Neptune, the solar sytem's furthest gas planet, is thirty(30) times further from the sun than the Earth. It is tne smallest gas planet in our solar system and also the densest of the 4 giant planets. This planet receives only about 3% as much sunlight as Jupiter. Its diameter at the equator is 49, 500 kilometers. Neptune orbits the sun every 165 years. It has 8 moons, six of which were found by Voyager. It was Voyager 2, in the summer of 1989, that became the first spacecraft to observe Neptune. A day on Neptune is about 16 hours and 6.7 minutes. Neptune was discovered by Johann Gottfried Galle, a scientist at the Berlin Observatory, and Louis d'Arrest, an astronomy student, through Urbain Jean Joseph le Verrier's mathematical predictions, on September 23, 1846.
The planet is composed in its first two-thirds, of a mixture of molten rock, water, liquid ammonia and methane. The outer third is composed of a mixture of heated gases comprised of hydrogen, helium, water and methane. Methane, which absorbs red light, is what gives Neptune its blue color.
Like that of Uranus, the magnetic field of Neptune, is highly titled at 47 degrees from the rotation axis and offset at least 0.55 radius, which is about 13,500 kilometers from the physical center. By comparing the magnetic fields of these planets, scientists think that the extreme orientation may be a characteristic of lows in the interior of the planet, not the result of that planet's sideways orientation or of any possible field reversals of either planet.
A typical day on Neptune exhibits highs in the upper atmosphere of about 150 degress centigrade. Winds range fom about 900 mph near the equator. Long bright clouds which are similar to that of cirrus clouds on Earth, can be seen high in Neptune's atmosphere. The yellow spots are the highest clouds. Cloud streaks cast their shadows on cloud decks below at low northern latitudes. The strongest winds ever measured on any planet were on Neptune. Most of the winds blow westward, which is opposite the rotation of the planet.
Neptune is a planet with many large, dark spots that are reminiscient of Jupiter's hurricane-like storms.
The planet's Great Dark Spot is about the size of the earth. It is similar to Jupiter's Great Red Spot and comparible in size at the same relative south latitude. This dark spot consists of feathery white clouds that fill the boundary between the dark and light blue regions of it. The storm system's counter-clockwise movement is suggested by the white arms and the pinwheel shape of the dark boundary. In 1994, the Hubble Space Telescope viewed the planet and the spot had vanished, only to be replaced by another dark spot in it's northern hemisphere.
In June, 1994, the Hubble Space Telescope revealed that the Great Dark Spot found by Voyager 2 was missing. A new spot near the limb of the planet has formed. This new spot has high altitude clouds along its edge, which are caused by gasses that are pushed to higher altitudes where they cool to form methane ice crystal clouds. The dark spot may be a zone of clear gas that is a window to a lower cloud deck in the atmosphere.
This small spot is thought to be a storm in Neptune's atmosphere, which may be similar to Jupiter's Great Red Spot.
| Characteristic | Measurement |
|---|---|
| Mass (kg) | 1.024e+26 |
| Mass (Earth = 1) | 1.7135e+01 |
| Equatorial radius (km) | 24,746 |
| Equatorial radius (Earth = 1) | 3.8799e+00 |
| Mean density (gm/cm^3) | 1.64 |
| Mean distance from the Sun (km) | 4,504,300,000 |
| Mean distance from the Sun (Earth = 1) | 30.0611 |
| Rotational period (hours) | 16.11 |
| Orbital period (years) | 164.79 |
| Mean orbital velocity (km/sec) | 5.45 |
| Orbital eccentricity | 0.0097 |
| Tilt of axis | 28.31° |
| Orbital inclination | 1.774° |
| Equatorial surface gravity (m/sec^2) | 11.0 |
| Equatorial escape velocity (km/sec) | 23.50 |
| Visual geometric albedo | 0.41 |
| Magnitude (Vo) | 7.84 |
| Mean cloud temperature | -193 - -153°C |
| Atmospheric pressure (bars) | 1-3 |
| Atmospheric Composition | Percent |
|---|---|
| Hydrogen | 85% |
| Helium | 13% |
| Methane | 2% |
| Moon | Number | Radius (km) | Mass (kg) | Distance (km) | Discoverer | Date |
|---|---|---|---|---|---|---|
| Naiad | III | 29 | ? | 48,000 | Voyager 2 | 1989 |
| Thalassa | IV | 40 | ? | 50,000 | Voyager 2 | 1989 |
| Despina | V | 74 | ? | 52,500 | Voyager 2 | 1989 |
| Galatea | VI | 79 | ? | 62,000 | Voyager 2 | 1989 |
| Larissa | VII | 104x89 | ? | 73,600 | Voyager 2 | 1989 |
| Proteus | VIII | 200 | ? | 117,600 | Voyager 2 | 1989 |
| Triton | I | 1,350 | 2.14e+22 | 354,80 | W. Lassell | 1846 |
| Nereid | II | 170 | ? | 5,513,400 | G. Kuiper | 1949 |
Triton is Neptune's largest moon. It has a diameter of 2,700 kilometers. This moon was discovered by William Lassell, a British astronomer, in 1846, barely a month after Neptune was discovered. Triton is the coldest object measured in the solar system because it has a surface temperature of -235 degrees celcius. It has an extremely thin atmosphere. The atmospheric pressure at Triton's surface is about 14 microbars, which is 1/70,000th the surface pressure on Earth.
This moon is the largest satellite in our solar system to circle a planet in retrograde direction(direction is opposite the rotation of the planet). Triton has a density of about 2.066 grams per cubic centimeters. Triton contains more rock in its interior than Uranus and Saturn's icy satellites do. Its relatively high density and its retrograde orbit has led some scientists to suggest that as it traveled through space several billions year ago, it may have been captured by Neptune. Due to this, tidal heating could have melted Triton in its originally eccentric orbit, and the satellite may also have been liquid for as long as one billion years after it was captured by Neptune. Triton is characterized by enormous cracks. Several kilometers into its atmosphere, there are active geyser-like eruptions spewing nitrogen gas and dust particles.
| Name | Distance* | Width | Thickness | Mass | Albedo |
|---|---|---|---|---|---|
| 1989N3R | 41,900 | 15 | ? | ? | low |
| 1989N2R | 53,200 | 15 | ? | ? | low |
| 1989N4R | 53,200 | 5,800 | ? | ? | low |
| 1989N1R | 62,930 | < 50 | ? | ? | low |
Neptune's set of four rings are narrow and very faint. These rings are made up of dust particles which are thought to have been made by tiny meteorites smashing into Neptune's moon. The rings appear to be arcs from ground based telescopes, but from Voyager 2 they turned out to be bright spots or clumps in the ring system. The exact cause of the bright clumps is not known.
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Credits, for research, are due to Voyager, The Hubble Space Telescope, Massachusetts Institute of Technology and NASA. Also many acknowledgements to Lulama Cooper and Mr. Bill Drennon.
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This page was written by Nadine Matthie in the astronomy class of BCC/Broward County, July, 1998. |