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The Nine Planets (13.14) The Inner Planets The four planets closest to the Sun are Mercury, Venus, Earth, and Mars. All four of these planets are made up of a rocky material and therefore are called the terrestrial planets. These planets are also known as the inner planets. Mercury Mercury is the closest planet to the Sun; therefore, it gets sunlight that is 10 times brighter than the Earth’s. Mercury does not have an atmosphere to help trap the heat it receives from the Sun, so it loses all of its heat at night dropping to -180 degrees Celsius (oC). Mercury’s daytime temperature is a sweltering 400 (oC). Mercury is rarely seen in our night sky because it is so close to the Sun. When we do see Mercury, it is generally at sunset and at sunrise. Venus After the Sun and the Moon, Venus is the brightest object that we can see in the sky because it is so close to our planet Earth. Also, the atmosphere on Venus is very thick and the light it receives from the Sun is reflected to us. Venus’s atmosphere is made up from mainly carbon dioxide. This gas acts like the glass of a greenhouse and keeps the surface of the planet hot enough to melt lead. Earth Life has grown on Earth because the atmosphere on this planer is perfect for beings to have changed. Earth’s atmosphere is mainly made up of nitrogen, oxygen, and water vapour. There is a small amount of ozone in our atmosphere and this is what filters some of the damaging radiation from the Sun. Water from lakes, oceans, and rivers covers approximately 70% of planet Earth. The rest of the Earth’s surface is covered by soil, which allows for the growth of vegetations and habitat for land creatures. Earth is changing every day because of several environmental factors such as volcanoes, earthquakes, and pollution. Mars Mars is one of the brightest planets in the sky and is sometimes referred to as the “RED Planet” because of the reddish tinge it casts. This reddish colour is caused by the rust-coloured soil. Mars is very dry and barren, but there is evidence that Mars was once covered with volcanoes, glaciers and flood waters. The Outer Planets The remaining 5 planets in our solar system are known as the outer planets: Jupiter, Saturn, Uranus, Neptune and Pluto. The first 4 of these planets are also known as the Gas Giants. Their atmosphere consists mainly of hydrogen and helium. These planets have soupy surfaces and gets denser as you sink to the middle. Not possible to land on. The outermost planet, Pluto, is unique among the outer planets. Jupiter Jupiter is the largest planet of all of the planets. Its diameter is 11 times larger than Earth’s diameter. Its mass is greater than the masses of all the other planets combined. Jupiter is also a very bright object in the night sky because of its size and the large amount of light reflected by its clouds. Jupiter’s most interesting features are its coloured bands and the Great Red Spot. Jupiter has approximately 16 moons, and sometimes you can see four of these moons by using binoculars. Saturn Saturn is the second-largest planet, but it is the least dense of all the planets, with a possibility of no core. Saturn’s atmosphere is cloudy and windy. Saturn’s average temperature is -180oC. Uranus Uranus’s diameter is 4 times larger than Earth. Its atmosphere is made up primarily of hydrogen, with some helium and methane. This planet has winds that blow up to 500 km/h. In our night sky, Uranus looks like an extremely faint star. Neptune From Earth, Neptune is barely visible with the use of a telescope. Neptune has bright blue and white clouds and a dark region – the Great Dark Spot – that appears to be the centre of a storm. Neptune has at least 8 moons and thin rings orbiting around it. Pluto Pluto is now classified as a dwarf planet. It is unusual because it is not a gas giant and it does not seem to be terrestrial. The motion of Pluto’s orbit suggests that Pluto may have been one of Neptune’s moons at one time. Pluto also has a moon called Charon which is about the same size as Pluto. Planetary Summary Closest to Brown crater 59 days the Sun 0.386 0 Chunks of rock none To orbit Sun 2nd from Hot enough to A 1.7 KM high 0.72 0 CO2, N2 the Sun melt lead Volcano Volcanoes, 3rd from 1 1 Soil and Water N 2, O 2 hurricanes the Sun Reddish Volcanoes, 4th from 0.5326 2 CO2, N2 the Sun coloured soil glaciers 5th from Coloured Bands, Winds, the Sun 11 63 Great Red Spot H2, He, CH4 hurricanes 6th from Surface temp. is H2, He, CH4 Windy, the Sun 10 33 About -180o cloudy 7th from Polar hood over 500 km/h the Sun 4 29 South pole H2, He, CH4 winds 8th from 3.8 13 It’s blue. H2, He, CH4 Dark spot the Sun 9th from 0.186 3 Cold and rocky none Rotates on the Sun side Questions – p. 428: 1, 3, 9 1. Why are the four planets closest to the Sun called the “terrestrial planets”? The word terrestrial refers to Earth. Mercury, Mars, and Venus have several properties in common with Earth, so together the four planets are called the terrestrial planets 3. Why is Jupiter easy to see in the night sky? Jupiter is very large, and its atmosphere reflects a lot of light from the light. 9. List the steps that were followed in discovering Neptune. How do these steps relate to the process of scientific discovery? Scientists observed that Uranus was a plant; then they discovered that its motion was not smooth. They made a hypothesis that another object was tugging on Uranus. They predicted where the other object was; then they tested their hypothesis and discovered Neptune. This process resembles scientific discovery: observing brings more questions followed by hypothesis, predicting, and testing.
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