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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