Unit 1.1: Planets

SUN

1. Mercury                                                My

2. Venus                                                  Very

3. Earth                                                   Easy

4. Mars                                                    Method

ASTEROID BELT

5. Jupiter                                                 Just

6. Saturn                                                 Speeds

7. Uranus                                                 Up

8. Neptune                                               Naming (planets)

TERRESTRIAL PLANETS

1. Mercury - Heavily cratered surface with signs of volcanism, a weak magnetic field similar to the Earth's, so has an iron-rich core. 

Distance from sun = 0.4 AU    Atmosphere = Thin, mainly helium    Density = 5.43 g/cm3    No. of moons = 0   Mean temp. = -183/427°C

2. Venus - Desert surface & has craters, shield volcanoes and structures resembling lava flows.

Distance from sun = 0.7 AU   Atmosphere = Dense, carbon dioxide and clouds of sulphuric acid  Density = 5.24 g/cm3   No. of moons = 0   Mean temp. = 457/482 °C

3. Earth - 67% oceans, landmasses with volcanoes, high mountains, extensive rivers and lakes, dessert areas and ice caps, few impact craters.

Distance from sun = 1.0 AU   Atmosphere = Nitrogen and oxygen, with variable amounts of water vapour   Density = 5.515 g/cm3   No. of moons  = 1   Mean temp. = 15/20°C

4. Mars - Large shield volcanoes, features which look as if they may have been formed by running water. No running water on the surface today, but there is water trapped in polar ice caps and may also be trapped underground.

Distance from sun = 1.5 AU   Atmosphere = thin, mainly carbon dioxide   Density = 3.933 g/cm3   No. of moons = 2   Mean temp. = -87/-5°C

THE ASTEROID BELT

Asteroids = rocky objects which failed to form a planet when the rest of the Solar System was created.

• Large, rocky objects left over from the formation of the Solar System.
• Fragments of carbonaceous, silicate and metallic material..
• Found between Mars and Jupiter, separating the terrestrial planets with the gas giants.
• Most asteroids are only the size of pebbles.
• Largest asteroid had a diameter of 914km (Ceres).
• Collisions between asteroids result in fragments being broken off. These fragments then travel through the Solar System and some are captured by the Earth's gravity and fall to the Earth's surface as meteorites.

Meteorites = fragments of rock which fall to Earth from space.

A comet = composed of ice and dust. The outer layers melts to water vapour as it gets closer to the sun

The gas giants 

5. Jupiter - Small rocky/ metallic core. Enormous pressures in the core genegrate large amounts of heat, radiation and a powerful magnetic field.

Distance from sun = 5.2 AU   Atmosphere = Hydrogen and helium cloud belts and a large red spot, which is a giant whirling storm of rising gas   Density = 1.33 g/cm3   No. of moons = >60   Mean temp. = -150°C

6. Saturn - Rings composed of icy debris. A rocky core covered by liquid hydrogen.

Distance from sun = 9.5 AU   Atmosphere = Hydrogen   Density = 0.70 g/cm3   No. of moons = >30   Mean temp. = -180°C

7. Uranus - Icy rings and a rocky core.

Distance from sun = 19.2 AU   Atmosphere = Mostly hydrogen, with some helium and methane   Density = 1.30 g/cm3   No. of moons = >20    Mean temp. = -197°C

8. Neptune - Faint ring system. A magnetic field, so probably has a rocky core.

Distance from sun = 30.1 AU   Atmosphere = Mostly hydrogen, with some helium and methane   Density = 1.76 g/cm3   No. of moons = >10   Mean temp. = -200°C

THE BIG BANG

• 14 billion years ago.
• The event that led to the formation of the Universe
• The point in time where all matter and energy were created
• At that moment, all matter was compressed into a space billions of times smaller than a proton.
• Both time and space were set to zero.

THE NEBULA HYPOTHESIS

• 4500 million years ago.
• The Solar System formed when a giant cloud of molecular dust and gas collapsed (possibly when hit by a shockwave from a nearby exploding star (supernova)).
• The material eventually formed a rotating disk and as material was drawn towards the centre it triggered nuclear reactions which resulted in the formation of the Sun.
• Other material in the disk of dust particles began to stick together by a process called accretion. This formed progressively larger objects, finally resulting in the formation of planets.

• Most of our knowledge about the planets has come from space exploration missions.
• Space exploration began in the 1960s with early missions to the Moon, Venus and Mars.
• The Hubble telescope has enabled astronomers to observe the early stages of star formation.

THE MOON

• First soft landing missions were sent to the Moon.
• First manned landing in 1969.
• The Apollo missions brought back 20kg of rock and soil. These rocks were much older than expected with the oldest rocks dating back to 4400Ma.
• The moon has a solid crust, mantle and core, and the surface is made up of:

   - the maria = dark areas composed of basalt lava flows, which were generated by the impact of meteorites.

