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Figure 9.10b: On 21 January 2014, astronomers witnessed the supernova SN 2014J soon after it exploded in the Messier 82 (M82) galaxy. Supernovas signal the destruction of an entire star and can be so bright that they outshine the whole galaxy where they are found. Supernovas inject huge amounts of energy into the interstellar gas, and are responsible for dispersing elements such as iron, calcium and oxygen into space where they may be incorporated into future generations of stars and planets. It is in supernova shocks that all natural elements heavier than iron are created, including uranium, the heaviest natural element found on Earth.


Rubidium 85.4678


Caesium 132.90545196


Francium 223


Rb Cs Fr


Strontium 87.62


Sr


Barium 137.327


Yttrium 88.90584


Y


Radium 226


Ba La–Lu Hf Ra


57–71 Lanthanide


Actinium 227


Ac


Hafnium 178.49


Thorium 232.0377


Lanthanum 138.90547


Th La


9.1.4.2 Creating Planets


Gas and dust with heavier elements swirl around a newly forming second- or third-generation star, like our sun, which was born 4.6 billion years ago, making small pellets which collide to create larger bodies called planetoids. Tese coalesce, forming planets, minor planets, moons, comets and asteroids, with much empty space between them. Once born through the initiation of the fusion process, the stars’ powerful solar winds begin to blow. Tese winds, made up of atomic particles being blown outward from the star, slowly push any remaining gas and dust out of the solar system. With no more gas or dust, the planets stop growing. In the inner system of the star, the solar winds are stronger


than in the outer system, far from it. As a result, less dust and gas is present in the inner solar system. During a short period of 100,000 to 300,000 years, particles have the opportunity to grow into larger and larger rocks and may eventually coagulate into kilometre-sized planetary embryos. Near the star, these go through a stage of violent mergers, producing a few terrestrial planets. Te last stage takes approximately 100 million years. Planets of the outer solar system start as planetary embryos


made of various types of ice and are many times more massive than the embryos in the inner solar system. As they grow larger, their gravity has time to accumulate massive amounts


Zirconium 91.224


Zr


Tantalum 180.94788


Protactinium 231.03588


Ce


Cerium 140.116


Nb Mo Tc Ta W Re Pa


Niobium 92.90637


Molybdenum 95.95


Tungsten 183.84


Uranium 238.02891


U


Praseodymium 140.90766


Pr


Neodymium 144.242


Nd Pm Sm Eu


Promethium 145


Samarium 150.36


Europium 151.964


Gadolinium 157.25


Gd


Terbium 158.92535


Tb


Dysprosium 162.500


Dy Ho


Holmium 164.93033


Erbium 167.259


Er Tm Yb


Thulium 168.93422


Ytterbium 173.054


Lutetium 174.9668


Lu


of gas and ice, as well as dust. Tose which grow to between five and ten times the mass of the Earth will begin accretion of the hydrogen–helium gas from the disc. Te accumulation of gas by the planet core is initially a slow process which continues for several million years. After the evolving protoplanet reaches about 30 Earth masses the gas accretion accelerates and proceeds in a runaway manner. Jupiter- and Saturn-like planets are thought to accumulate the bulk of their mass over only 10,000 years. Te accretion stops when the gas is exhausted.


9.1.5 Our Solar System


A solar system is made up of all bodies that orbit a particular star: planets, moons, comets, asteroids, minor planets, and dust and gas. In our solar system orbiting the centre of the Milky Way galaxy, the star is the sun, which formed 4.6 billion years ago, and which contains as much as 98% of all material. Its gravity attracts the other objects towards it. At the same time, these objects, which are moving very rapidly, try to fly away from the sun. Te result of the objects trying to escape into space while the sun is trying to pull them inward is that they become trapped, spending eternity tracing the sun in elliptical (or in most cases, almost circular) orbits. In our solar system, the planets are of two types. Closest to the sun sit Mercury, Venus, Earth and Mars, all Earth-like


301


Technetium 98


Ruthenium 101.07


Rhenium 186.207


Osmium 190.23


Ru Os


Rhodium 102.90550


Co Rh Ir


Cobalt 58.933194


Iridium 192.217


Ni


Nickel 58.6934


Palladium 106.42


Platinum 195.084


Pd Pt


Cu Ag


Copper 63.546


Silver 107.8682


Gold 196.966569


Cadmium 112.414


Zn Cd


Zinc 65.38


Au Hg


Mercury 200.592


Thallium 204.38


Ga In Tl


Gallium 69.723


Indium 114.818


Germanium 72.630


Ge Sn Pb


Tin 118.710


Lead 207.2


Arsenic 74.921595


Antimony 121.760


Bismuth 208.98040


As Sb Bi


Selenium 78.971


Tellurium 127.60


Polonium 209


Se Te Po


Bromine 79.904


Iodine 126.90447


Br I


Astatine 210


At


Krypton 83.798


Kr


Xe Rn


Xenon 131.293


Radon 222


37 55 87 88 89 90 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 91 92 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 56 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 27 28 29 30 31 32 33 34 35 36


NASA


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