الفصل الرابع نشأة المجموعة الشمسية الدكتور عبد القادر عابد الجامعة الأردنية Prof. Abdulkader M. Abed / University of Jordan

Prof. Abdulkader M. Abed / University of Jordan This photograph shows the central region of the Orion Nebula, an interstellar cloud in which star systems–possibly including planets–are forming. The photo is a composite of more than a dozen separate images taken with the Hubble Space Telescope. (See Figure 1.4a for a complete view of the Orion Nebula.) Prof. Abdulkader M. Abed / University of Jordan

Prof. Abdulkader M. Abed / University of Jordan This sequence of paintings shows how the gravitational collapse of a large cloud of gas causes it to become a spinning disk of matter. The hot, dense central bulge becomes a star, while planets can form in the surrounding disk Prof. Abdulkader M. Abed / University of Jordan

Prof. Abdulkader M. Abed / University of Jordan The galactic recycling process Prof. Abdulkader M. Abed / University of Jordan

Prof. Abdulkader M. Abed / University of Jordan Temperature differences in the solar nebula led to different kinds of condensed materials, sowing the seeds for two different kinds of planets. Prof. Abdulkader M. Abed / University of Jordan

Prof. Abdulkader M. Abed / University of Jordan Composition of the Solar Nebula Metals Rock Hydrogen Compounds H2 + He gas Fe, Ni, Al Var. H2O, CH4, NH3 H2 + He minerals 0.2 0.4% 1.4% 98% 1000-1600K 600-1300 k <150K do not condense in nebula Prof. Abdulkader M. Abed / University of Jordan

Prof. Abdulkader M. Abed / University of Jordan These diagrams show how planetesimals gradually accrete into terrestrial planets. Early in the accretion process, there are many Moon-size planetesimals on crisscrossing orbits (top). As time passes, a few planetesimals grow larger by accreting smaller ones, while others shatter in collisions (center). Ultimately, only the largest planetesimals avoid shattering and grow into full-fledged planets (bottom). Diagram not to scale Prof. Abdulkader M. Abed / University of Jordan

Prof. Abdulkader M. Abed / University of Jordan Shiny flakes of metal are clearly visible in this slice through a meteorite (a few centimeters across), mixed in among the rocky material. Such metallic flakes are just what we would expect to find if condensation really occurred in the solar nebula as described by the nebular theory Prof. Abdulkader M. Abed / University of Jordan

Prof. Abdulkader M. Abed / University of Jordan Large icy planetesimals in the cold, outer regions of the solar nebula captured significant amounts of hydrogen and helium gas. This process created solar nebulae in miniature. In our solar system, four of these miniature solar nebulae formed, from which each of the jovian planets and many of their satellites formed. The inset painting (left) is located within the entire solar nebula as shown Prof. Abdulkader M. Abed / University of Jordan

Prof. Abdulkader M. Abed / University of Jordan Around 4 billion years ago, Earth, its Moon, and the other planets were heavily bombarded by leftover planetesimals. This painting shows the young Earth and Moon faintly glowing with the heat of accretion, and an impact in progress on Earth Prof. Abdulkader M. Abed / University of Jordan

Prof. Abdulkader M. Abed / University of Jordan The two moons of Mars, shown here in photos taken by the Viking spacecraft, are probably captured asteroids. Phobos is only about 13 km across and Deimos is only about 8 km across–making each of these two moons small enough to fit within the boundaries of a typical large city. a Phobos. b Deimos Prof. Abdulkader M. Abed / University of Jordan

Prof. Abdulkader M. Abed / University of Jordan Artist's conception of the impact of a Mars-size object with Earth, as may have occurred soon after Earth's formation. The ejected material comes mostly from the outer rocky layers and accretes to form the Moon, explaining why the Moon is poor in metal. Prof. Abdulkader M. Abed / University of Jordan

A summary of the process by which our solar system formed Prof. Abdulkader M. Abed / University of Jordan