2. Natural Science 1 Planets in the Solar System UNIT 1 Some facts about the planets in the Solar System Average distance to the Sun (A.U.) MERCURYVENUS EARTHMARSJUPITER SATURNURANUSNEPTUNE Translation period (years) Mass (Earth = 1) Radius (Earth = 1) Average density (water = 1) Rotation period (days) Known satellites 0,390,72 1,001,525,20 9,5419,1830,06 00 1263 472713 58,6--243* 11,030,414 0,426--0,72*0,671 5,45,2 5,523,91,3 0,71,21,7 0,380,95 1,000,5311,2 9,424,103,88 0,060,82 1,000,11317,8 95,114,517,2 0,240,62 1,001,8811,86 29,4684,01164,79 Key to the chart We refer to terrestrial years. The mass of the Earth taken as a reference is 5.9736 · 10 24 kg. The radius of the Earth taken as a reference is 6,378 km. The density of water is 1 g/cm 3. The asterisk means that the rotation is clockwise. Activities Note: To see some characteristics of each planet, click on its name. Finish

3. Natural Science 1 Planets in the Solar System UNIT 1 Characteristics of Mercury It is the closest planet to the Sun. If we looked at the Sun from Mercury, it would appear two-and-a- half times as big as seen from the Earth. Its surface is similar to the Moon’s, since it is full of craters and cracks, marks made by the impacts of meteorites. As it has no atmosphere light can not be dispersed, if we were on its surface the sky would appear black at all times. This lack of atmosphere is responsible for the contrasts of temperature on Mercury. When the Sun heats it, it reaches 425  C, and in the areas of shadow it goes down to –170  C. Go back to the chart clicking with the mouse on this text.

4. Natural Science 1 Planets in the Solar System UNIT 1 Characteristics of Venus Go back to the chart clicking with the mouse on this text. It is the brightest object in the sky, after the Sun and the Moon; that is why we call it the Morning Star or the Evening Star. It is similar to our planet in size, mass, density and volume, but it has no oceans. It has lots of volcanoes, rivers of lava and mountains. It rotates on its axis very slowly, in a direction opposite to that of all the other planets, so on Venus the Sun rises in the west and sets in the east. Its dense atmosphere (CO 2 ) causes a significant greenhouse effect, which increases its surface temperature up to 480 °C; that is why there is no water in liquid form.

5. Natural Science 1 Planets in the Solar System UNIT 1 Characteristics of the Earth It is the only planet in the Solar System with the necessary conditions for the development of life: average temperatures of 15 ºC, liquid water and an atmosphere with oxygen. The atmosphere, besides making life possible, protects us from the impact of meteorites and from harmful solar radiation. It rotates on its axis every 24 hours, and it revolves around the Sun approximately every 365 days: this produces day and night and the seasons respectively. It has four layers, which provide us with the natural resources we need. Go back to the chart clicking with the mouse on this text.

6. Natural Science 1 Planets in the Solar System UNIT 1 Characteristics of Mars It is called the Red Planet owing to its colour. Its surface looks like some deserts on the Earth, and it has some spectacular geological formations, such as the Valles Marineris canyon, 4,000 km long, and the volcano Mount Olympus, 24 km high. It has a very thin atmosphere made up mainly of CO 2, which freezes alternatively on each of the poles. It is believed that in the past there was water or some other fluid on the surface of Mars. Its two satellites, Phobos and Deimos, are among the smallest in the Solar System. Go back to the chart clicking with the mouse on this text.

7. Natural Science 1 Planets in the Solar System UNIT 1 Characteristics of Jupiter Go back to the chart clicking with the mouse on this text. It is the biggest planet in the Solar System: it has more matter than all the other planets put together, and its volume is one thousand times the volume of Earth. It has many satellites, and four of them (Io, Callisto, Europa and Ganymede) were discovered by Galilei in 1610. Its thick atmosphere is complex, and it is made up of hydrogen (90%) and helium (10%). It has clouds and storms, so it shows stripes of different colours and some spots, such as the Great Red Spot. It has rings made out of a rocky material, but they are less bright than Saturn’s.

8. Natural Science 1 Planets in the Solar System UNIT 1 Characteristics of Saturn Go back to the chart clicking with the mouse on this text. Saturn is the only planet with rings visible from the Earth. Its rings are formed by particles ranging in size from microscopic to ones as big as a house. Its atmosphere is made up of 75% Hydrogen and 25% Helium. It is the only planet with a density smaller than that of water. If we could find a sea big enough to put Saturn in, Saturn would float. It has many satellites, but Titan is the biggest, with a diameter of 5,150 km.

9. Natural Science 1 Planets in the Solar System UNIT 1 Characteristics of Uranus Go back to the chart clicking with the mouse on this text. It is the third largest planet in the Solar System. Its atmosphere is made up of hydrogen, methane and other hydrocarbons. From Earth it seems to be a blue colour because the methane absorbs its red light. Its rotation is clockwise and its axis of rotation is almost parallel to the plane of its orbit. Therefore, Uranus is tilted in such a way that the equator is almost at a right angle to the trajectory of the orbit. It has rings, just like the other gas planets, but they are very faint. Its biggest satellites are Titania and Oberon, and both have a similar size (1580 and 1520 km in diameter respectively).

10. Natural Science 1 Planets in the Solar System UNIT 1 Characteristics of Neptune Go back to the chart clicking with the mouse on this text. It is an outer gas giant and it is the farthest from the Sun. Its interior is composed of molten rock, methane and liquid ammonia, and the exterior consists of hydrogen, helium, water vapour and methane, which gives it its blue colour, just like Uranus. It has the strongest winds of all the planets of the Solar System; in fact around the Great Dark Spot they reach 2,000 km/h. As is the case with the rest of the gas planets, it is surrounded by rings. It has several natural satellites, and the biggest is Triton.

11. Natural Science 1 Planets in the Solar System UNIT 1 1Answer the following questions: Activities a)Which planet is the Morning Star? b)Which planet is called the Red Planet? c)Which one has the strongest winds? d)Which has a density lower than that of water? e)Where is the Great Red Spot? f)And the volcano Mount Olympus? g)Which of them has no atmosphere? 2Place the planets in order from highest to lowest according to the following: a) Mass. b) Density. c) Size. 3Draw a diagram, including the satellites shown in the text. 4Look for information about the Valles Marineris canyon and the Mount Olympus volcano. Do both geological formations belong to the same planet? 5The Great Red Spot is a storm greater in size than the diameter of the Earth. Find out the velocity of the wind that the Great Red Spot can cause. 6Sometimes the hottest part in Uranus is at one of its poles. Why do you think this is?