Tail, of comet

It has been known for many years that hydrocyanic acid molecules are found in interstellar space and in the tails of comets. The question thus arises as to whether there is a connection between the immense importance of adenine in living beings and the occurrence in the cosmos of a building block for its formation. 

Although the photon has no mass at rest, its inertial mass m = hv/c2 gives a linear momentum of mt. Experimental evidence for this linear momentum is found in the observation of recoil electrons in Compton scattering, or on a much larger scale in the solar wind which blows the tails of comets away from the sun. (It should not be forgotten that material particles also contribute to the solar wind.)... 

Another meteor shower known as the Leonid occurs every year in November, caused by the tail of comet Tempel-Tuttle, which passes through the inner solar system every 32-33 years. Such a year was 1998 on November 17 and 18, 1998, observers on Earth saw as many as 200 meteors an hour. The shower was so intense that it generated widespread concern about the dismp-tion of global telecommunications and the possible damage or destmction of space telescopes. Partly as a result of careful preparation by satellite and telescope engineers, however, concerns afpeared to be minimal. 

The era of space travel has provided astronomers with a valuable new tool for the study of comet structure, composition, and behavior. During the two-year period 1985-86, no fewer than six spacecraft made flybys of comets. The first of these was NASA s ISEE-3 (International Sun-Earth. Explorer 3), which after completing its primary mission of studying the Sun was targeted to pass through the tail of Comet Giacobini-Zinner in September of 1985. At that point, it was renamed the International Comet E q)lorer (ICE). ICE also observed Comet Halley from a distance of 17 million miles (28 million km) in March 1986. 

The second of the two tails, the dust tail, consists of tiny particles of matter expelled from the coma and nucleus by the Sun s radiative pressure. This tail is visible only because the particles of which it is composed reflect sunlight. The composition of cometary dust is thought to be similar to that of interstellar dust, but much remains to be learned about this portion of the comet s structure. In April 2003, NASA launched an experiment to obtain better data about the composition and structure of cometary dust. High-altitude research airplanes were flown through the upper atmosphere toward the tail of Comet Grigg-Skjellerup. Special collectors in the planes scooped up samples of the cometary dust. Analysis may take years. 

Stardust, a U.S. National Aeronautics and Space Administration (NASA) spacecraft, used silica gel to collect particles of debris from the tail of comet Wild-2. 

A number of molecules have been detected in the interstellar medium, in circumstellar envelopes around evolved stars, and comae and tails of comets through observation of their microwave, infrared, or optical spectra. The following list gives the molecules and the particular isotopic species that have been reported so far. Molecules are listed by molecular formula in the Hill order. All species not footnoted otherwise are observed in interstellar clouds, while some are also found in comets and circumstellar clouds. The list was last updated in October 2008 and lists 162 molecules (298 isotopic forms). 

Besides the planets and their satellites, the Solar System harbors a large number of smaller objects, ranging from hundreds of kilometers in size down to dust particles. If they consist of solid material and have at least the size of small boulders, they are called asteroids. If they enter the atmosphere of Earth and reach the surface, they are named meteorites. If they are very small and bum up on entry, they are referred to as meteors. If the bodies contain a substantial fraction of ices and develop tails as they come closer to the Sun, they qualify as comets. However, the classifications are not very consistent for example, remnants of the dust tails of comets cause meteor showers, and older comets, once they have expended most of their volatile matter during many passes near the Sun, may not be distinguishable from asteroids. This section is devoted to comets and the next section (7.3) deals with asteroids. 

Both reactions occur in star forming regions. These reaction take place in star and planet forming gas irradiated by far UV or X-rays. The forth form of water has been detected outside the solar system by the satellite mission Herschel Space Observatory with the HIFI instrument (a high resolution spectrometer for the far IR).6 For example Bonev et al., 2002 [37] measured H2O+ in the plasma tails of comets at a wavelength of 615.886 nm. Further earlier observations of H2O+ in other comets (e.g. Halley s comet) are given in that paper. 

Bonev, T., Borisov, G., Ivanova, A. H2O+ ions in the plasma tail of comet Ikeya-Zhang. Publ. Obs. Astron. Beogr. 73, 73-80 (2002)... 

It is probable that the solvents given in the individual reagent monographs are not suitable for all the substances with which the reagent will react. This point should be taken into account especially for quantitative work and the user should make appropriate modifications. In particular, there must be no loss of substance or reaction product by dissolution (formation of comet tails by the chromatographic zones). 

The interstellar dust was shown to contain quinone derivatives as well as oxygen-rich condensed aromatic compounds the quinones were present in both hydrated and carboxylated form. Very little nitrogen was present in the compounds detected. The cometary material, however, contained condensed nitrogen heterocycles. Hardly any oxygen was detected in the solid phase of the cometary dust it possibly evaporates from the tail of the comet in the form of water or oxidized carbon compounds. The authors assume that these analytical results could lead to a reconsideration of the current biogenesis models (Kissel et al 2004 Brownlee, 2004). 

In principle, it is now possible to construct a complete network of interconnecting chemical reactions for a planetary atmosphere, a hot molecular core or the tail of a comet. Once the important reactions have been identified the rate constants can be looked up on the database and a kinetic model of the atmosphere or ISM molecular cloud can be constructed. Or can it Most of the time the important reactions are hard to identify and if you are sure you have the right mechanisms then the rate constants will certainly not be known and sensible approximations will have to be made. However, estimates of ISM chemistry have been made with some success, as we shall see below. 

Many flames show perceptible spectra produced by chemo-luminescence, such as the diatomic molecules CH, C2 and CN in the blue-green cone of a Bunsen burner (7) also known from the absorption spectra of sun-spots and of red stars, and from the emission (probably fluorescence) of comet tails. 

A) Listeria cell with "comet tail" of cross-linked actin filaments. From Kocks et al. (1992) Cell 68, 521-531. Courtesy of Pascale Cossart. 

B) Enlarged section of a thin comet tail of high resolution showing the actin filaments. From Sechi et al.b Courtesy of Antonio Sechi. 

In the 1950 s, three major concepts have brought d isive advances to the physics of comets Oort s model of a distant cometary cloud, Biermann s solar wind theory of tail formation and dynamics, and Whipple s icy conglomerate model of the cometary nucleus. The main ideas of these concepts shall be outlined briefly. 

Whipple Mass losses of several up to 100 tons per second, depending on the comet s size and distance from the Sun, are necessary to explain the observed changes of the periods, and these numbers agree with the gas and dust production rates derived from observations of the spectra and of the brightness distribution in the comas and tails of some bright comets. 

In fact the method may be strong in getting information on neutrons in comets, and in fact at our laboratory a mass spectrometer probe for the cometary mission of Halley s comet is prepared. But the scenario is a little bit different. Of course the gas tail of the comet has a very complex chemistry and you have gradients in concentrations and change in direction with the radiation field, that the ultimate goal would be to trace back the so-called OH. In order to get these, of course you have to translate or to imravel the entire chemistry — you measure a gas constituent which was produced by possibly not very well known processes. You have to evaporate first the material from the comet, then it is exposed to the UV radiation field of the sun, it s processed photo-chemically, it may undergo some reactions, so that would be very difficult. But there is a chance to get some information. 

This is a kind of Kyoku attached to a shell which displays effects on the trajectory. The word "Do" means here a trajectory. A silver tail, small flowers, comets, thunder, whistles etc. are commonly used as the Kyoku-do. The prefix "Ascending" is used, e.g. "Ascending silver tail", "Ascending comets" etc. 

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