Science An Overview of Neptune

Discovery of Neptune

First Discovery

Telescope

Galileo

Additional Sightings

Second and Official Discovery

Mathematics

Adams, Le Verrier, & Galle

The Planet

Atmospheric Conditions

Characteristics

Neptune's Orbit

Comparison to Earth

Neptune is the eighth, and furthest, planet from the sun. This blue gas giant has been named in the tradition of other planets, with a name taken from mythology; Neptune is the Roman god of the sea. The planet has an interesting history, and characteristics which clearly differentiate it from other planetary bodies. The aim of this paper is to examine the planet, looking at its discovery as well as its' characteristics and the way it compares to earth.

2.

Discovery of Neptune

The official discovery of Neptune occurred in 1846, but the history of discovery can be traced back much further, with the apparent identification of the planet more than two centuries before it official recognition. Hindsight indicates that the planet had been recorded by a number of observers beginning more than two centuries before.

2.1

First Discovery

2.1.1

Telescope

The first discovery only occurred after the development of Tesco's. Although five planets of the solar system may be observed easily with the naked eye, and Uranus has the potential to be seen unaided is observed from a perfectly dark place, Neptune does not have sufficient brightness to be observed without a telescope. This with a brightness magnitude between +7.7, and +8, the planet will never be visible to be seen unaided (Williams, 2014; Grosser, 1962). Not only does the planet have low magnitude brightness, the planets own moons are able to outshine it (Williams, 2014). Therefore, the initial observation of Neptune occurs only after the telescope comes into use.

2.1.2

Galileo

The first observations of Neptune appear to have taken place in 1613, when Galileo Galilei recorded the observation of an object in a drawing on 28 December (Grosser, 1962). Galileo made a similar observation on 27 January 1613, recording an object that appeared to be very close to Jupiter (Grosser, 1962). Traditionally, it is believed that Galileo believed that the planet, which would later be named Neptune, was a fixed star as it appeared to be stationary in the sky, rather than moving in orbit as would be expected of a planet (Jones, 2014). However, at the point of discovery Neptune just entered the retrograde this stage of its cycle on the day it was initially observed explaining its apparent lack of movement (Jones, 2014). However, in more recent research undertaken by David Jamieson, an Australian physicist, it appears that Galileo may have been aware that is observation was significant, as the notation for 28 January 1613 is made in a different ink, indicating the been differentiated, and further observations, including a sketch on 6 January appears to indicate he was observing this heavenly body in a systematic manner (Jones, 2014). However, without any specific nose, and no evidence of further observational attempts, the evidence is inconclusive regarding his interpretation of the observation (Jones, 2014).

2.1.3

Additional Sightings

Galileo was not the only individual studying the heavens, who noted the presence of an object that would later become known as Neptune. In all cases, the telescopes were of limited strength, so the relatively dull planet would only have appeared as a small and difficult to observe. However, it is also recorded that it was observed in 1795 by Jerome Lalande who observed it from the Paris Observatory, and then in 1830 by John Herschel, although neither recognized the body as a planet, both of whom classified it as a star.

2.2

Second and Official Discovery

The story of the official discovery of Neptune varies from other planets which had been discovered up to that point, instead of being observed and then studied; the presence of a planet was identified using mathematical calculations to indirect evidence, rather than its presence being observed from a telescope.

2.2.1

Mathematics

The mathematical discovery that Neptune should exist starts with the publication of astronomical tables by Alexis Bouvard. These tables, published in 1821, recorded the orbit of Uranus, and provided a basis for a theoretical orbit with that observed. The observations indicated significant deviations from the expected path, which resulted in a hypothesis by Bouvard that there were other gravitational influences impacting on the planets orbit (Jones, 2014).

2.2.2

Adams, Le Verrier, & Galle

In 1843 John Couch Adams examined the data regarding Uranus's orbit. Adams collected...

