The Solar System

1. The Solar System • A Solar System is made up of one or more stars which emit huge amounts of radiation (visible and invisible) and a number of smaller planets which orbit the stars and emit little or no radiation.

2. The Age of our Solar System • Astronomers think that our solar system formed about 5 billion years ago. Our Milky Way Galaxy is thought to have begun formation 13.7 billion years ago and our universe is thought to have formed 13-14 billion years ago.

3. Our Solar System Formation A nebula made up of mostly hydrogen and dust containing some heavier elements like carbon, oxygen, nitrogen and iron (from a former supernova explosion) began contracting and spinning. As the cloud spun it began to flatten into a disk and to heat due to gravity pressing it smaller.

4. Our Solar System Formation Spinning caused particles to collide and to clump together. The lighter particles (ices) moved to the outside of the disk while the heavier particles moved towards the centre. As the clumps of particles grew is size their gravity also increased pulling more particles to them. These clumps became the planets.

5. Our Solar System Formation When the centre of the disk reached a temperature of 10 000 000 C, fusion began there and the sun was born. As the sun radiated light and heat energy as well as energetic particles from itself (solar wind), it pushed the remaining nebula out into space leaving the planets behind.

6. A A Summary of the Birth of our Solar System.

8. Rotations and Revolutions of the Planets The planets revolve about the sun in nearly the same flat plane (Pluto – not a planet- orbits at an angle). All planets rotate or spin like tops in the same direction except Venus and Uranus.

9. Rotations and Revolutions of the Planets Planets like Earth, Mars, Saturn and Neptune spin around a tilted axis which gives them different yearly seasons.

10. Circles and Ellipses An ellipse is an oval which has two foci (special points used to construct an ellipse). A circle is really a special ellipse in which the two foci are in the same place, the centre.

11. Planet Orbits : Ellipses with the sun on one focus The planets all orbit the sun in ellipses in which the sun is on one of the foci of the ellipse.

12. The Sun The sun contains 99.86% of the mass of our solar system. It is composed mostly of hydrogen gas which makes other heavier elements like helium and lithium in its centre by the process of atomic fusion.

13. Sun Composition The sun is made up of about 75% hydrogen, 23% helium and less than 2% oxygen, carbon, neon and iron. It’s elements are in the fourth state, the plasma state, a gas-like state in which many particles are charged causing the plasma to respond to magnetic fields. The sun’s core is 150 times as dense as water.

14. Sun Statistics The diameter of the sun is 1 392 000 km. On average, the sun is 149 600 000 km from earth. It takes 8 min 19 sec for light to reach earth from the sun. The sun’s core is at 13 600 000 C, its surface is at 5,500 C and its outer atmosphere is at 3 000 000 C.

15. Sun Structure The centre or core of the sun fuses hydrogen into heavier elements at a temperature of 13 600 000 C. The thin outer layer, the photosphere at 5500 C emits photons of light . The inner sun atmosphere layer, the chromosphere at 6 000 – 20 000 C is at times penetrated by loops called solar prominences and outward bursts called solar flares which release huge bursts of particles into space.

16. Sun Structure The outer sun atmosphere layer at 3 000 000 C is called the corona. Bursts of energetic gases into the corona spew out high energy particles into space called solar wind. Solar wind particles which would kill life on earth are deflected by the magnetic field of the earth.

17. The Northern Lights The earth’s magnetic field called the magnetosphere deflects solar wind away from the earth. Some of the solar wind particles get trapped at the north and south poles and as they slowly penetrate down to the upper atmosphere layers, these particles give off energy in the form of light which is referred to as the Northern (Southern) lights.

18. Sunspots Sunspots are cooler regions on the photosphere associated with strong magnetic activity. Eventually they usually erupt into solar prominences. The number of sunspots usually rises and falls in an 11 year cycle. High sunspot activity is associated with higher temperatures on earth. In the 1600s the sunspot activity dropped dramatically for a few decades and this produced a little ice age on earth with lower summer temperatures, colder winters and advancing glaciers.

19. The Sun Supports Life and Makes Our Weather All living things get their energy to live from their food which ultimately comes from plants. Plants store sunlight energy in their parts using the process of photosynthesis. The sun also heats the earth causing clouds, winds, rain, tornadoes, hurricanes – our weather. The sun makes life possible on earth.

20. The Sun: Our Extinguisher Formed about 4.6 billion years ago, the sun is increasing in brightness and energy level about 10% every billion years. Astronomers estimate that in 1 billion years from now, the earth will be too hot for liquid water to exist which will be the end of all life on planet earth. 5 billion years from now the sun will become a red giant expanding outward to scorch the dried-up earth.

21. The Astronomical Unit (AU) One astronomical unit is the average distance that earth is from the sun (1 AU = 150 000 000 km). Astronomical units are used to measure the large distances between planets in our solar system. Jupiter is 5.27 AUs from the sun.

22. Inner and Outer Planet Differences The inner terrestrial planets (Mercury, Venus, Earth and Mars) are rock-like with higher densities while the outer gas giant planets (Jupiter, Saturn, Neptune and Uranus) are composed of ices and gases that have much lower densities.

23. Planetary Density and Size Differences The gas giant planets are large with low densities (not tightly packed) – they almost became stars. The terrestrial planets are much smaller with much higher densities. <- Saturn

24. Mercury Mercury is the smallest planet, about 1/3 the size of earth. It has no atmosphere and its temperatures range from 400 C in the day to –183 C at night. Constant heating and freezing has produced cracks on mercury’s surface and it has many craters from meteor impacts.

25. Mercury Mercury takes about 88 days for one revolution and rotates 3 times for every 2 revolutions. Thus a Mercury ‘day’ would be about 59 Earth days and a Mercury ‘year’ would be 88 Earth days.

26. Mercury Surface Features Mercury has an iron core and a magnetic field about 1% of earth’s magnetic field. The surface of Mercury is heavily cratered and has mountains

27. Venus (In mythology the goddess of love) Venus is similar to Earth in size, mass (80% Earth’s mass) and composition but is very different in temperature and atmosphere (mostly CO2). The surface of Venus is not visible due to its heavy cloud cover. Sulphur gases from Venus mix with moisture in its atmosphere to produce sulphuric acid (battery acid) which it rains from its clouds.

28. Venus : A Hot, Waterless, High-Pressure Place The surface temperature is a fairly constant 460 C both day and night due to the CO2 atmosphere which traps and holds heat. The atmosphere and clouds press on the surface with a pressure that is 92 X Earth’s atmospheric pressure. The thick atmosphere has surface winds of low speeds but capable of carrying small stones. Higher up the winds reach speeds of 300 km/h. Venus may have had water early in its life but it has all evaporated away and been expelled into space.

29. Venus’ Rotation and Revolution Venus takes 243 Earth days to rotate once and 225 Earth days to revolve once around the sun. Thus a day on Venus is longer than one of its years. Venus rotates in the reverse direction of all the other planets so the sun would rise in the West and set in the East. Venus’ axis is not tilted so it would show no seasons.

30. Surface Features of Venus Venus has two raised continents : Ishtar Terra and Aphrodite Terra (There is no water between these on Venus). A large mountain, Maxwell Montes, is found on Ishtar Terra. Shown below is Mt. Everest, Maxwell Montes and Olympus Mons (Mars) the largest mountain in our Solar System.

31. Surface Features of Venus There are about 167 volcanoes (many more than Earth) and about 1000 impact craters (one 280 km across) from meteors etc. (many more than can be seen on Earth). Aphrodite Terra Continent has many fractures and faults.

32. Venus is Very Dim at its Surface Due to its thick covering of clouds, Venus is very dim at its surface. Lightning (static electricity discharges) also happens as clouds rub past each other, building up charges and then releasing the energy in sparks of lightning.

33. Venus has no Magnetic Field Since Venus has no magnetic field, it is unable to shield itself from the solar wind which continually strips away parts of Venus’ atmosphere, especially hydrogen, oxygen and helium atoms.

34. Planet Earth Planet Earth is the only planet which has solid, liquid and gaseous water. Three-quarters of earth’s surface is covered with liquid water. Liquid water keeps Earth from warming too greatly or cooling too greatly as does gaseous water, especially in the form of clouds.

35. Earth : Full of Living Organisms Planet Earth is the only planet in the universe that we know has life. Astronomers have yet to find a planet on which other living things have been found.

36. Earth’s Atmosphere : Shields from Harmful Radiation Earth’s atmosphere is 78% nitrogen, 21% oxygen and 1% argon. Nitrogen and oxygen are very important elements for living things. The Earth’s magnetic field shields the Earth from harmful solar wind particles and a lower ozone layer blocks harmful light radiation from the sun.

37. Earth’s Atmosphere : Warms Earth and Burns Meteors Clouds and gases like CO2 and methane act like blankets to help to hold in heat and keep Earth warmer. When meteors hit Earth’s outer atmosphere, they heat up due to friction and usually burn up before hitting the Earth’s surface.

38. Occasional Meteor (Asteroid) Impacts on Earth To make it through Earth’s atmosphere without burning up, a meteor/asteroid must be very large. The number of craters from these are few on earth since most fall into the oceans and when they fall on land, plant growth tends to obscure them.

39. Occasional Meteor (Asteroid) Impacts on Earth Past meteor/asteroid impacts on Earth are thought to have put enough dust into the atmosphere to produce a global winter for years and cause mass extinctions (the dinosaurs).

40. The Earth has Plate Tectonic Processes The Earth is made up of about 12 massive plates that move on top of a hot, fluid, tar-like layer below. The shifting of these plates causes earthquakes, volcanoes and builds mountain ranges.

41. The Earth has Plate Tectonic Processes Today’s separated continents were in the past joined together in one land mass (called Pangaea). Similar dinosaur fossils are found in most continents because they were millions of years ago joined together when Earth had a warmer climate. Fossils of tropical organisms are found in Antarctica, indicating a different climate in the past and a different place than the South Pole.

42. Mars (In mythology the god of war) Mars has a reddish colour due to the iron oxide (Fe2O3) found in its rocks. Mars is about half the size of Earth and has a very thin atmosphere of CO2. Winds on Mars can reach speeds of 900 km/h and dust storms can extend over the whole planet for weeks at a time. Mars’ gravity force is only 38% of the Earth’s gravity force.

43. Mars’ Revolution Rotation and Tilt Mars takes 687 Earth days to revolve once (a Mars year) around the sun. Mars rotates once every 24 h and 40 min (A Mars day). Mars is tilted on its axis similar to earth which creates seasons on Mars.

44. Mars’ Revolution Rotation and Tilt Surface temperatures range from -140 C at the poles in Winter to 27 C in the hottest regions at the equator in Summer. In the subtropics, day temperatures range around -5 C while night temperatures range around -85 C.

45. The Martian Atmosphere Mars’ atmosphere (11 km deep) is 95% CO2 , 3 % nitrogen and 1.6 % argon. The atmosphere is very thin so that its pressure at Mars’ surface is only .03 kpa – 2 kpa as compared to Earth’s 101.3 kpa (Mars has about 1% of earth’s atmospheric pressure). Mars has no magnetic field now but did have one millions of years ago. Solar winds continually sweep away upper parts of Mars’ atmosphere.

46. Mars’ Surface Because of Mars’ distance from the sun it is only 43% as bright on its surface compared to Earth. Martian polar ice caps are made up of solid water with a covering of solid CO2 (dry ice). Liquid water does not appear to exist on Mars.

47. Mars’ Moons Mars has two moons, Phobos (fear) and Deimos (panic). Phobos rises in the west, takes 5.5 h to set in the east and in 5.5 h rises again. Deimos takes 2.7 days to set after it has risen and another 2.7 days to rise again. Both Phobos and Deimos seem to be asteroids that were captured by Mars’ gravity. Phobos Deimos

48. Phobos and Deimos are Small Moons

49. Mars’ Surface : Volcanoes In number, Martian volcanoes are similar to Earth but they are much greater in size. Olympus Mons, the largest volcano in our Solar System, rises to 24 km in height and has a diameter of 550 km. Around its edges, there is a 6 km tall scarp (cliff drop).

50. Mars’ Surface : Impact Craters Mars is covered with many impact craters, much more than Earth has. Mars’ thin atmosphere is unable to burn up incoming meteors and asteroids. Some craters are hundreds of km across (400 km +).