Collisions with Comets

Collisions between comets and planets have occurred often during the evolution of the solar system. Cometary impacts on early Earth may have deposited a substantial amount of water to the Earth. The masses of lost and retained water after the impacts of comets and asteroids on oceans of various depths were studied by Svetsov, 2009 [330], The bombardment of an atmosphereless planet by fast asteroids can wipe out the most part of an ocean. Because of their mass loss during perihelion passage, it is difficult to predict cometary orbits with high precision. Therefore an impact of a comet on a planet cannot be predicted precisely. 

Due to the gravitational influences of planets, comets may even break up into several pieces. Comet Shoemaker-Levy 9 broke up into pieces and collided with Jupiter in 1994. This spectacular event was observable from Earth with even small amateur telescopes. 

If the comet s path crosses Earth s path, then at that point meteor showers are observable as the Earth passes through the trail of debris. The Perseid meteor shower occurs every year between August 9 and 13 when the Earth passes through the orbit of the comet Swift-Tuttle. Halley s comet is the source of the Orionid shower in October. 

Many comets were detected with the solar satellite SOHO (sungrazing comets), they approach the Sun to within several 10 km or even closer and some of them become evaporated during this approach others may survive several passages. 

The loss of the surface layers of comet nuclei was investigated by Thomas, Alexander and Keller, 2008 [334], Their conclusion is that local variations in out-gassing rates can be substantial, subsurface sublimation down to a depth of 2.3 cm. 

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An internal one by gas emission after accretion of the Earth, and An external one, via collisions with comets and asteroids which contained... 

Since the SN was unlikely the major contributor to the earth s atmosphere, one may consider the following contributors (1) collision with comets, (2) volatilization of impacting material and (3) outgassing. One may distinguish two periods of outgassing. While the accretion energy due to impact was in principle sufficient to melt the entire Earth, this... 

The elastic bounce cannot occure in actual astronomical phenomena. A nonelastic collision must occure. For instance, remember the comet Shoemaker-Levy collision with Jupiter in 1994. 

Kaiser, R.I. Ochsenfeld, C. Head-Gordon, M. Lee, Y.T. Suits, A.G. A combined experimental and theoretical study on the formation of interstellar C3H isomers. Science 1996, 274, 1508-1511. Kaiser, R.L Ochsenfeld, C. Head-Gordon, M. Lee, Y.T. Neutral-neutral reactions in the interstellar medium. IL Isotope effects in the formation of linear and cyclic C3H and C3D radicals in interstellar environments. Astrophys. J. 1999, 510, 784—788. Kaiser, R.L Ochsenfeld, C. Head-Gordon, M. Lee, Y.T. The formation of HCS and HCSH molecules and their role in the collision of comet Shoemaker-Levy 9 with Jupiter. Science 1998, 279, 1181-1184. Kaiser R.L Stranges D. Lee Y.T. Suits A.G. Neutral-neutral reactions in the interstellar medium. 1. Formation of carbon hydride radicals via reaction of carbon atoms with unsaturated hydrocarbons. Astrophys. J. 1997, 477, 982-989. 

Such hypotheses are confirmed in two ways. One is the discovery of precursors to complex biochemical molecules already detected in comets, such as those listed in the chart on page 189. The other is through laboratory experiments that test (1) whether the organic molecules found in comets can survive collision with Earth and, if so, (2) whether they can then evolve into more complex molecules from which life can develop. 

Since in its early history the earth was too hot for liquid water to exist, it has been theorizedthat all of the water on the earth came from collisions of comets with the earth. Assume an average diameter for the head of a comet and assume that it is completely composed of water ice. Estimate the volume of water on the earth and estimate how many comets would have collided with the earth to supply this much water. 

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... 

Other events, evidence of which has not yet been detected in polar ice, may also eventually serve as useful time markers in the future. Large meteors or meteor swarms that ablated in the upper atmosphere may have left a significant chemical impact on succeeding snowfalls. The same may be true for cometary collisions or brushes with a comet s tail. As with ancient volcanic eruptions, such events need not have been historically documented. If identified and accurately dated in one ice core, these events will serve as useful time horizons in other cores. 

The Earth and other planetary bodies have been heavily modified by planetary-scale differentiation, smaller scale melting and the resulting chemical fractionations, collisions that mix material with different histories, and other processes. Samples of these materials are thus not suitable for determining the solar system composition. More primitive objects, such as comets and chondritic meteorites, have compositions more similar to the composition of... 

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