| Neptune Essay, Research Paper
Little was known about Neptune ,which was discovered in 1846, until
the Voyager 2 encounter in 1989. It has a similar composition to Uranus and
is close in mass to Uranus. Its thick atmosphere made of hydrogen, helium,
and some methane and ammonia, gives it a bluish color.
DISCOVERY
On August 25, 1989, the voyager discovered Neptune, but only after
traveling 12 years at an average velocity of 19 kilometers a second (about 42
miles an hour). The Voyager 2 observed Neptune almost continuously from
June to October 1989. This discovery though, gives us just about all the info
about Neptune.
BACKGROUND
Astronomers have studied Neptune since September 23, 1846, when
Johann Gottfried Galle, of the Berlin Observatory, and Louis d’Arrest, an
astronomy student, discovered the eighth planet on the basis of mathmatical
predictions by Urbain Jean Joseph Le Verrier. Scarcely after Galle and
d’Arrest first saw Neptune, British astonomer William Lassell spotted a moon
orbiting the planet and named it Triton (Which is explained in greater detail
later in the report).
In 1949 astonomer Gerard Kuiper discovered Nereid, the second
largest moon of Neptune. Nereid is only about 340 kilometers (210 miles) in
diameter and is so far from Neptune that it requires 360 days to make one
orbit.
In 1981, a star would pass behind Neptune so that observers could
measure the starlight and how it changed as it passed through the upper layer
of Neptune’s atmosphere. But the star’s light flashed on and off before
Neptune passed in front of it. Astronomers concluded that some material
orbits Neptune, and was responsible for occasional blockage of the star’s
light.
NEPTUNE FACTS AND FIGURES
Neptune is the eighth planet from the sun and the fourth largest by
diameter. Neptune is smaller in diameter but larger in mass than Uranus.
orbit: 4,504,000,000 km (or 30.06 Astronomical Units) from the sun.
diameter: 49,528 km through the equator
mass: 1.0247e26 kg
In Roman Mythology Neptune (Greek: Poseidon) was the god of the sea.
Because Pluto’s orbit is so eccentric, it sometimes crosses the orbit of
Neptune. Since 1979 Neptue has been the most distant planet from the sun
but Pluto will be the most distant in 1999.
Neptune’s blue color is a result of the absorption of red light by
methane in the atmosphere.
Neptune’s winds are the fastest in the solar system, reaching 2000
km/hour. Most of the winds blow in a westward direction, which is opposite
to the rotation of the planet. Near the Great Dark Spot, there are opposite,
or retrograde winds blowing up to 1500 miles an hour–the strongest winds
measured on any planet.
Neptune has an internal heat source–it radiates more than twice as
much energy as it receives from the sun.
At the time of the Voyager encounter, Neptune’s most prominent
feature was the Great Dark Spot in the southern hemisphere. Neptune’s
winds blew the Great Dark Spot westward at 300 meters/second (700mph).
Voyager 2 also say a small irregular white cloud that zips around Neptune
every 26 hours or so known as “The Scooter”. However, observations show
that the Great Dark Spot has disappeared. A few months later, a new dark
spot in Neptune’s northern hemisphere was discovered. This indicates
thats Neptune’s atmosphere changes rapidly, perhaps due to slight changes in
the temperature differences between the tops and bottoms of the clouds.
Another storm, Dark Spot 2, is smaller than the Great Dark Spot and is oval
in shape. It has a white cloud hovering above its center.
The atmosphere of Neptune is hotter near the equator, cooler in the
mid latitudes and warm again at the south pole. Temps in the stratosphere
were measured to be 750 kelvins, while at the 100 millibar pressure level,
they were measured to be 55 K (-360 degrees F).
RINGS
Neptune, like Saturn, has rings. The rings are very dark but their
composition is unknown. Neptune’s rings have been given names: the
outermost Adams (which contains three prominent arcs now named Liberty,
Equality, and Fraternity), next is an unnamed ring (whose outer extensions
are called Lassell and Arago), and finally the faint but broad Galle. Detecting
these rings as full rings was not easy because of the fact that the material was
so fine and diffuse. Scientists were able to sort out the rings:
The “main ring” (a.k.a. 1989N1R) orbits Neptune about 38,100
kilometers above the cloud tops. The main ring contains three seperate
regions where the material is brighter and denser, and explains most of the
sightings or “ring arcs”.
The “Inner Ring” (1989N2R) is about 28,400 km (17,700 miles) above the cloud tops.
The “Inside Diffuse Ring” (1989N3R) is a complete ring located about 17,100 kilometers from Neptune’s cloud tops. Some scientists suspect that this ring may extend all the way down to Neptune’s cloud tops.
An area called “the Plateau,” a broad, diffuse sheet of fine material just outside the so called “inner ring”.
The material varies a lot in size from ring to ring. The largest proportion of fine material is about the size of smoke particles, is in the Plateau. All other rings contain a greater portion larger material.
SMALL SATELITES
In addition to the previously known moons Triton and Nereid,
Voyager 2 found six more moons orbiting Neptune, for a total of eight
known moons.
1989N1, like all six of Neptune’s newly discovered small moons, is one
of the darkest objects in the solar system. It circles Neptune at a
distance of about 92,800 km above the cloud tops. Its about 400 km in
diameter.
1989N2, is only about 48,800 km from Neptune, and circles the planet
in about 13 hours 18 minutes. Its diameter is about 190 km.
1989N3, only 27, only about 27,700 km from Neptune’s cloud, orbits every 8 hours. Its diameter is about 150 km.
1989N4 lies 37,200 km from Neptune. 1989N4, diameter 180 kilometers, completes an orbit in 10 hours, 18 minutes.
1989N5 appears to be about 80 kilometers in diameter. It orbits Neptune in 7 hours, 30 minutes about 15,700 miles above the cloud tops.
1989N6, the last satelite discoverd, is about 54 kilometers in diameter and orbits Neptune about 23,200 km above the clouds in 7 hours, 6 minutes.
TRITON
Neptune’s largest moon, Triton, exists, 30 AU from the sun.
Temperature on this frigid body is so low that molecules which are present in
a gaseous form on the other planets condense to form ice coating over the
landscape. The ice coatings are made of mostly nitrogen, with methane,
carbon monoxide, and carbon dioxide each making up to about 1% of the ice.
The rocky core of Triton is covered by a huge layer of water ice that
preserves the craters, faults, and volcanic landforms.
Over Triton’s 165 year seasonal cycle,a layer of volatile ice about a
meter deep will move across the face of the planet over distances of 1,000
km or more. If we return to the surface of Triton in a few decades it will
probably not be like the images that the Voyager got in 1989. As the ices
move around the moon the amount of sunlight falling on them will change
and so will their temperature. The surface pressure on Triton could change
by a factor of 10 or 100 during the course of a season.
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