), it will disintegrate into material of smaller proportions. The
material will lose orbital energy to the planet and slowly spiral in to the planet. The rings of the
Jovian planets are collections of this class of material.

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roche limite (continued)

Back 23

The typical density of the Jovian planets (1 to 2 gm/cc) is slightly denser, but very similar to that of
water. The second term of the formula calculates to a value very close to 1; the density ratio fraction
is a value not much larger than one, and the cube root of such a value is even closer to one. For
general application the value of the classical Roche Limit is 2.44 planet radii. All (but one) of the
ring systems around the planets are within the Roche Limit for their host planet.

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minor planet group

Back 24

A collection of minor planets designated by a shared or similar set of orbital
parameters. Most groups are designated by similar semi-major axis, but eccentricities and
inclinations can also specified. The “group” is usually named after the first minor planet discovered
of the set.

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minor planet family

Back 25

A collection of minor planets designated by a shared or similar set of orbital
parameters as well as chemical composition. It is presumed that the “family” originated by a single
parent body, which was broken up by earlier collisions. The “family” is usually named after the first
minor planet discovered of the set.

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hirayama group

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The same as a Minor Planet Group or Minor Planet Family derived from the
analysis techniques first used by Kiyotsugu Hirayama in 1918. Although Hirayama only identified
about 5 groups many more have been detected.

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Asteroid

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: A minor planet, usually interpreted as one of the minor planets located between the orbit
of Mars and Jupiter. In reality, asteroids (minor planets) are located throughout the entire solar
system.

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LaGrange Points

Back 28

In pure two body orbital systems, there are 5 points of stability that are created
by the interaction of the gravitational fields of the two bodies in the system. The 5 points are labeled
L1 through L5. L1 exists between the two bodies where the gravitational attraction of the two
bodies is at equilibrium. L2 is on a line that passes between the two bodies, but lies just outside the
smaller of the two masses. At this point, the combined gravitational attraction of the two bodies
produces a gravitational field that stabilizes the larger semi-major axis. L3 lies on the orbit of the
smaller mass, but 180 degrees away on the orbit on the opposite side of the larger mass. L4 and L5
are the most stable and exist on the orbit of the smaller mass but are located 60 degrees ahead of and
behind the smaller mass. LaGrange points are mathematically understood in a two-body system, but
are still present in an n-body system although less stable.

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mass in the solar system

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The great majority of the mass of the solar system is contained within the
Sun itself (99.86%), which has a dimension of hundreds of thousands of miles (864,000). Most of
the remaining mass is contained in the (8) major planets,

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our moon size

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Our Moon is the fifth largest
natural satellite in the solar system (2,160 mi.). Most of the moons of the planets are dozens to
hundreds of miles in diameter and there are over a hundred now known orbiting six of the planets.
Mercury and Venus have no natural satellites (known at this time)

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ceres

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On January 1, 1801 the first minor planet was discovered; Ceres (580 miles dia.)

Front 32

# of minor plaents

Back 32

Today, over 250,000 minor planets are known (some diameters down
to 40 meters), over 100,000 have been assigned numbers (indicating a stability or predictability of
the orbit), and over 14,000 have been named (indicating that a certain level of knowledge of
composition, perturbations, size, mass, etc. exists concerning the body). Six hundred and sixty seven
are considered dangerous Earth-crossing asteroids (Near Earth Objects; NEO)

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minor planets location

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Most, but not all, of the minor planets’ orbits lie between the orbit of Mars (1.5 A.U.) and Jupiter
(5.02 A.U.), in the asteroid belts. A popular astronomical myth states that a planet once orbited
there, but was torn apart by the tidal gravitational effects of Jupiter. This is not true. A planet may
have tried to form there, but never could get much past the planetisimal phase due to the
gravitational effects of Jupiter. If the masses of all the minor planets were brought together, it would
not even amount to the mass of our moon

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first asteroid discovered

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January 1st, 1801, Ceres was discovered by
Giuseppe Piazzi. It had a semi-major axis of 2.8 A.U. and it looked like the Titius-Bode Law might
be accurate. (The discoveries of Uranus and Neptune placed them nowhere near the locations
suggested by Titius-Bode and it was dismissed as a mathematical novelty.) At first this object was
called a planet. With a radius of only 470 km, Piazzi suggested the term planetoid, but eventually
lost out to Herschel's suggestion of asteroid.

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small solar system body

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Although Small Solar System Body is the preferred term by the IAU, the terms Asteroid, Minor
Planet, and Small Solar System Body are used interchangeably. The Small Solar System Bodies
between the orbits of Mars and Jupiter are usually referred to as the Asteroids, but despite the IAU's
actions in 2006 there is no clear-cut definition of a planet, minor planet, asteroid, or small solar
system body

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Elemets used in isolating hirayama groups

Back 36

Values or value ranges of semi-major axis (a), eccentricity (e), and inclination (i) are the most
common elements shared. The other two elements, the argument of the periapsis (w) and the
longitude of the ascending node (W) are subject to much (secular) perturbation with cyclical effects
and are not dominant in proper element analysis.

