NAME: Conor A Nixon - Solutions
University Of Maryland
Department Of Astronomy
ASTRONOMY 330: The Solar System
EXAM 1 October 5th 2006
12:30 – 01:45 (75 minutes)
Room CSS 2428
INSTRUCTIONS:
Read these instructions carefully before turning over.
This is a closed book exam: no notes, books or any other information materials may be
used. No calculators allowed. Use blue or black ink, write as neatly as you can. Do not
use correction fluid. Cross out any writing or calculations which you do not want to be
graded. No talking or communicating with other students during the exam. If you need to
ask a question of the invigilators raise your hand.
This exam has 3 parts, totaling 200 points (20% of final grade). Part 1 (50 pts) consists of
short answer questions. Part 2 (50 pts) consists of TRUE/FALSE statements. Part 3 (100
points) consists of longer, structured response questions. There are questions on both
sides of the page. Write all your answers on the exam paper. There is extra space at the
end if you need to continue any answer beyond the space provided.
Write your name at the top of each exam page, and any extra pages you use.
Read each question carefully twice through before you begin writing.
HONOR PLEDGE: (copy the honor pledge below and sign)
“I pledge on my honor that I have not given or received any unauthorized assistance
on this assignment/examination.”
Pledge:
Signed:
PART 1: SHORT ANSWER QUESTIONS (50 points total).
1. Re-write the following list in decreasing order of density (densest first): WATER,
JUPITER, MARS, SATURN, IRON, PLANET MERCURY, GOLD, EARTH’S
MOON.
The correct order is (with values in g/cm3 for information only – not required!)
GOLD (19), IRON (7.9), MERCURY (5.4), MARS (4.0), MOON (3.3),
JUPITER (1.3), WATER (1.0), SATURN (0.7).
[1 pt for each correct position = 8 pts]
2. Sketch the appearance of a comet in the inner solar system, labeling the three
main parts, and the direction of the solar wind.
The three main parts of the comet are the nucleus [2], coma [2] and tail [2], although the
question is somewhat imprecise about which tail. I will therefore accept any or all of the
three tails for the third part. The solar wind should be impacting the comet on the
opposite side to the ion tail, a bit less than 180 degrees for the hydrogen envelope, or at
some other angle for the dust tail which is typically curved [2 pts]. [TOTAL 8 pts].
3. In one sentence each, explain three astronomical technologies which are available
today, which were not available to Galileo and Newton.
Astronomical technologies include [4 pts each = 12 pts]:
(i)
Segmented mirror design – using small, light hexagonal pieces to
simulate a single large mirror, instead of a single monolithic mirror.
(ii)
Adaptive optics – using a tilting or deformable secondary mirror to
remove or subtract the twinkling of stars observed from the Earth,
caused by convection in the Earth’s atmosphere.
(iii)
Interferometry – using multiple telescopes placed along a baseline, to
give the same effective spatial resolution as a single large telescope
with a diameter equal to the baseline.
(iv)
Space Telescopes – attaching telescopes to spacecraft and sending
them into space, to avoid the Earth’s atmosphere altogether.
(v)
Orbiter or flyby spacecraft – sending spacecraft for an up-close look at
a planet, asteroid or comet.
(vi)
Landers and probes – send a robot to land on an astronomical body or
pass through its atmosphere or magnetosphere.
4. Briefly define each of the following scientific terms: [2 pts each = 10 pts]
(a) ALBEDO: the percentage of sunlight falling on a body that is reflected.
(b) BRECCIA: a rock which is composed of debris pieces of other rocks,
cemented back together again (breccias can therefore contain different
rock pieces of different ages). Typically from crusts of bodies which have
suffered extensive collisions.
(c) RADIOISOTOPE: an isotope of an atom that is unstable, and therefore
undergoes radioactive decay, emitting an alpha or beta particle, or a
gamma ray to become stable. (Except in the case of gamma radiation, the
radioisotope changes into a different element entirely).
(d) CHONDRULE: a round grain found inside a primitive meteorite.
