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 Neptune year).

Neptune 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.

The hot inner core is surrounded by amantle consisting of water, ammonia and methane.

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 Moons

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.

The 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 larger bodies.

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.

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