Comets reservoir

After planetary accretion was complete there remained two groups of surviving planetesimals, the comets and asteroids. These populations still exist and play an important role in the Earth s history. Asteroids from the belt between Mars and Jupiter and comets from reservoirs beyond the outer planets are stochastically perturbed into Earth-crossing orbits and they have collided with Earth throughout its entire history. The impact rate for 1 km diameter bodies is approximately three per million years and impacts of 10 km size bodies occur on a... 

A new reservoir of comets may have formed at around 5 AU in a local orbit around Jupiter or at least perturbed by its gravitational attraction. A comet close to Jupiter would simply have been captured, delivering its chemical payload to the ever-increasing gas giant. Some comets would merely have been deflected towards the inner terrestrial planets, delivering a similar payload of water and processed molecules. Cometary impacts such as the spectacular collision of the comet Shoemaker-Levy 9 with Jupiter would have been common in the early formation phase of the solar system but with a much greater collision rate. Calculations of the expected collision rate between the Earth and potential small comets deflected from the snow line may have been sufficient to provide the Earth with its entire... 

Isotope variations found in extraterrestrial materials have been classified according to different processes such as chemical mass fractionation, nuclear reactions, nucleosynthesis, and/or to different sources such as interplanetary dust, solar materials, and comet material. Various geochemical fingerprints point to the reservoir from which the planetary sample was derived and the environment in which the sample has formed. They can be attributed to a variety of processes, ranging from heterogeneities in the early solar nebula to the evolution of a planetary body. For more details the reader is referred to reviews of Thiemens (1988), Clayton (1993, 2004), and McKeegan and Leshin (2001). 

Comets are surviving members of a formerly vast distribution of solid bodies that formed in the cold regions of the solar nebula. Cometary bodies escaped incorporation into planets and ejection from the solar system and they have been stored in two distant reservoirs, the Oort cloud and the Kuiper Belt, for most of the age of the solar system. Observed comets appear to have formed between 5 AU and 55 AU. From a cosmochemical viewpoint, comets are particularly interesting bodies because they are preserved samples of the solar nebula s cold ice-bearing regions that occupied 99% of the areal extent of the solar nebula disk. All comets formed beyond the snow line of the nebula, where the conditions were... 

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. 

The potential components that might have delivered volatile elements to the Earth are the PSN (the major reservoir in the Solar System) and solid matter bodies such as meteorites and comets. The composition of meteoritic volatiles is thought to have been derived from the PSN through elemental and isotopic fractionation. Contributions from sources outside the Solar System such as pre-solar grains or species affected by interstellar chemistry are attested by the discovery of pre-solar grains in primitive meteorites on one hand, and by the large variation of the D/H ratio in the Solar System on another hand, but their extent is a matter of debate. A comparison of the abundances of... 

Information on the chemical composition of active comets is available from two different "reservoirs , viz. solid debris and sublimated volatile species. The former is extracted by IR spectroscopy of the dust tail and dust trails in the comet s orbit, from collected IDPs, possibly a fraction of CI carbonaceous meteorites, and from meteor data. Information on species in the comet coma and plasma tail is obtained by UV-VIS-IR spectroscopy and radio astronomy. 

To date, there exists very little quantitative information concerning oxygen isotope compositions in major solar system reservoirs that is obtained by remote (spectroscopic) observation or spacecraft measurements. A measurement of water ice from comet P/Halley, made by the Giotto mission, yields = 12 75 %o (Balsiger et al. 1995 Eberhardt et al. 1995) but no measurement of is available. Precise data are obtained for the Moon, of course, from returned Apollo samples, and the oxygen isotope composition of Mars and the largest asteroid, Vesta, may be inferred from laboratory... 

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... 

At the same Liege conference, Oort (1950) proposed the existence of a large reservoir of nuclei of comets at a distance of, according to most recent estimates, about 30000 to 50000 AU. This assemblage of nuclei is now known as the Oort cloud. Oort s prediction was based on a study of 19 highly elliptical orbits of new comets - that is, comets that enter the inner Solar System presumably for the first... 

There is no clear distinction between comets and asteroids. Very old comets have lost all their volatiles and the nucleus resembles to asteroids. There are more than 3500 reported known comets which certainly is only a tiny fraction of the whole comet population in the solar system. The main reservoir of comets is in the Oort cloud and there may be several 10 cometary like objects there. 

Water is one of the basic elements for life. It is even assumed that the evolution of life is only possible if there is liquid water present. A water molecule has some remarkable properties that make it quite unique in the universe. In the first chapter of this book we will review these basic properties of water and the role of water on Earth. All ancient civilizations realized the importance of water and their cities were constructed near great reservoirs of water. But is water unique on Earth Do we find water elsewhere in the solar system, on extrasolar planetary systems or in distant galaxies We will start the search for the presence of extraterrestrial water in our solar system. Surprisingly enough it seems that water in some form and sometimes in only minute quantities is found on any object in the solar system. Even on the planet nearest to the Sun, Mercury, there may be some water in the form of ice near its poles where never the light of Sun heats the surface. And there are objects in the solar system that are made up of a large quantity of water in terms of their mass, like comets and several satellites of the giant planets. 

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