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The jovian protoplanets grew large enough (10-15 Earth masses) that their gravity was strong enough to draw in large amounts of gas from the solar nebula. The biggerprotoplanets were able to attract even more gaseous material unto themselves. Because of it's position in the solar nebula, the proto-Jupiter, was able to draw an enormous amount of gas unto itself, and become the biggest of the planets. After ~10 million years, Sun begins nuclear reactions ‣Solar wind becomes strong enough to blow away remaining gas ‣Jovian planets stop accreting H/He gas ‣Young planets and leftover planetesimals remain in disk Astronomers calculate that after ~10 million years the sun became hot and luminous enough to blow away the gas remaining in the solar nebula. Thus, the Jovian planets must have grown to their present size in about 10 million years. The terrestrial planets grew from solids and not from the gas. So, they continued to grow by accretion from solid debris left behind when the gas was blown away. The young solar system would have been filled with planetesimals ‣Many were swept up by the forming planets ‣What about the leftovers? Leftover planetesimals bombarded other objects in the late stages of solar system formation
‣Evidenced by the cratered surfaces of the Moon & Mercury! ‣Period of heavy bombardment ‣Lasted for about 800 million years The Moon’s surface shows the scars of the heavy bombardment Earth’s moon, Mercury, Mars, and most of the moons in the solar system are covered with craters. A few of these craters have been formed recently by the steady rain of meteorites that falls on all the planets in the solar system. However, most of the craters you see appear to have been formed roughly 4 billion years ago as the last of the debris in the solar nebula was swept up by the planets. This is called the heavy bombardment. Outer planetesimals had gravitational interactions with the young Jovians ‣Changed their orbits o‣Totally ejected from the solar system, OR... o‣Ejected them to the far reaches of the solar system, OR... o‣Sent them into the inner solar system to collide with terrestrials Face-on view of the young outer solar system.The objects near Jupiter were scattered out of the solar system, or inward toward the Sun.Those between Saturn and Uranus are believed to have been tossed outward to populate the Oort Cloud. Those beyond Neptune were not significantly affected, and remain today as Kuiper Belt Objects Asteroids and comets are the leXover planetesimals! Asteroids are rocky because they formed inside the frostline Comets are icy because they formed outside the frostline The asteroids seen today are the last remains of those rocky planetesimals. Icy planetesimals ejected to the far reaches of the solar system form the Oort Cloud, a spherical distribution of trillions of icy planestimals perhaps 50,000 AUs in diameter.