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The Planets .... brought to you by QuasArt Web Designs.
T H E S O L A R S Y S T E M
CHAPTERS
I II III IV V VI VII
INTRODUCTION
I
Solar System, the sun and the celestial bodies orbiting the sun,
including the nine planets and their satellites; the asteroids,
comets, and meteoroids; and interplanetary dust and gas.
The term may also refer to a group of celestial bodies orbiting
another star. In this article, solar system refers to the system
that includes the earth and the sun.
Find
the exact location of any Body in the Solar System Astromoners Referance
:
Solar
System Active JAVA APPLET (this little net gadget is pretty amazing
a must see).
The dimensions of this system are specified
in terms of the mean distance from the earth to the sun, called the
astronomical unit (AU). One AU is 150 million km (about 93 million
mi). The most distant known planet, Pluto, has an orbit at 39.44 AU
from the sun. The boundary between the solar system and interstellar
space-called the heliopause-is estimated to occur near 100 AU. The
comets, however, achieve the greatest distance from the sun; they
have highly eccentric orbits (see Orbit) ranging out to 50,000 AU
or more. This solar system was the only planetary system known to
exist until 1995, when astronomers discovered a planet about 0.6 times
the mass of Jupiter orbiting the star 51 Pegasi. Soon after, astronomers
found a planet about 8.1 times the mass of Jupiter orbiting the star
70 Virginis, and a planet about 3.5 times the mass of Jupiter orbiting
the star 47 Ursae Majoris. Since then, astronomers have found planets
and disks of dust in the process of forming planets around many other
stars. Many astronomers think it likely that solar systems of some
sort are numerous throughout the universe.
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THE
SUN AND THE SOLAR WIND
II
The sun is a typical star of intermediate size and luminosity. Sunlight
and other radiation are produced by the conversion of hydrogen into
helium in the sun's hot, dense interior (see Nuclear Energy). Although
this nuclear fusion is destroying 600 million metric tons of hydrogen
each second, the sun is so massive (2 × 1030 kg, or 4.4 × 10 30 lb)
that it can continue to shine at its present brightness for 6 billion
years. This stability has allowed life to develop and survive on earth.
For all the sun's steadiness, it is an extremely active star. On its
surface dark sunspots bounded by intense magnetic fields come and
go in 11-year cycles; sudden bursts of charged particles from solar
flares can cause auroras and disturb radio signals on earth; and a
continuous stream of protons, electrons, and ions leaves the sun and
moves out through the solar system, spiraling with the sun's rotation.
This solar wind shapes the ion tails of comets and leaves its traces
in the lunar soil, samples of which were brought back from the moon's
surface by piloted U.S. Apollo spacecraft.
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ITHE
MAJOR PLANETS
III
Nine major planets are currently known.
They are commonly divided into two groups:
| The
Inner Planets (Mercury, Venus, Earth, and Mars) The Outer Planets (Jupiter, Saturn, Uranus, Neptune, and Pluto). |
The Inner Planets are small and are composed primarily of rock
and iron.
THE INNER PLANETS
Mercury is surprisingly dense, apparently
because it has an unusually large iron core. With only a transient
atmosphere, Mercury has a surface that still bears the record of bombardment
by asteroidal bodies early in its history.
Venus has a carbon dioxide atmosphere 90
times thicker than that of Earth, causing an efficient greenhouse
effect by which the Venusian atmosphere is heated. The resulting surface
temperature is the hottest of any planet-about 477° C (about 890°
F).
Earth is the only planet with abundant liquid
water and life. Strong evidence exists that
Mars once had water on its surface, but now
its carbon dioxide atmosphere is so thin that the planet is dry and
cold, with polar caps of solid carbon dioxide, or dry ice.
The Outer Planets (except Pluto) are much larger and
consist mainly of hydrogen, helium, and ice.
THE OUTER PLANETS
Jupiter is the largest of the planets.
Its hydrogen and helium atmosphere contains pastel-colored clouds,
and its immense magnetosphere, rings, and satellites make it a planetary
system unto itself.
Saturn rivals Jupiter, with a much more
intricate ring structure and more satellites, including one with an
atmosphere-Titan.
Uranus and Neptune are deficient in hydrogen
compared with Jupiter and Saturn; Uranus,
also ringed, has the distinction of rotating at 98° to the plane of
its orbit.
Pluto seems similar to the larger, icy satellites
of Jupiter or Saturn. Pluto is so distant from the sun and so cold
that methane freezes on its surface.
Very little is known about Pluto because
of it's great distance from the Sun.
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IOTHER
ORBITING BODIES
THE ASTERIOD BELT
IV
Asteriod
IDA 243
Asteroids are extremely small planets that orbit the sun and are situated
primarily between the orbits of Mars and Jupiter. The Galileo
spacecraft, a space probe launched by the United States National Aeronautics
and Space Administration (NASA), photographed the asteroid 243 Ida
in August 1993. The space probe detected a moon orbiting Ida, making
Ida the only asteroid known to have a satellite.