Independently in France, the astronomer Urbain Le Verrier was also working on a similar project, observing differences between the movements of Uranus, and the theoretical path according to tables, but his work is undertaken without support from his peers (Jones, 2014). On reviewing the findings of Adams and Le Verrier, and finding a significant alignment between the independent works of these two theorists, Sir George Airy approached Challis, asking him to look for the planet, but despite searching between August and September of 1846, it was not found (Jones, 2014; Grosser, 1962). At the same time, Le Verrier had written to Johann Galle at the Berlin Observatory, asking him to observe the sky, in the region he predicted in order to determine if the displacement characteristics with those of the planet. On 23 September 1846, the same day that the letter was received by Galle, the planet was observed approximately 1° from the prediction made by Le Verrier, and approximately 12° from the placement that Adams had predicted (Airy, 1846). Subsequent to this revelation, is Challis realized that he had observed the planet twice on 8 August and 12 August, but less ridiculous approach to his work has meant it failed to recognize it. Controversy in disagreement existed regarding the attribution of the discovery, which was eventually given to both Adams and Le Verrier.
3.

The Planet

3.1

Atmospheric Conditions

Neptune is a gas giant, and similar to other gas giants, is composition has two regions without a firm surface (Kerrod, 2000) the 'surface' is defined at the point where the pressure on the planet is equal to the pressure on us at sea level. (Kerrod, 2000) The atmospheric composition by volume is made up of 80% molecular hydrogen with a 3.2% uncertainty, and 19% helium with a 3.2% uncertainty, and 1.5% methane, Ms 0.5% uncertainty (Williams, 2014). There are also trace elements of hydrogen deuteride, methane, with aerosols of ammonia ice, water ice, ammonia hydrosulfide, and the potential for methane ice (Williams, 2014). The temperature at the surface is approximately 55K, or -201 C, and as the altitude increases the temperature decreases (Williams, 2014). The higher surface temperature reflects the way more heat is created by the planets rotation than is gained from the rays of the sun, however, when reaching the upper stratosphere the temperature starts to increase again (Fletcher et al., 2010).

Neptune has clouds which vary with altitude. At the highest levels there are frozen methane cirrus clouds, which have been observed casting shadows on clouds at an altitude 35 miles lower (Fletcher et al., 2010). Underneath these methane clouds it is believed there are clouds made up of ammonium sulfide and hydrogen sulfide and water (Fletcher et al., 2010).

The planet has powerful storms, with winds of up to 1,305 miles per hours, giving nature some of the most extreme weather in the solar system, with winds that are none times faster than recoded on earth and three times stringer than those on Jupiter. Voyager 2 observed a massive storm that was approximately the size of earth, and a storm was observed that lasted for hundreds of years as a spot on the surface (Lindel, 1992).

3.2

Characteristics

Neptune has a mass that is 17.15 times the mass of earth at 102,410,000,000,000,000 billion kg, the equatorial diameter is 49,528 km, and the polar diameter is 48,682. The circumference at the equator is 155,600 km, with the planet having an ellipticity of 0.01708 (Williams, 2014). The mean density of the planet is 1638 km3. The planet has a ring system, with 5 known rings, the three major rings are names after the official discovers; the Adams Ring, the Le Verrier Ring, and the Galle Ring. Neptune also has 14 known moons, although only one is spherical (Williams, 2014). A day on Neptune (one full planet rotation) is 16 hours.

3.3

Neptune's Orbit

Neptune's mean orbital distance is 30.10 AU, or 4,498,396,441 km, with the perihelion (shortest distance to the sun) at 29.81 AU and aphelion distance (furthest fro the sun at 30.31 AU (Williams, 2014). The orbital period is 164.79 earth years (Williams, 2014). The mean orbital velocity is 5.43 km/s, the maximum is 5.5 km/s and the minimum is 5.37 km/s, and an orbital inclination of 1.769 degrees (Williams, 2014). There is an orbital eccentricity of 0.0085858 (Williams, 2014)

3.4

Comparison to Earth

Neptune is a mach larger planet; it is 17.15 times the earth in terms of mass, and 57.74 times the size of earth in volume. The equatorial radius is 3.883 times the size of earth, whole the polar radius is 3.829 larger. The mean density…