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Chapter 3

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GEOG 1410
Paul Delaney

Life Beyond Earth (Chapter 3) Since Newton: -The universe is vast and old! Implying an enormous number of worlds on which life might possibly have arisen and the time for it to evolve. -The elements of life are widespread: carbon and long chain organic molecules (raw material) have been detected through the galaxy. -Physical laws seem universal: the process that evolved life on Earth could occur anywhere. Our “comic address” is –Earth is a planet in our Solar System –Solar System in our galaxy, Milky Way –Our galaxy in Local Group –The Local Group is in the Local Supercluster –All a part of the universe The scale of our solar system: -The Earth is 1 A(stronomical) U(nit) from the Sun, 150 million kilometers. Beyond the Solar System: to the stars! -A light year (ly) is the distance a photon of light will travel in a year. (10 trillion km) -The seconds in a year: –60 x 60 x 24 x 365.25 -The speed of light: 300, 000 km per second -Thus the distance light would travel in a year is 60 x 60 x 24 x 365.25 x 300, 000 or 12 -9.46 x 10 km!!! Alpha Centauri: our closest star system -4.3 light year to Alpha Centauri (α Cen) -If 1 AU = 1 metre, then α Cen = 271 km! -Our fastest spacecraft leaving the Solar System, Voyager 2 (50,000 km per hour)- would take about 100, 000 years to get there! -Our technology is far too “primitive” to consider trips to the stars at this time. The content of the universe -100,000 ly across and home to ~200 billion stars and a lot of Dark Matter. The universe contains ... -The universe contains all of the matter and energy in existence. -Matter that you would ‘recognize” (planets, stars, etc.), so called baryonic matter: 4% -Dark matter cannot be seen but does have a gravitational influence: 23% -Dark energy (vacuum energy) cannot be seen but manifests itself as a “repulsive- force”: 73% -The more massive is the galaxy the stronger is the gravity and the faster stars should be orbiting. -Dark matter and energy are the biggest mysteries in Astronomy. 3 The Big Bang: 13.8 billion years ago • Observational evidence supports strongly that the universe was once compressed into a very hot, very dense point and that since that time the universe has continued to expand. – Galaxy motion is (by and large) away from the Milky Way – The cosmic mircowave background radiation is the left over “echo” of the universe’s hot beginnings – The distribution of the chemical elements has 
 changed with time, notably H and He initially. Galaxies act as cosmic recycling plants -Stars are created in galaxies by the collapse of clouds of hydrogen and helium. -Stars release energy as a result of nuclear fusion- the process in which light weight atomic nuclei smash together and stick (or fuse) to make heavier nuclei. For example, the formation of helium from hydrogen. -As a star progresses throughout its life heavier elements can be generated. -More massive stars live for shorter periods of time but make (fuse) heavier elements. -Stars can “die” quietly or with great fanfare as in supernovae explosions. -This releases processed material back into the interstellar medium for “reuse” into new stars and planetary systems -Observable Universe: The portion of the entire universe that we can potentially observe, which is only 14 billion years Life beyond earth -Despite the claims of most science fiction films, TV series and books, it would seem highly unlikely given the timescale of the universe for other civilizations to be at the same technological level of advancement as ourselves. -More likely they are enormously more evolved or have long since perished! In either case, evidence likely exists! The Observable universe -The further away an object is from us the further back in time we are looking. -We can only observe as far as light has traveled in the age of the universe, namely 13.8 billion light years Two major types of planets: Terrestrial (Earth-like) Planets: -Mercury, Venus, Earth, Mars are under this category -Relatively small diameters -Relatively high densities, rock and metals composition -Solid Surfaces -Smaller size and mass -Orbit close to the Sun (warmer surfaces) -Thin (if any) atmospheres (carbon dioxide, 
 oxygen, water vapour, etc) -Few (if any) satellites (moons) -No ring systems Jovian or Gas-giant Planets: -Jupiter, Saturn, Uranus, Neptune are in this category -Relatively large diameters -Relatively low densities, mostly gaseous composition (hydrogen, helium, hydrogen compounds) ex; water or methane or ammonia -Larger size and mass -Orbit further from the Sun (colder surfaces) -No solid surfaces -Thick, substantial atmospheres -Many satellites (moons) -Ring systems Other bits and pieces Dwarf planets, asteroids (minor planets) and comets: are also very common components in the Solar System. All “resemble” very small terrestrial planets with comets having a higher “volatile material” (gases) content that allow them to develop beautiful tails. -Dwarf Planets: Ex; Eris, Pluto or other objects large enough for their own gravity. -Asteroids: made up of mostly metal and rock. -Comets: made up of rock and ice. -Asteroid Belt: Most asteroids orbit in the region. -Comets come from two vast reservoirs: Kuiper Belt-Extends from about 30-55 AU, Contains about 70,000 comets more than 100km across. Oort cloud- Extends out to about 50,000 AU, Contains about a trillion comets, Comets orbits have random tilts and eccentricities. Medium and Large Moons: -Enough self-gravity to be spherical -Have substantial amounts of ice -Formed in orbit around jovian planets -Circular orbits in same direction as planet 
 rotation Small Moons: -Far more numerous than the medium and large moons -Not enough gravity to be spherical: “potato- shaped” Why do worlds come in different types? Formation of our solar system: -Nebular Theory: Its stars with the idea that our solar system was born from the gravitational collapse of an interstellar cloud, or nebula, of gas and dust. -Particular cloud that gave birth to our own solar system is usually called the solar nebula. Steps in which solar system was formed (Nebula System): Contraction, Condensation, Accretion, Clearing. Formation of the Solar System -Giant molecular cloud of dust and gas, the solar nebula, begins to spin and collapse -As material moves “inwards”, the proto-Sun begins to form at the centre (warm to hot) -Small planetesimals form and accretion (“stickling together”) of material commences -Small, rocky planets form close to Sun and larger gas planets grow in cooler regions further out The Sun starts to “shine” (nuclear fusion starts) & the solar wind clears out remaining dust & gas. The Law
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