(e) PARALLAX: the apparent change in position of a nearby star, planet etc
against the background of distant stars, when viewed from two different
locations (typically six months apart – two opposite sides of Earth’s orbit).
5. Name the three principal types of rocks that can be created on the Earth, and in
each case say how it is formed. [4 pts each = 12 pts]
(i) IGNEOUS – a rock that solidifies from a molten state: basalt etc.
(ii) SEDIMENTARY – a rock which is composed of the layered deposition of
sand, organic material etc, slowly accumulating over time on the Earth’s surface.
E.g. limestone, sandstone etc.
(iii) METAMORPHIC – an igneous or sedimentary rock which has been reburied below the Earth’s crust (subduction zone for example) and become
transformed by the application of heat and pressure, without being actually melted
into magma. E.g. marble is metamorphic limestone.
PART 2: TRUE/FALSE STATEMENTS (50 points total).
Be the Professor! In each case, circle the letter for correct statements, and cross out the
letter for incorrect statements. Then for all the incorrect statements, cross out the part of
the statement that is wrong.
[Grading: 2 pts for identifying each statement as correct or incorrect (15x2 = 30). Also 2
pts for identifying the incorrect part of the statement (10x2 = 20). Total 50 pts].
6. KEPLER’S LAWS
(a)
 Kepler’s First Law states that all the planets move in circular orbits around
the Sun.
(b)
(elliptical)
 Kepler’s Second Law states that an imaginary line joining the planet to the
Sun would sweep out equal areas in equal times as the planet moves round its
orbit.
(c)
 Kepler’s Third Law states that the square of the period of orbit is proportional
to the cube of the orbital inclination. (semi-major axis)
(d)
 Kepler’s discoveries were used by Nicholaus Copernicus formulate his
heliocentric model of the Solar System. (Copernicus came before Kepler!)
(e)
 Isaac Newton was later able to prove Kepler’s Laws by using his law of
universal gravitation.
7. EVOLUTION OF THE PLANETS
(secondary)
(a)
 A primary atmosphere is one that outgassed from the planet’s interior long
after accretion from the protosolar nebula had ceased.
(b)
 Cometary impacts, erosion by the solar wind, and thermal escape are all
mechanisms that can lead to loss of atmospheric mass.
(Earth is obviously active!)
(c)
 Io is the only geologically active body in the solar system at the present day.
(d)
 Biological activity on the Earth (other than humans) has had no significant
impact on its atmosphere.
(e)
(a very)
 Collisions in the solar system were important only up to about 3.8 billion years
ago but have ceased by the present day. (collisions are clearly still going on today,
e.g. the Shoemaker-Levy 9 comet crashing into Jupiter)
PART 2: CONTINUED
8. THE SUN
(a)
 The corona is the outermost part of the Sun’s atmosphere, and therefore the
coldest. (hottest)
(b)
 The Sun is currently powered by the process of nuclear fusion, whereby three
helium nuclei are joined to form a carbon nucleus. (fusion in the Sun at the
present epoch is the proton-proton chain forming helium from 4 hydrogen nuclei)
(c)
 Heat transport inside the Sun occurs first by radiation nearer the center, and
then by convection nearer to the surface.
(d)
 The Sun is about 5 billion years old, and will burn steadily for another 95
billion years.
(e)
(5)
 The solar wind is a stream of charged particles emitted from the Sun, which
was important in blowing away gas leftover from solar system formation.
PART 3: STRUCTURED ANSWER QUESTIONS (50 pts each question, 100 pts total).
9. ORBITS AND ASTEROIDS
(i) Make a schematic diagram of a solar eclipse, showing the relative positions of the
Earth, Moon and Sun. Draw rays of light from the Sun to show where they can
and cannot reach the Earth, and use this to explain the terms umbra and
penumbra.
[12 pts]
The UMBRA is the inner part of the shadow, where the Sun is totally blocked as seen
from the Earth. [5 pts]
The PENUMBRA is the surrounding part of the shadow, where the Sun is partially
blocked as seen from the Earth. [5 pts]
(ii) Make a similar sketch for a lunar eclipse. The Moon never appears completely
dark in a lunar eclipse – why? Use your sketch to explain.
