UNIVERSITY OF TORONTO Faculty of Arts and Science February 28 2001 GLG130HS Exploring the Solar System Term Test No Examination aids allowed Name Student #

Read all questions carefully. Each multiple choice question is worth one point: choose the best answer. The point value of the other questions are given in square [ ] brackets. There are eight (8) pages to the exam. If you have not already done so, write your name and student number onto the exam now. Part 1
Fill in the correct word that can be associated with the statements given below. Use the list of answers provided. You may use the same answer more than once.

ANSWER LIST Hydrogen, Moon, Sun, Earth, Jupiter, Saturn, Uranus, Neptune, basalt, anorthosite, crater, chondrite, Asteroid belt, stony meteorite, iron meteorite, stony-iron meteorite

Chondrite a type of meteorite characterized by small spheres of silicate
Asteroid Belt the Kirkwood gaps are found here
Hydrogen is the most abundant element in the sun
Anorthosite is the dominant rock type on the lunar highlands
Basalt is found both on the ocean floor of Earth and on the Moon
Stony meteorite the most abundant type of meteorite (find or fall)
Asteroid Belt meteorites are believed to originate here
Sun Is the largest and most massive body in the solar system

Part 2: Multiple Choice

1.

The principal source of the energy emitted by the Sun is

(a)

decay of radioactive substances

(b)

chemical combustion

(c)

gravitational contraction

(d)

nuclear fusion of hydrogen to form helium

2.

The temperature of the Sun's core is about

(a)

1,000,000K

(b)

13,000,000K

(c)

20,000K

(d)

5,777K

3.

The second law of thermodynamics states that

(a)

Energy is conserved

(b)

heat flows from low temperature to high temperature

(c)

the entropy in a closed system can only increase

(d)

none of the above

 

 

4.

Which planetary bodies cool faster?

(a)

Those with higher surface area to volume ratios

(b)

Those with lower surface area to volume ratios

(c)

Those with higher surface albedos

(d)

None of the above

5.

which one of the following is an asteroid?

(a)

Europa

(b)

Triton

(c)

Vesta

(d)

Mercury

6.

Maria are:

(a)

Lunar Mountains

(b)

Lunar highlands

(c)

Flat lunar basaltic flows

(d)

Regions near the lunar poles

(e)

None of the above

7.

You can find the RELATIVE ages of the lunar maria and highlands by

(a)

Crater morphology

(b)

Crater density

(c)

Crater ring size

(d)

Crater size and shape

(e)

Crater rim degradation

Part 3: Short Answer Questions

1.

Name the four fundamental forces [4]

Strong Nuclear, Electromagnetic, Weak Nuclear, and Gravity
 
 

2.

Describe the structure of an atom. Explain the difference between different elements (e.g. Hydrogen, Helium, etc.) and between isotopes of the same element. [5]

An atom consists of a nucleus containing one or more protons, and possibly neutrons, surronded by a number of electrons equal to the number of protons in the nucleus. Atoms containing different numbers of protons form different elements (one proton=hydrogen, two protons=helium, and so forth) while atoms with the same number of protons but different numbers of neutrons form isotopes.
 
 

3.

Matter is believed to be made in two general circumstances. Describe those conditions and their location in both space and time, and what type of matter is made under each of the two circumstances. Provide evidence supporting your answers [6]

Light elements (hydrogen, deuterium, helium, lithium) are believed to have been formed primarily during the Big Bang, a few minutes after the universe formed, and throughout space. Both the density and temperature of the matter were much higher than those currently found in the bulk of the universe. The fact that helium abundances are roughly the same in most stars in our galaxy and, as far as astronomers can tell in stars of very different ages, is consistent with this early origin for helium. Most of the heavier elements (e.g., carbon, nitrogen, oxygen, iron) are believed to have formed in the interiors of massives stars, or in white dwarfs that are accreting matter; in both places, the density and temperature is very high. The heavy elements are subsequently ejected into interstellar space when these stars explode. In fact, the abundances of iron, oxygen, and similar elements is seen to be higher in more recently formed stars in our galaxy, and in stars closer to the center of the galaxy; both observations are consistent with the production of these elements in supernova.

4.

How old is the solar system? Give evidence for your answer. [4]

The solar system is 4.56 billion years old, as determined by radioisotope dating of meteorites.
 
 

5.

Planets are believed to form in protoplanetary disks. Explain the evidence available in our solar system. Is there any direct evidence for the existence of protoplanetary disks? [6]

The planets in our solar system all orbit the sun in prograde, low eccenticity orbits in roughly the same plane. All three properties are consistent with formation in a disk. Futhermore, the compositions of the terrestrial planets (more refractory material in the inner planets, more volatiles in the outer planets) are also consistent with formation in a disk. Hubble Space Telescope images of protostars in star formation regions such as the Orion Nebula do show disks around many young stars.
 
 

6.

Describe the orbit of an average asteroid [3]

The orbit of a typical asteroid is prograde, has a semimajor axis in the range 2-3.5AU, an eccentricity of about 0.1, and an inclination of about 0.1 radians.

7.

What are the Kirkwood gaps, where are they, and how do they form? [4]

Kirkwood gaps are found in the distribution of asteroids with semimajor axis (or orbital period). They are found in the main asteroid belt between Mars and Jupiter, at locations where the orbital period of an asteroid would be a fraction (such as 1/3, or 4/7) of the orbital period of Jupiter. They are formed as a result of the resonant gravitational interaction between material placed at these locations and Jupiter; the orbital perturbations forced by Jupiter produce chaotic changes in the orbit of the asteroid. In particular, the orbital eccentricity of the asteroid increases with time, eventually leading to a collision between the asteroid and the sun, or between the asteroid and a planet.

8.

Describe the evidence that suggests that the Moon formed in a giant impact, as opposed to co-accreting with the Earth [4]

If the Moon co-accreted with the Earth, we would expect it to have a high iron content, in the form of an iron core. On the other hand, if the Moon formed as the result of a giant impact, the iron core of the impactor would have merged with the core of the Earth, while the debris launched into orbit by the impact would be a mixture of the mantle material from the impactor and the Earth. Thus, the most telling piece of evidence that the Moon formed from an impact is its lack of an iron core. Second, the impact scenario predicts that the Moon should be composed of material similar to that of the Earth's mantle, except that it should be depleted of volatiles. The last point follows from the fact that the ejecta should be heated to high temperatures.
 
 

9.

Compare and contrast Mercury and the Moon; density, size, cooling history, etc. [6]

Mercury is substantially larger than the Moon. Mercury also has a much higher bulk density than the Moon; this suggests the Mercury, unlike the Moon, has a large iron core. Mercury also has a substantial magnetic field, suggesting that the core may be convecting; Mercury is not yet completely cooled. In contrast the Moon has no global magnetic field; it cooled more rapidly than did Mercury, consistent with its larger area/mass ratio. The large scale lobate scarps found on Mercury suggest that the planet shrank considerably in the past, unlike the Moon. However, both bodies have heavily cratered, and therefore old, surfaces; in this sense both are geologically ``dead''.
 
 

2001-04-12