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Abstract: A revised linear model is presented to explain the waves from the collisions of Comet Shoemaker-Levy 9 with Jupiter, in which the Jovian atmosphere is taken as a rotating stratified, compressible and inviscid fluid layer. It is shown that the effect of compressibility can not be ignored, although most of the impacting energy is still converted into the energy of internal waves. [Copyright &y& Elsevier]

Abstract: After the collision of Comet Shoemaker-Levy 9 (SL9) with Jupiter, some ring structures were observed propagating outwards at a constant speed (∼450 m/s) on the Jovian surface. These are thought to be linear waves caused by the collision. A linear model of the collision is presented, in which the Jovian atmosphere is considered as an irrotational, inviscid, stratified and incompressible fluid layer moving at a speed of U = b + az. We take an initial impulsive pressure p(r; 0) as the initial condition and solve the fluid dynamics equations for inertia-gravity waves. It is found that most part of the perturbation energy is used to produce internal waves when Jovian atmosphere moves at a constant speed (U = U o (∼170 m/s)). A relation between the impact depth H and the horizontal phase speed vp is deduced. Finally, the inertia-gravity waves are discussed for the case U = b + az and it is found that the perturbation energy is then not divided equally between kinetic energy and potential energy because of the effect of a shear. [Copyright &y& Elsevier]

In this paper, the significance, instrumentality, and the status in the search for extra-terrestrial intelligence, and, in addition, the SETI program and its development, are introduced. Especial emphasis is on the discovery of extrasolar planets, its purpose, ways and means, achievement, and future.Finding extrasolar planets is one of the most popular issues at present. It will be one of the most fruitful research fields in astronomy in the 21st century. Since the first affirmation of an extrasolar planetary system in the pulsar PSR1257+12, and the first discovery in 1995 of a planet in a main-sequence star, 51 Peg, some fifty extrasolar planets have been discovered. The discovery cannot be detached from the search for extra-terrestrial intelligence, and it also opens up new problems. During the past 10 years the research has been developing rapidly. Not only in astronomy, but also in other sciences, like spaceflight, astrochemistry, astrobiology, even in philosophy, it plays an advancing function. [Copyright &y& Elsevier]