Comets long period

Long-period comets their extended ellipsoidal orbits reach far outside our solar system (up to half the distance to the next fixed star). This group includes the comet Kohoutek, discovered in the 1970s, which requires about 75,000 years for a single orbit. 

The source of long-period comets is thought to be the Oort cloud (Weiss-mann, 1998). 

Fine structure on the silicate feature provides more specific mineralogical information. A small bump at 11.2 pm on the 10 pm feature (Fig. 12.4a), observed for several long-period comets, is generally interpreted as indicating crystalline olivine. Another shoulder at... 

Oort cloud (Oplk-Oort cloud) A spherical cloud of comets that is believed to surround the entire solar system and provide a reservoir of long-period comets. It is estimated to contain up to 10 comets and to extend from between 2000 and 5000 astronomical units (AU) to 50 000 AU from the sun. Disturbances caused by a passing star push comets into eccentric solar orbits that may bring them to the inner solar system or else eject them from the solar system altogether. It is... 

Already in 1932 E. Opik assumed that long-period comets originate in a cloud at very large distance from the inner solar system. Since the long-period comets have random orbits, such a cloud must be distributed spherically around the solar system. Oort, 1950 [255] postulated its existence from the volatile composition of comets and their orbits (see Fig. 5.2). He found a peak in the numbers of nearly isotropic distributed comets with apheUa of roughly 20 (X)0 AU. 

The Oort cloud is the source of long period comets. Especially the objects in the outer cloud are only loosely bound to the Solar System and can be easily disturbed... 

Long period comets they have eccentric orbits with periods greater than 200 years. Their orbital periods can extend several 10 up to 10 years. However, they are not on a parabolic orbit which means that they are still gravitationally bound to the Sun. Their plane of orbit may be highly inclined with respect to the... 

The icy objects in the Kuiper belt and Oort cloud become ejected into the inner solar system where they appear as comets. Perturbations by outer planets occur in the Kuiper belt, these become short period comets, perturbations by nearby passing stars affect objects in the Oort cloud, these become long period comets. 

Levison H. F. and Duncan M. J. (1994) The long-term dynamical behavior of short-period comets. Icarus 108, 18-36. 

Comets can be classified into two major groups short-term and long-term comets. Short-term comets are those with orbital periods of less than 200 years. They can be further subdivided into two groups the Jupiter family, with periods of less than 20 years, and... 

Which results led to the idea that comets are important in the evolution of life For more than ten years, some scientists have believed that life has (possibly) existed on Earth for more than 3.5 billion years recently, however, doubts have arisen as to whether this is really the case. It does seem clear that the heavy bombardment of the primeval Earth slowly started to decrease about 3.8 billion years ago. Many biogenesis researchers believe that a period of about 300 million years after the bombardment ceased would not have been long enough for life to evolve from inanimate systems. Thus the idea that comets (or perhaps even meteorites) played a role in the biogenesis process on Earth is quite appealing. Three possibilities are under discussion ... 

Comets are not stable near the Sun and they are short lived in regions of the solar system where they exhibit cometary activity. Active comets are derived from two major reservoirs where they can be stored in adequate long-term isolation from solar heating and planetary perturbations. These reservoirs are called the Oort cloud and the Kuiper Belt. It appears that virtually all comets with low-inclination orbits with orbital periods less than 30 yr are derived from the Kuiper Belt while others come from the Oort cloud. 

Newton showed that, under the inverse-square attraction of gravitational forces, the motion of a celestial object follows the trajectory of a conic section. The stable orbits of the planets around the sun are ellipses, as found by Kepler s many years of observation of planetary motions. A parabolic or hyperbolic trajectory would represent a single pass through the solar system, possibly that of a comet. The better known comets have large elliptical orbits with eccentricities close to 1 and thus have long intervals between appearances. Halley s comet has e = 0.967 and a period of 76 years. 

The most prominent and most intense transition is the triplet system A ITj t- X Z with its maximum around 336 nm. It has been known for a long time and extensively analyzed over a period of almost 60 years. Since it is the chief characteristic of the NH radical, the spectrally or temporally resolved A X system has been repeatedly used to prove the existence of the radical and to monitor its formation and decay processes in various environments, such as N- and H-containing gas molecules in electric discharges or during photolysis or radiolysis, molecular beams, flames, or noble-gas matrices. The A< X spectrum even proved the existence of NH in the sun, in stellar atmospheres, and in comets. 

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