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asteroid families

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Families of asteroids, as being separate from groups, are recognized when chemical and material
makeup of the asteroids prove that the group originated from one parent body

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trojan asteroids

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The Trojans are two
groups of asteroids that orbit at Jupiter's L4 and L5 points. The Trojans at Jupiter's L4 are called the
Greeks and the Trojans at Jupiter's L5 are called the Trojans (not too confusing). There are also
recognized groups of Trojans associated with Neptune and Mars (very few members).

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Hildas asteroids

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They possess fairly eccentric orbits and an orbital
period (a) that has them fly in formation strictly defined by Jupiter's location. The Hildas experience
an orbital period with a 3:2 resonance with the orbital period of Jupiter. For every two trips around
the Sun for Jupiter, the Hildas orbit three times. This places the Hildas at the their aphelions when
Jupiter is 60 degrees ahead, 60 degrees behind, or 180 degrees away from the asteroid. The Hildas
are at their perihelions when Jupiter is 120 degrees ahead, 120 degrees behind, or 0 degrees
ahead/behind. The Hildas are doing the smart thing: staying away from Jupiter and they do a fairly
good job of it. There is a niche of orbital stability right at this semi-major axis/eccentricity pairing
that collects and keeps anything that wanders in.

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comets

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Comets are, for the most part, small objects, only a few miles across, with orbits of extreme
eccentricity that carry them far from the inner solar system for most of their orbital time period.
They only spend a very brief time near perihelion in the “inner” solar system. They spend the great
majority of their orbital periods traveling outward towards aphelion and passing through aphelion.
They then slowly fall toward perihelion, returning to the inner solar system for a repeat apparition.
A quick turn around the Sun and they’re off again. For an object with orbital parameters like the
Earth (low eccentricity, almost circular orbit), the difference between velocity at perihelion and the
velocity at aphelion is very small, only a percent or two. For objects with orbit eccentricities like
that of comets (in excess of .99…) the difference in velocities at the extremes of the orbit are
tremendous (ratios in excess of 100:1)

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composition of comets

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They are thought to be the ancient leftovers
from the formation of the solar system, and thus are made of material most similar to that which
formed the entire solar system some 4.6 billion years ago. They are known to contain a combination
of dust and ices that outgas and desorbs (their word, not mine) from the comet’s surface as it
approaches perihelion and is heated by the Sun. This material is ejected from the surface at a
relative velocity of only a few feet per second. It forms a cloud, the coma, around the body, nucleus,
of the comet, which is then illuminated by sunlight. This cloud, many thousands of miles across,
moves through the orbit with the cometary nucleus. As a result, when a comet approaches the Sun it
brightens significantly

Front 42

solar wind and comet tail

Back 42

As the comet approaches perihelion it also encounters a Solar Wind that is stronger closer to the Sun.
The Solar Wind is primarily made up of atomic and sub-atomic particles ejected from the Sun at
speeds approaching a million miles per hour. The pressure from this “wind” blows some of the
coma material away from the nucleus and away from the Sun forming a tail. The tail can trailmillions of miles behind the comet, not trailing behind the comet on its path, but trailing away
behind the comet pushed away from the Sun. As the comet passes through perihelion, the tail
swings around to be pushed out ahead of the comet by the Solar Wind. As the comet moves away
from the Sun, the tail actually precedes the comet being slightly accelerated by the Solar Wind
relative to the comet nucleus.

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comet tail

Back 43

Two different tails can be detected
photographically, each made up of the different materials being ejected from the comet. The dust
tail, highly reflective and easily seen, is pushed more slowly away from the comet and curves away
as the comet’s orbital path begins to bend around the Sun. The elusive ion tail is made of much
lighter (atomic) material and is pushed more directly away from the Sun, usually in a relatively
straight line. The ion tail is much dimmer than the dust tail and takes on a bluish tin

Front 44

dirty snowball

Back 44

The “dirty snowball”, or icy conglomerate model was put forward in 1950 by Fred Whipple. Also in
1950, kinematic studies of comet orbits by Jan Hendrik Oort predicted a distant reservoir of comets.
The icy conglomerate model also predicted that a comet would eventually boil away to nothing after
a finite number of trips through perihelion. An alternative outcome is for a comet to settle down
over time and become something closer to a small minor planet, having lost all of it’s outgas
material. Then, since comets have a finite lifetime and we still see comets today, there must be a
replenishing source of comets somewhere beyond the orbit of Neptune.

