Wednesday, 24 December 2008
All planets in our solar system, orbit the Sun in the same direction. Unusually for an object in the solar system, comet Halley's orbit is retrograde; it orbits the Sun in the opposite direction to the planets, or clockwise from above the Sun's north pole. Why does Halley choose to be so different?
Planet's complete their orbits in circles around the Sun. However, many comets revolve along more stretched-out ellipses with the Sun near one end instead of in the centre. The point closest to the Sun is the perihelion. There is also a point where the comet is farthest away from the Sun. At this point we say it is at aphelion. Comet Halley is a fine example of a short period comet, taking about 76 years to make one orbit around the Sun. At the perihelion the comet is only 88 million km from the Sun. At the aphelion Halley is 5.2 billion km from the Sun, and thus beyond the orbit of Neptune. This site will give you a far better idea of a comet's journey:
Did you go to the site? Did you see how the comet's tail grew so much longer the nearer it was to the Sun? A comet is thought to be mostly made up frozen ice. This is supposed because 80% of the material ejected by Halley was found to be water. The Giotto space probe found Halley's surface to be rich in carbon. The nucleus of Halley's comet, is in-fact one of the darkest objects in space. This is why American astronomer F.Whipple proposed a hypothesis on the comet nucleus being a "dirty-ice-ball".
The matter which makes up a comet is relatively small. Halley is peanut shaped, 15 km long, 8 km wide and 8 km thick. It's the enormous, bright 'fuzzy patch' which makes comets so visible. As the comet draws nearer to the Sun, the freed gas and dust particles form a cloud or 'halo' around the comet which astronomers call a coma. A comet's coma can get as large as 100, 000 km across as the comet nears the Sun. Not all the material liberated from the comet iceberg remains in the coma. Gas particles sweep out into a long tail pointing away from the Sun. In addition, the dust particles in the outer coma are pushed into a gentle curving dust tail. Comet tails can stretch out for more than 10 million km, yet they contain so few particles in total that the material in a comet tail could easily fit into an average suitcase - and leave enough room for a change of clothes.
Scientific opinion is that the coma and tails are formed by particles being released by the heat of the Sun, and also by the flow of high speed particles from the Sun (known as solar wind). I'm searching for evidence of a more electric relationship.
Comets that reach their aphelion become pretty dim objects out in space. The comets burn brighter the nearer they are to the sun. This then would suggest that the comet offers a higher resistance to the electric current as it draws closer to the Sun. Your normal household lightbulb does the same thing. An incandescent lamp works by the filament resisting the electricity; the resistance makes the filament heat to a high temperature; the heated filament then radiates light. If we wanted a far more brilliant flame of light to match that of our comet, then perhaps we should take a look at the carbon arc lamp.
An arc lamp produces light by the sparking (or arcing, from voltaic arc) of a high current between two carbon rod electrodes. The relatively high resistance to electric current in the gap region, causes the electrode tips to heat to incandescence and emit a brilliant light. I'm imagining our comet as one of these carbon rods. The carbon vaporizes as it works. Also, Swan bands are a characteristic of the spectra of carbon stars, comets and of burning hydrocarbon fuels. This vaporisation of carbon might help explain a comet's dust tail.
A hydrogen gas envelope surrounds the coma of the comet and trails along for millions of miles (it is usually between the ion tail and the dust tail). The hydrogen envelope is about 10 million km across at the nucleus of the comet, and about 100 million km long.
The comet Hale-Bopp, observed in March 1997, has a similar composition to Halley. A third tail (between the dust and the ion tails) of the comet , 50 million km in length, was found to consist largely of sodium atoms. Sodium chloride being an important component of sea water - salt.
On burning in air, magnesium produces a brilliant white light. From electrolysis magnesium chloride produces magnesium. Magnesium is found in over 60 minerals. Dr. Joseph Nuth, Supervisory Astrophysicist at NASA's Goddard Space Flight Center, made observations in 1989, that found crystalline olivine dust (forsterite Mg2SiO4) in comet Halley. The mineral olivine is a magnesium iron silicate.
In a simple experiment with electrolysis where the electrodes are coated with platinum, it is found that when the battery is removed, the reaction reverses. The platinum acts as a catalyst allowing the hydrogen and oxygen to recombine. These electrodes can also be made from carbon.
Instead of putting electricity into the cell to split the water, hydrogen and oxygen combine to make water again, and produce electricity. Eventually this reaction comes to an end, but it shows a very simple way of storing energy. Could this process explain why Halley's journey is so far out at its aphelion? Even though the comet no longer draws a current from the Sun, perhaps it has to wait until all its stored energy is spent, before it is attracted back once again.
So why is Halley's orbit opposite to the direction of the planets in the solar system? There's no gravity in the electric Universe - only magnetic fields. Diamagnetism is the property of an object which causes it to create a magnetic field in opposition of an externally applied magnetic field, thus causing a repulsive effect. It is a form of magnetism that is only exhibted by a substance in the presence of an externally applied magnetic field. Diamagnetism is generally quite a weak effect in most materials, although superconductors exhibit a strong effect. Superconductivity is characterised by exactly zero electrical resistance.
The Earth is thought of as a diamagnet. It is behaving then in opposition to the applied magnetic field. All the other planets in the solar system would therefore also appear to be diamagnets. The planets all orbit the Sun in the same direction as the Earth. Water is highly diamagnetic. If a comet was made up of water, you would expect it to behave purely as a diamagnet. Halley's orbit works in direct contrast to all other planets. A diamagnet is repelled by a magnet. Paramagnetism works in the opposite way, and is attracted to the applied magnetic field.
Paramagnetism is a kind of magnetism characteristic of materials weakly attracted by a strong magnet. Most elements and some compounds are paramagnetic. What relationships, if any, have the paramagnetic, and diamagnetic materials formed onboard Halley's comet?
Many thanks to all the following for their knowledge and insights: