NATS 1525 Lecture 7: Tutorial_II_key
23 Jan 2019
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The History of Extraterrestrial Life Debate
In-Class Tutorial II
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.
In this tutorial, we will not discuss our modern view of the solar system but will only
consider our modern understanding of the conditions of the planets 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. Take a look at
the table in the next page. You will notice that some of the values are missing. In
particular, the average distances of the solar system bodies are not given.
Use the following formula, to ll in the values for the distances:
a = 0:4 + 0:3 2n n = 1; 0; 1; 2; :::
(1)
To make sure that you are putting in the right values, use google to double check
the distances (but do not be tempted to copy down the values o google as we need
the values produced by this law for a comparison later). While you are on it,
complete the 2nd column of the table in the next page by writing the predicted value
on the left hand side, and the actual distance value on the right hand side (for the
case of the moons of planets, take them to have the same distance as the planet).
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 (10 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 rst object discovered in
this location was Ceres.
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2. For which planet, do you see big variations between the distance predicted
by the law and the actual distance? (3 marks)
Neptune
3. 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 classi ed as a
star) was a planet. Following the prediction of Titius-Bode law for the exis-
tence of a planet between Mars and Jupiter, a new planet was discovered in
the predicted location, the dwarf planet Ceres. Google Ceres and dig out
some basic properties of it (mass, radius, distance and surface temperature).
Why is it called a dwarf planet (hint: nd out how we de ne dwarf planets)? (14
marks, de nition 10 marks, and at least 4 properties, each 1 mark))
Mass = 0.00015 M&, Radius = 473 km, Temperature= 168K and distance=2.77AU
Ceres is a dwarf planet. A planet is called a dwarf planet if it is not the domi-nant
gravitational body in the orbit and has not swept out its orbit clean.
As a note aside, the argument for the existence of a planet between Mars
and Jupiter was more of a religious one rather than a scienti c one (The
beauty and elegance of the placement of the planets must not break).
Finally, note that Titius-Bode law is not considered a scienti c law anymore
even though people are still trying to nd a rational behind it and investigate
whether it works for other planetary systems or not.
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Document Summary
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. In this tutorial, we will not discuss our modern view of the solar system but will only consider our modern understanding of the conditions of the planets 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. Take a look at the table in the next page. You will notice that some of the values are missing. In particular, the average distances of the solar system bodies are not given. Use the following formula, to ll in the values for the distances: a = 0:4 + 0:3 2n n = 1; 0; 1; 2; ::: (1)
