Neptune / Introduction
It is cold and windy on Neptune, the eighth planet of our Solar System. Its
existence and position was accurately calculated before the planet was ever
seen. Astronomers had observed slight perturbations in the orbit of the
planet Uranus. In the mid-19th century, the British astronomer Adams and his
French colleague Leverrier independently calculated the existence and
position of a celestial object that caused these perturbations. It was only
a few months later that Neptune was actually seen for the first time.
It was in 1846 when the German astronomer Galle succeeded indetecting the
object at the previously calculated position.More detailed knowledge of
Neptune was not gathered until 1989, when the Voyager 2 spacecraft flew
close to Neptune.
The diameter of Neptune at its equator is almost 50,000 kilometers. Its mean
distance from the sun is 4.5 billion kilometers and it takes Neptune nearly
165 years to complete a full orbit around the sun. The atmosphere of the
planet shows much more distinct features than that of its neighbor Uranus.
There is for example a large dark spot that indicates a storm system several
times the size of the earth. Winds here blow at speeds in excess of 2000
kilometers per hour. As the atmosphere of Neptune is very dense, this speed
is almost equal to the velocity of sound waves on the planet.
Neptune is the most stormy planet in the Solar System and emits 2.5 times
the amount of energy that it receives from the sun.
It is also the fourth planet with a ring system and has eight moons. One of
them called Triton is the coldest place in our Solar System.
Orbit of Neptune
The mean distance between the sun and Neptune is 4.5 billion kilometers and
equals approximately thirty astronomical units (AU). One astronomical unit
is the distance between the earth and the sun. It takes Neptune
approximately 165.5 years to complete one full orbit around the sun (= 1
rotates once on its own axis every 16 hours and 7 minutes. However, it is
impossible to establish this rotation cycle by means of observation as the
structure of the planetís atmosphere does not provide us with any fixed
point to follow.
The length of a day on Neptune was established by means of radio
astronomy.The planet features a distinct radiation, which appears to
originate from a magnetic field in
the interior of the planet. Similar radiation has also been observed on the
other giant gas planets. Neptune shows a moderate inclination of its
rotation axis towards the plane of its orbit. The angle of inclination is
29.5 degrees and is therefore only slightly larger than that of the earth,
Mars and Saturn.
Composition of Neptune
Neptune shows a composition and structure very similar to that of Uranus. As
Neptune is slightly smaller than Uranus and has a greater density of matter,
its hot inner core is believed to be larger in size than that of its
neighbor. When the density of water is defined as 1, Uranus has a density of
matter of 1.3 and Neptune of 1.65.
hot inner core is surrounded by amantle consisting of water, ammonia and
There is no clearly defined border between that layer and the planetís
atmosphere, which consists mainly of hydrogen (85%) and helium (13%).There
are also small quantities of methane that are responsible for the strikingly
blue appearance of the planet.
The atmosphere of Neptune features a few more distinct structures than are
found in the atmosphere of Uranus .
There is first of all a large dark
spot located to the south of the
equator. In relation to the planetís
size, it is of a similar dimension as
the Great Red Spot on Jupiter.
The dark spot is in fact a storm system.
The cyclone on Neptune is even more powerful than the one on Jupiter. It
reaches speeds of up to 2200 kilometers per hour.There is no more turbulent
place to be found in the Solar System.
White clouds of methane ice can be observed in the upper layers of the
atmosphere. These clouds produce shadows on the planetís atmosphere and are
therefore believed to be very distant from the planet. Near the south pole,
there is a smaller cyclone, visible as a small dark dot called scooter.
These two turbulent zones revolve around the planet in opposite directions.
The atmosphere is surrounded by a hazy layer containing carbon and hydrogen.
Neptune has eight satellites, four of them located inside the ring system
and four of them outside. Two of the inner moons, Naiad and Thalassa, are
shepherd moons. Their neighbors are Despoina and Galatea.
next moon outside the rings is Larissa, followed by Proteus, which has
already a distance from the planet of 118,000 kilometers.
Its diameter is 400 kilometers and its surface is covered in craters.
Triton is the largest of the Neptunemoons with a distance of approximately
355,000 kilometers from Neptune.
It orbits the planet in the opposite directions to the other smaller
satellites. Its diameter of 2760 kilometers far exceeds the dimensions of
its smaller neighbors.
The most striking feature of
Triton is its extremely low
temperature. It reaches minus
235 įC, which is very close to
the absolute zero of minus
273 įC (0 Kelvin). The temperatureon Triton is the lowest measured anywhere
in the Solar System.
Tritonís noth pole has a distinct blue tint, while its south pole appears in
pink. There are ice volcanoes in its southern hemisphere expelling nitrogen
vapour and dust.
Nereid has the largest orbit of the Neptune moons. The satellite is 5.5
million kilometers distant from Neptune. Nereid is rather small with a
diameter of approximately 250 kilometers but was nevertheless one of the
first known moons of the planet.The other satellites were only discovered by
the Voyager 2 spacecraft. Astronomers assume that there are more shepherd
moons to be found inside the rings of the planet. All the small moons of
Neptune consist of ice and rock.
There are two narrow and two broad rings around Neptune. The rings are not
particularly prominent and contain mainly ice particles. The outermost of
the narrow rings features some areas of greater density believed to contain
This dense areas are of special interest for scientists as it is assumed
that matter is normally equally dispersed in these rings. The total quantity
of matter located in the rings of Neptune would just about be enough to form
a small moon.