EOSC Lecture 20 The Universe and Solar System

Kilo anum (Ka)

1,000 years

Mega anum (Ma)

1,000,000 years

Giga anum (Ga)

1,000,000,000 years ago

Universe

all existing matter and space; the cosmos

• over 2 trillion observable galaxies

Galaxy

gravitationally bound system of stars, interstellar gas, and matter

100-400 billion stars in the Milky Way

Solar system

gravitationally bound system of a star and all objects that orbit it

• our solar system is relatively young and formed only ~4.6 billion years ago

• our galaxy formed 10-12 billion years ago

• the Big Bang occured ~13.77 billion years ago

• out solar system has formed in only the last ~38% of our galaxy’s history

Expanding universe theory

• current model of our universe

• this means that the universe must have started at a singularity of infinite matter and density which was set into motion by the Big Bang

• Edwin Hubble realized that the light spectrum of galaxies as seen from Earth is either red-shifted or blue-shifted (violet is tight wavelength → red is stretched wavelength)

• wavelengths are either red shifted or blue shifted because of the doppler effect

• almost all galaxies are red shifted and moving away from us

• the further away they are, the faster they are moving away

• this is interpreted as space expanding itself

Doppler effect

when an object moves away from us, the waves (light and sounds) are stretched (therefore perceived as red), when an object moves towards us, the waves are compressed (therefore perceived as blue)

The fate of the universe

the future of the universe depends on the balance of expansion and gravity which pulls things together

• heat death or big chill

• in 4.5 billion years the Andromeda galaxy will collide with the Milky Way

Light years (ly)

• distance in space is measured in light years

• this is the distance light travels in one year

• light has a finite speed

• light travels at approximately 300 million m/s

• in one years light travels ~9.5 trillion km

• looking through space is looking through time

Planetary accretion

• disk of gas and dust spinning around the young sun

• dust particles coalesce (clump) into planetesimals (baby planets)

• planetesimals grow to become protoplanets by colliding and collecting other matter

• eventually they have a clear path of orbit and are plantes

Planet requirments

• it must orbit a star (in our cosmic neighborhood, the sun)

• it must be big enough to have enough gravity to force it into a spherical shape

• it must be big enough that its gravity cleared away any other objects of a similar size near its orbit around the sun

Inner or terrestrial planets

are all rocky and have iron rich cores and silicate rich, solid surfaces

• Mercury, Venus, Earth, and Mars

Mercury

smallest planet, closest to the sun, hot, intense solar winds, no atmosphere

Venus

similar to Earth in diameter, dominated by volcanic landforms, complex mountainous areas, thich C02 rich atmosphere “greenhouse planet”

Earth

active plate tectonic, liquid water at surface, nitrogen and oxygen dominated atmosphere, life

Mars

frozen C02 ice-caps, evidence for liquid water in the past, thin C02 rich atmosphere, cold and dry

• no liquid iron core

• 8 successful unmanned landings with data sent back to Earth

• 10 successful orbiting spacecraft and 5 flybys

Outer or Jovian planets

are all gas (or ice) giants, have ring systems (though only Saturn’s is very obvious) and have many natural satellites (i.e. moons)

• Jupiter, Saturn, Uranus and Neptune

Jupiter

largest planet in the solar system (2.5x the mass of all the other planets combined) composed dominantly of hydrogen and helium, no solid surface, bands and storms ‘Great Red Spot’

Saturn

prominent ring system (ice, rocks and dust) 274 known moons, rocky core, metallic hydrogen layer giving a magnetic field, ammonia in atmosphere giving the yellow colour

Uranus

ice giant, rocky/icy interior, atmosphere contains H, He, H2O, ammonia and methane, coldest atmosphere in the solar system (-225 degrees celsius) tilted axis of rotation (almost 90 degrees off the other planets)

Neptune

ice giant, rocky/icy interior, atmosphere contains H, He, H2O, ammonia and methane, active visible weather patterns

Asteroids

rock

Comets

dirty ice