[12 pts]
Even when the Moon is in the total shadow of the Earth it is never completely dark,
because the Earth has an atmosphere that bends (or refracts) light in a curved path around
the Earth and onto the Moon. [6 pts]
(This is also the reason why the Moon is redder during an eclipse, because the Earth’s
atmosphere preferentially scatters blue light and transmits red light!)
(iii) Asteroid eclipses of stars are also important. Explain what information we may
obtain, and how we obtain it.
During the eclipse of star by an asteroid, the shadow of the asteroid falls on the Earth. By
observing the star from multiple positions, the size and extent of the shadow may be
found from which we can deduce the asteroid diameter. Moreover, by careful observing
from enough locations, the shape of the asteroid may be determined as well.
[10 pts]
(In principal, we could tell if it had a moon or an atmosphere too!)
10. METEORITES
(a) Describe one famous historical meteorite fall or find, mentioning its scientific
significance. [10 pts]
There are many mentioned in class:
L’Aigle Fall – many meteorites fell on the village of L’Aigle, France in 1803. Prior
to this event, reports of rocks falling from the sky were not taken seriously, but this
fall was witnessed by so many people that it became the start of scientific interest in
meteorites.
Allende Fall – in 1969 a huge explosion over Allende, Mexico resulted in tons of
rocks falling to Earth and being recovered. The Allende Fall is the oldest dated
meteorite pieces.
Murchison Meteorite – later in 1969 another meteorite exploded over Australia
scattering pieces over a wide area. Murchison fragments turned out to be
carbonaceous chondrites that showed the first ever evidence of amino acids in extraterrestrial material.
ALH84001 - famous Antarctic meteorite found to be from Mars.
Peekskill Meteorite – 1992 fall which was video recorded by 16 different people,
enabling its orbit to be determined exactly, pointing towards the asteroid belt.
Tagish Lake Fall – fall in 2000 in Yukon territory of Canada. Yielded over 500
samples of primitive, very fragile carbonaceous meteorite.
Hoba Iron – largest (iron) meteorite piece ever found.
Barringer Meteorite – very large iron meteorite that fell 50,000 years ago and caused
the Barringer crater in Arizona.
Springwater Pallasite – large stony-iron meteorite that fell on Canada in 1931.
Los Angeles 001 – another Martian metorite.
(b) Sketch a differentiated asteroid. Add labels to show where the following types of
meteorite might originate: DIFFERENTIATED ROCK, IRON, STONY-IRON,
BRECCIA.
[20 pts]
A differentiated asteroid shows a layered interior, with iron separated out in the center,
and overlaid by a mantle of differentiated rocks. There is also a transition layer between
the two. Each layer corresponds to a different type of meteorite:
CRUST – breccia
ROCK MANTLE – differentiated stones.
TRANSITION/BOUNDARY LAYER – stony-irons.
IRON CORE – irons.
(c) Explain the use of radioactivity in dating meteorites. How can this lead to
multiple different estimates of age?
Rocks contain naturally radioactive isotopes, such as 40K 238U and 87Rb. Once the
composition of the rock becomes fixed (usually when it solidifies) then the amount of
each radioisotope it set to an initial amount. Over time, this radioactive sample decays at
a fixed rate known as the half-life – the time required for exactly half the sample to
decay. By measuring the amount of each radioisotope remaining at present day, and
having some way of determining the initial amount (usually by sister isotopes) then the
age can be determined. [10 pts]
Usually the age is determined from solid parent and daughter isotopes, which means that
the amounts cannot have changed since the rock was last molten. This lead to the
solidification age. However, if either the parent or daughter is a gas, as in the case of
potassium-argon decay, then the amounts of each substance can change when an impact
occurs and the rock is violently disturbed, but without actually becoming molten. Such is
the case when a breccia forms for example. Dating the gaseous isotopes then leads to a
gas retention age, the time since the rock was last involved in a major impact. [10 pts]