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meteoroid

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: A small piece of material in the solar system originating from minor planet “chipping”
or comet sublimation. These very small bodies follow the same laws of gravity, and will orbit the
Sun following Newton’s laws, just like larger bodies.

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meteor

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When a meteoroid enters the atmosphere at high speed it creates a glowing trail of ionized
gasses that can be visible from the surface of the Earth. This glowing trail is called a meteor and can
be visible from over two hundred miles away.

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apparation

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: An appearance or visit to the inner solar system by a comet on its orbit. Comets are
very small and nearly impossible to see except when they approach the Sun and pass through
perihelion. During this period comets will outgas material which is illuminated by the Sun.

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ioniazation

Back 48

The process of applying energy to an atom sufficient to “knock” an electron off of the
atom, creating an ion or charged atom.

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shooting stars

Back 49

are actually meteors

Front 50

hydorstatic equilibrium

Back 50

Hydrostatic equilibrium or hydrostatic balance occurs when compression due to gravity is balanced by a pressure gradient force in the opposite direction. For instance, the pressure gradient force prevents gravity from collapsing the Earth's atmosphere into a thin, dense shell, while gravity prevents the pressure gradient force from diffusing the atmosphere into space. Hydrostatic equilibrium is the current distinguishing criterion between dwarf planets and other small solar system bodies, and has other roles in astrophysics and planetary geology.

Front 51

hydrostatic equilibirum more

Back 51

The concept of hydrostatic equilibrium has also become important in determining whether an astronomical object is a planet, dwarf planet, or small solar system body. According to the definition of planet adopted by the International Astronomical Union in 2006, planets and dwarf planets are objects that have sufficient gravity to overcome their own rigidity and assume hydrostatic equilibrium. Sometimes this means a spheroid. However, in the cases of moons in synchronous orbit, near unidirectional tidal forces create a scalene ellipsoid, and the dwarf planet Haumea also appears to be ellipsoidal due to its rapid rotation.

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the radiant

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After midnight, the Earth turns into the debris cloud and the
meteoroids stream directly into the Earth and the meteor numbers rise dramatically. The meteors
appear to stream from a particular point in the sky defined by the intersection of the Earth’s orbital
path and debris column. This point typically rises around midnight (when the Earth begins to turn
into the stream) and is called the Radiant. Meteor showers typically get their names from the
constellation in which the Radiant is located.

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meteorite

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When a meteoroid, upon entering the atmosphere, has enough mass to survive the
encounter and land on the surface, then this piece of “space-rock” is referred to as a meteorite.
Meteorites come in a variety of designations segregated primarily by the chemical composition.

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asteroid belt

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A second source of meteoroids is the asteroid belt. Highly infrequent, but statistically predictable
collisions between the minor planets, produces debris of all sizes. The lighter material is slowly
affected by the solar wind streaming out from the Sun. The solar wind produces perturbations in the
orbits of the very fine material and causes them to lose energy and drift in towards the Sun. After
hundreds of millions of years this material may be crossing Earth’s orbit and may, by chance,
encounter the Earth. Meteoroids that originate in the Asteroid belt are typically more random in
their approach to Earth, encounter velocities are slower and particle sizes are more varied. Comet
origination meteoroids are typically smaller (finer) and encounter the Earth in a more organized
fashion. Any meteoroid robust and sizeable enough to survive the trip through the Earth's
atmosphere and land on the surface is called a meteorite.

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types of metoeroites

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Meteorites are classified by their chemical and mineral content. There are two main types of
meteorites; stony (chondrites) and metallic (irons), and a third, much rarer type which is a mixture of
stony and iron content. As a further classification, the stony (chondrite) meteorites are classified by
the size and number of chondrules within the meteorite. Meteorites that have been thoroughly
"cooked" by the Sun and its accretion disk, have no chondrules to speak of, and are called
achondrites (without chondrules). Meteorites that show chondrules are called chondrites, with subsub-classifications based on number, size and chemistry of the chondrules. The third subclassification of chondrites show larger chondrules with a measurable presence of volatile substances
in the mineral grains, primarily carbon and carbon compounds. These are known as carbonaceous
chondrites and they are among the oldest materials in the Solar System, having changed little since
their formation in the proto-stellar accretion disk 4.56 billion years ago.

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nickel and iron meteorites

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Nickel-Iron meteorites had to have originated inside of a body that was first, large enough to
differentiate and then cool. Through the collision and chipping process, pieces of the nickel-iron
core can then be isolated. If the core of the original body cooled and solidified very, very slowly,
large crystals will form in the iron. Typical crystals in metals smelted here on Earth have
microscopic crystal domains. Some Nickel-Iron meteorites will have huge crystal domains
measured in millimeters and centimeters. The surface of a slice of such a meteorite, polished and
etched with a mild acid will show these crystals. The patterns of the iron crystals are called
Widmanstatten Patterns and supply at least a partial history of the meteorite

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kupier

Back 57

Gerard Kuiper studied the orbits of short-period comets. These are
comets with orbital periods of less than 400 years and would then have semi-major axis values less
than 100 A.U.