(shown below) Jet Propulsion Laboratory/Gamma Liaison
The asteroids are small rocky bodies that move in orbits primarily
between the orbits of Mars and Jupiter. Numbering in the thousands,
asteroids range in size from Ceres, which has a diameter of 1000 km
(620 mi), to microscopic grains. Some asteroids are perturbed, or
pulled by forces other than their attraction to the sun, into eccentric
orbits that can bring them closer to the sun. If the orbits of such
bodies intersect that of the earth, they are called meteoroids. When
they appear in the night sky as streaks of light, they are known as
meteors, and recovered fragments are termed meteorites. Laboratory
studies of meteorites have revealed much information about primitive
conditions in our solar system. The surfaces of Mercury, Mars, and
several satellites of the planets (including Earth's moon) show the
effects of an intense bombardment by asteroidal objects early in the
history of the solar system. On Earth that record has eroded away,
except for a few recently found impact craters. Some meteors and interplanetary
dust may also come from comets, which are basically aggregates of
dust and frozen gases about 5 to 10 km (about 3 to 6 mi) in diameter.
Comets orbit the sun at distances so great that they can be perturbed
by stars into orbits that bring them into the inner solar system.
As comets approach the sun, they release their dust and gases to form
a spectacular coma and tail. Under the influence of Jupiter's strong
gravitational field, comets can sometimes adopt much smaller orbits.
The most famous of these is Halley's Comet, which returns to the inner
solar system at 75-year periods. Its most recent return was in 1986.
In July 1994 fragments of Comet Shoemaker-Levy 9 bombarded Jupiter's
dense atmosphere at speeds of about 210,000 km/h (130,000 mph). Upon
impact, the tremendous kinetic energy of the fragments was converted
into heat through massive explosions, some resulting in fireballs
larger than Earth. Comets circle the sun in two main groups. The Kuiper
belt is a ring of debris that orbits the sun beyond the planet Neptune.
Many of the comets with periods of less than 500 years are members
of the Kuiper belt. The Oort cloud is a theoretical, spherical cloud
of comets extending to the edge of the solar system. Astronomers believe
that comets with very long periods reside in the Oort cloud. A chunk
of dust and ice may stay in the Oort cloud for thousands of years.
Nearby stars sometimes pass close enough to the solar system to push
an object in the Oort cloud into an orbit that takes it close to the
sun. Many of the objects that do not fall into the asteroid belts,
the Kuiper belt, or the Oort cloud may be comets that will never make
it back to the sun. The surfaces of the icy satellites of the outer
planets are scarred by impacts from such bodies. The asteroid-like
object Chiron, with an orbit between Saturn and Uranus, may itself
be an extremely large inactive comet. Similarly, some of the asteroids
that cross the path of Earth's orbit may be the rocky remains of burned-out
comets. Chiron and similar objects called the Centaurs probably escaped
from the Kuiper belt and were drawn into their irregular orbits by
the gravitational pull of the giant outer planets, Jupiter, Saturn,
Neptune and Uranus. The sun was also found to be encircled by three
rings of interplanetary dust. One of them, between Jupiter and Mars,
has long been known as the cause of zodiacal light, a faint glow that
appears in the east before dawn and in the west after dusk. The other
two rings, one lying only two solar widths away from the sun, the
other occurring in the region of the asteroids, were discovered in
1983.
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Asteriod GASPERA
951
This animation shows the shape and surface of Gaspra. It is based
upon Phil Stooke's shape model and shaded relief drawing of Gaspra.
Video Gaspera in Rotation
231 KB MPEG
This animation shows the shape of asteroid 951 Gaspra. It is
based upon Phil Stooke's shape model.
Gaspra Shape Model 61
KB MPEG
Gaspra (Asteroid 951- above) was discovered by Grigoriy N. Neujamin
in 1916. Neujamin named Gaspra after a Black Sea retreat that was
visited by contemporaries such as Tolstoy and Gorky. Gaspra was just
another small asteroid that was given very little attention until
it was discovered that the trajectory of the Galileo spacecraft would
take it close to Gaspra. Following this discovery, observers through
out the world made Gaspra a prime target of study. Gaspra was found
to have an elongated shape with a rotational period of 7.04 hours.
On October 29, 1991, Galileo came within 1,600 kilometers (1,000 miles)
of Gaspra. They passed each other at 8 kilometers (5 miles) per second.
This was the first time that a spacecraft made a fly-by of an asteroid.