  - the highlands = light coloured areas composed of a plagioclase-rich rock anorthosite.

MARS - the exploration of Mars has occured in 3 stages:

1) In the 1960s the space probes flew by Mars, taking as many pictures as possible. They identified huge volcanoes including Olympus Mons, (the largest volcanic structure in the solar system).

2) Spacecraft were then put in orbit around Mars for longer-term, global studies. These orbital missions started in the 1970s, and in 2005 the Mars Reconnaissance Orbiter was capable of takinf photos showing objects just 10cm across.

3) In 2007, spacecraft landed on the surface to move around and explore. This will tell us more about the geology of the planet, the prescence of water, and maybe even clues about whether Mars was ever a habitat for life.

VENUS

• Similar in size, mass, composition and distance from the Sun to Earth.
• Spacecraft have landed on Venus and mapped it using radar, so the data on temperature and pressure are actual measurements.
• Has no oceans.
• Covered by thick, rapidly spinning clouds that trap surface heat, creating a scorched greenhouse-like world with temperatures high enough to melt lead.
• The clouds reflect sunlight, making it the brightest planet in our sky.

The Solar System = the Sun, planets, their moons, comets and asteroids.

The Sun = a star composed of hydrogen and helium. The largest object in the Solar System and contains more than 99.8% of the total mass.

A planet = a sizable object orbiting a star.

A moon = a natural satellite orbiting a planet.

METEORITES = fragments of rock, which fall to Earth from space.

• Most meteorites come from the asteroid belt.
• A few are thought ot come from the Moon or Mars.
• Meteorites can be identified as coming from the Moon because they have a composition and age similar to rock samples brought back from the Moon.
• There are 2 types of meteorites.

IRON ~ Composed of an alloy of iron and nickel. 6% of known meteorites are this type. Thought to represent the core of a small planet-like object, which formed early in the history of the Solar System.

STONY (CARBONACEOUS CHONDRITES) ~ Composed of silicate materials including olivine, pyroxene and plagioclase feldspar. 93% of known meteorites are this type. Thought to represent the mantle of a small planet-like objet, which formed early in the history of the Solar System. Similar in composition to the Sun, but with fewer volatiles.

• The impact of asteroids forms distinctive craters, (which you can see on the surface of the moon).
• The craters all have a circular depression and a rim of broken rock. Craters cover most of the moon's surface.
• The Earth's surface does not show such extensive craters though there are some, including the 50 000 year old crater in Arizona.
• There is no reason to assume that the Earth is less prone to impacts than the moon, so there must be another reason...
• The difference is the amount of activity affecting the Earth's surface. The Earth's crust is subject to weathering, erosion and long-term recycling by plate tectonics, all of which destroys craters.

When a crater is formed, the impact causes:

• Material to be ejected and quartz grains to be violently shocked or even melted.

• Rock strata to be tilted.

• Material at depth to be brecciated (broken up)

• The ejected material falls back to the surface, but the sequence of rocks is inverted bacause material closer to the surface is ejected first and falls back to the surface earlier. 

• Volcanic activity is clearly seen on Mars with the huge shield volcanoes like Olympus Mons.
• Venus also has volcanoes.
• These inner planets have a core and rocky mantle like the Earth, so volcanic activity as a result of the heat from the core is to be expected. 

VOLCANISM ON THE MOONS OF THE OUTER GAS GIANTS

• Lo is the innermost moon of Jupiter 
• Is extremely volcanic with evidemce of lava flows covering craters formed early in its history.
• Lo is too small to have its own heat source for the volcanic activity and the heat is thought to be generated by tidal heating - the result of the enormous gravity field of Jupiter.

• The generally accepted age for the Earth and the rest of the Solar System is about 4550 million years (plus or minus 1%).
• The age cannot be measured directly from material on the Eart as the surface was initially molten. Then the processes of erosion and crustal recycling destroyed the original surface.
• The oldest rocks found so far on Earth date to about 3800 Ma to 3900 Ma.
• Some of these rocks are sedimentary and include minerals as old as 4200 Ma. 
• Rocks of this age have been found on North America, Grrenland, Australia, Africa and Asia.

• Uses the dacay of radioactive isotopes.
• To determine the age of an object, we need to know
  • The rate at which the radioactive isotope decays (half-life) - which is determined in a laboratory.
  • The amount of the radioactive isotope that was incorporated into the object when it formed.

• One radioactive isotope that can be used to date planets is Rhubidium-87 (⁸⁷Rb) which decays to Strontium-87 (⁸⁷Sr) with a half-life of 4.88 x 10¹⁰ years.

• Dating rocks is a complex process, so radiometric dates are quoted with a degree of uncertainty, which is usually less than 1%.