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kupier belt

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Kuiper’s short-period comets showed more “moderate” orbital characteristics. They displayed
eccentricities in the .9 to .99 range and inclinations less than 20 or 30 degrees. These values are
unlike the planets and minor planets, but showed an origin from a disk-like structure around the Sun
beyond the orbit of Neptune.

The Kuiper Belt
is thought to start at about 40 A.U. from the Sun and continue out to about 1000 A.U. and contain 10
to 20 trillion objects in a relativly thin disk-like structure aligned with the plane of rest of the Solar
System.

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Jan Oort

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Jan Oort studied long-period comet orbits, orbits with periods greater than 400 years.
There are few comets with orbital periods just larger than 400 years, but many more with very long
orbital periods, thousands of years, tens of thousands of years, or longer.

The Oort cloud begins at about 1000 A.U. from the Sun, continues out to an estimated
50,000 or 100,000 A.U., and contains several billion objects. Keep in mind that these regions are
just the origin of comets and perturbations will reduce the orbital parameters to more “normal”
comet values over time.

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Oort Cloud

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Oort’s long-period comets had even more radical orbital
characteristics. Eccentricities in excess of .999 and inclinations of all values that show no pattern at
all, indicating an origin much farther out and three dimensional in nature

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pluto

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Pluto should be considered among these Trans-Neptunian Objects (TNOs), or Kuiper-Belt-Objects
(KBOs), or sometimes called Edgeworth-Kuiper-Belt-Objects (EKBOs), because of its semi-major
axis value. Pluto had just been the largest of these objects, large enough to be discovered by Clyde
Tombaugh during his survey of the outer Solar System in 1930. Pluto shares an interesting
relationship with Neptune in the sense that Pluto’s orbital period is 1 1/2 times that of Neptune. This
establishes a 3:2 resonance in the orbital periods such that Neptune and Pluto come “together” every
three trips around the Sun for Neptune and every two orbits for Pluto. This reinforces the orbital
period and keeps it stable over long periods.

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Plutnios

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About 1/3 of all the Kuiper Belt Objects known share this same 3:2 resonance with Neptune. This
produces the same stabilizing effect as the resonance with Pluto and acts as a collector of KBOs into
this resonance. This is the same kind of mechanism that produces the groupings of the minor
planets. These resonant KBOs are usually referred to as the Plutinos, with Pluto being the largest
(1400 mi.). One of the other large Plutinos is Quaour (2002LM60; 800 mi.) another recent, large
KBO discovery.

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oort cloud more

Back 63

The Oort Cloud, the presumed source of long period comets, is completely
unobservable from Earth at this point in time. The Oort Cloud probably contains small planetisimal
sized objects rather than a mixture of object sizes like the Kuiper Belt. Observing an object dozens
of miles across from a distance of many thousands of A.U. is well beyond our current technologies.
(An Oort Cloud object occulting a star?)
The Oort Cloud is now thought to be populated by objects that originally existed within the orbit of
Neptune and thus are partially thermally processed objects. Encounters of planetisimals with Jupiter
and Saturn are usually fatal in the sense that the planetisimals merge with the growing planets

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Pegasai 51

Back 64

In 1995 a dramatic announcement was made about a relatively nondescript star; 51 Pegasi. 51
Pegasi (in the constellation of Pegasus) is a star very similar to our Sun and is about 50 light years
away from the Earth, just barely visible to the naked eye in a dark-sky environment (magnitude 5.5).
It seems that a planet had been discovered orbiting that star!

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Quasi-Satellite

Back 65

an object in a 1:1 orbital resonance with its planet that stays close to the planet over many orbital periods.

They orbit the Sun

Earth has 4 of these and Venus has 1

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Opposition

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Planets and minor planets come into a syzygy with the Earth and the Sun
every so often and this alignment presents the best opportunity for observation (or discovery) for the
object.

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Plutino

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a trans-Neptunian object in 2:3 mean motion resonance with Neptune.

For every 2 orbits that a plutino makes, Neptune orbits 3 times.

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Pluto

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Discovered by Clyde W. Tombaugh

Discovery date February 18, 1930

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Quaoar

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a binary trans-Neptunian object and dwarf planet candidate orbiting the Sun in the Kuiper belt.

It was discovered on June 4, 2002 by astronomers Chad Trujillo and Michael Brown

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Eris

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s the most massive known dwarf planet[i] in the Solar System and the ninth most massive body known to orbit the Sun directly.

Eris was first identified in January 2005 by a Palomar Observatory-based team led by Mike Brown

I THINK also known as 2003UB313