Gaspra is an irregular body with dimensions of about 20 x 12 x 11
km (12.5 x 7.5 x 7 miles). Its surface reflects approximately 20 percent
of the sunlight striking it. Gaspra is classified as an S-type asteroid
and is likely composed of metal-rich silicates and perhaps blocks
of pure metal. It is a member of the Flora family. Several craters
are visible on Gaspra, but none approach the scale of the asteroid's
radius. The fact that Gaspra is irregular in shape and lacks any large
craters suggests that it has a comparatively recent origin, most likely
from the collisional breakup of a larger body. Gaspra has probably
been in its present state for the last 300 to 500 million years.
| Asteroid Summary |
|---|
| Num | Name | Radius (km) | Distance* (10^6km) | Albedo | Discoverer | Date |
|---|---|---|---|---|---|---|
| 1 | Ceres | 457 | 413.9 | 0.10 | G. Piazzi | 1801 |
| 511 | Davida | 168 | 475.4 | 0.05 | R. Dugan | 1903 |
| 15 | Eunomia | 136 | 395.5 | 0.19 | De Gasparis | 1851 |
| 52 | Europa | 156 | 463.3 | 0.06 | Goldschmidt | 1858 |
| 951 | Gaspra | 17x10 | 205.0 | 0.20 | Neujmin | 1916 |
| 10 | Hygiea | 215 | 470.3 | 0.08 | De Gasparis | 1849 |
| 243 | Ida | 58x23 | 270.0 | ? | J. Palisa | 29 Sep 1884 |
| 704 | Interamnia | 167 | 458.1 | 0.06 | V. Cerulli | 1910 |
| 2 | Pallas | 261 | 414.5 | 0.14 | H. Olbers | 1802 |
| 16 | Psyche | 132 | 437.1 | 0.10 | De Gasparis | 1852 |
| 87 | Sylvia | 136 | 521.5 | 0.04 | N. Pogson | 1866 |
| 4 | Vesta | 262.5 | 353.4 | 0.38 | H. Olbers | 1807 |
* Mean distance from the Sun
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IMOVEMENTS
OF THE PLANETS AND THEIR SATELLITES
V
If one could look down on the solar system from far above the North
Pole of the earth, the planets would appear to move around the sun
in a counterclockwise direction. All of the planets except Venus and
Uranus rotate on their axes in this same direction. The entire system
is remarkably flat-only Mercury and Pluto have obviously inclined
orbits. Pluto's orbit is so elliptical that it is sometimes closer
than Neptune to the sun. The satellite systems mimic the behavior
of their parent planets and move in a counterclockwise direction,
but many exceptions are found. Jupiter, Saturn, and Neptune each have
at least one satellite that moves around the planet in a retrograde
orbit (clockwise instead of counterclockwise), and several satellite
orbits are highly elliptical. Jupiter, moreover, has trapped two clusters
of asteroids (the so-called Trojan asteroids) leading and following
the planet by 60° in its orbit around the sun. (Some satellites of
Saturn have done the same with smaller bodies.) The comets exhibit
a roughly spherical distribution of orbits around the sun. Within
this maze of motions, some remarkable patterns exist: Mercury rotates
on its axis three times for every two revolutions about the sun; no
asteroids exist with periods (intervals of time needed to complete
one revolution) 1/2, 1/3, ..., 1/n (where n is an integer) the period
of Jupiter; the three inner Galilean satellites of Jupiter have periods
in the ratio 4:2:1. These and other examples demonstrate the subtle
balance of forces that is established in a gravitational system composed
of many bodies. VITHEORIES OF ORIGIN Despite their differences, the
members of the solar system probably form a common family. They seem
to have originated at the same time; few indications exist of bodies
joining the solar system, captured later from other stars or interstellar
space. Early attempts to explain the origin of this system include
the nebular hypothesis of the German philosopher Immanuel Kant and
the French astronomer and mathematician Pierre Simon de Laplace, according
to which a cloud of gas broke into rings that condensed to form planets.
Doubts about the stability of such rings led some scientists to consider
various catastrophic hypotheses, such as a close encounter of the
sun with another star. Such encounters are extremely rare, and the
hot, tidally disrupted gases would dissipate rather than condense
to form planets. Current theories connect the formation of the solar
system with the formation of the sun itself, about 4.7 billion years
ago.
The fragmentation and gravitational collapse of an interstellar cloud
of gas and dust, triggered perhaps by nearby supernova explosions,
may have led to the formation of a primordial solar nebula (see Nova
and Supernova). The sun would then form in the densest, central region.
It is so hot close to the sun that even silicates, which are relatively
dense, have difficulty forming there. This phenomenon may account
for the presence near the sun of a planet such as Mercury, having
a relatively small silicate crust and a larger than usual, dense iron
core. (It is easier for iron dust and vapor to coalesce near the central
region of a solar nebula than it is for lighter silicates to do so.)
At larger distances from the center of the solar nebula, gases condense
into solids such as are found today from Jupiter outward. Evidence
of a possible preformation supernova explosion appears as traces of
anomalous isotopes in tiny inclusions in some meteorites. This association
of planet formation with star formation suggests that billions of
other stars in our galaxy may also have planets. The high frequency
of binary and multiple stars, as well as the large satellite systems
around Jupiter and Saturn, attest to the tendency of collapsing gas
clouds to fragment into multibody systems.
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WEB
LINKS
VII
Virtual
Solar System
National Geographic Society's
Awesome 3D Model of the Solar System
Requires Plug-In download
The Planetary Society
Non Profit Organization
The Apollo Program
NASA
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Planets | Sun | Mercury | Venus | Earth | Mars | Jupiter | Saturn | Uranus | Neptune | Pluto