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The History of Extraterrestrial Life Debate In-Class Tutorial II Group Member Names and Student IDs Name: ........................................... ID: ........................................... Name: ........................................... ID: ........................................... Name: ........................................... ID: ........................................... Name: ........................................... ID: ........................................... Name: ........................................... ID: ........................................... 1 Getting to know the Solar System As discussed during the lecture, for many centuries, it was assumed that the Earth is at the centre of the Universe and the Sun along with other planets orbit it in circular orbits. the purpose of this tutorial is to help you get familiarized with some general properties of the solar system. It is interesting to keep this information in the back of your mind when we speak of people’s thoughts on the existence of life elsewhere in the solar system. In order to complete this tutorial, you will need to learn about a particular unit of distance used when talking about distances between the sun and the planets. This unit of distance is known as the Astronomical Unit (AU) and is equal to the average distance between the Earth and the Sun, roughly equal to 150 million kilometresnstead of using annoyingly large numbers, expressing the values in AU allows us to work with small numbers. For instance, we say that Venus is located at 0.7 AU (70% of the average distance between the Earth and the Sun) instead of 108,208,000 km and Jupiter is at 5.2 AU (5.2 times the average distance between Earth and the Sun) instead of 778,479,000. Now take a look at the table given in this tutorial. You will notice that some of the values are missing. In particular, the 1

average distances of some of the bodies in the solar system are not given. Use the following formula, to fill in the values for the distances: a = 0 . 4 + 0 . 3 ⇥ 2 n n = -1 , 0 , 1 , 2 , ... (1) In the above equation, each value of the “n” provides the distance of a planet from the Sun, with distances getting larger as n takes up larger values. After filling in the predicted values, try googling the actual distances between Sun and the bodies and complete the column right beside the predicted values (actual values). For the case of the moons of planets, take them to have the same distance as their parent planet. After completing the table, answer the following questions based on the information in the table. 1. Is there a distance at which the law predicts the existence of a planet for which there is no planet listed in the table? Describe (6 marks). Yes! n=3 corresponds to a distance of 2.8 AU where we see no planets listed. This is the location of the asteroid belt. The first object discovered in this location was Ceres. 2. Google the distance of Ceres, the first dwarf planet discovered. Can you now explain the significance of the value of the number in the previous question? Hint: look up the average distance of the Asteroid Belt, a band of rocks of a variety of sizes between Mars and Jupiter. (6 marks) Cere is located at 2.77 AU. The value obtained for n=3 refers to the location of Ceres or in general to the location of the asteroid belt. 3. For which planet, do you see big variations between the distance predicted by the law and the actual distance? (5 marks) Neptune 4. So, by now, you should have noticed that the law works pretty well for planets all the way to Saturn and Uranus. This law was known as the Titius-Bode law, named after Johann Titius and Johann Bode (we will disucss Bode’s position on the existence of extraterrestrial life later in this course). In fact, this law motivated the search for a planet orbiting the Sun between Mars and Jupiter. It also suggested that Uranus (which was sometimes incorrectly classified as a 2

Table 1: The Solar System Planet Average Dist. Mass Radius Surface No. of Rotational Orbital from the Sun (AU) ( ⇥ M & ) ( ⇥ R & ) Temp. ◦ C Moons Period Period Water predicted actual Mercury 0.4 0.38 0.055 0.3829 430 0 58.646 d. 87.96 days Yes Venus 0.7 0.72 0.815 0.9499 464 0 -243.025 d. 224.701 days No Earth 1 1 1 1 15 1 23h&56m 365.25 days Yes Moon 1 0.012 0.273 53 N/A 27.32 days 27.32 days Yes Mars 1.6 1.52 0.107 0.533 -63 2 24h&37mins 668.6 days Yes Jupiter 5.2 5.2 317.8 11.2 -108 67 9h&55mins 11.86 years Yes Europa 5.2 0.008 0.245 -171 N/A 3.55 days 3.55 days Yes Saturn 10 9.56 95.1 9.45 -139 62 10h&33 mins 29.451 years Yes Titan 10 0.0225 0.4 -179.5 N/A 15.945 days 15.945 days Yes Uranus 19.6 19.2 14.5 4 -197 27 17h&14mins 84 years Yes Neptune 38.8 30.11 17.14 3.8 -201 14 16h&6mins 164.8 years Yes 4

Complete the table in the previous page by filling the missing values (each answer is worth 2 marks for a total of 30). Then answer the following questions (each question is worth 1 mark). Note: You will need to remember the answers to the questions below that appear in bold for your exam. 1. Which planet has the biggest radius? Jupiter 2. Which planet is the most massive? Jupiter 3. Which planet is the hottest planet (surprise)? Venus 4. Which planet has the longest orbital period (this means the longest year)? Neptune 5. Which planet has the longest rotational period (this means the longest day)? Venus 6. Which planet has the shortest orbital period (this means the shortest year)? Mercury 7. Which planet has the shortest rotational period (this means the shortest day)? Jupiter 8. Which planet’s day is longer than its year (imagine all the festivities the inhabitants of these planets would have at sunset!!!)? Venus 9. Which planet has the closest length of day to that of the Earth? Mars 10. Which planet is completely devoid of water? Venus 5