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 A lesson on the role of comets in our Solar System
Instructors’ Guide appropriate for ages 12 and up
keywords: comets, Kuiper Belt, minor planets,
Oort Cloud, orbit, Solar System, water
A product of
Inspi ring S cience Educatio n
created by
Pamela L. Gay
CosmoQuest.org/EducatorsZone
co smo ques t.org
DiggingIntoComets
DiggingIntoComets
A lesson on the role of comets in the Solar System
This lesson was written by
Pamela L. Gay
and was created for
Inspiring Science Education
January 2015
produced in collaboration with
CosmoQuest (SIUE) and Galileo Teacher Training Program (NUCLIO)
Creative Commons Attribution-NonCommercial (CC BY-NC) 2014
you may distribute, remix, and build upon this work non-commercially, but must retain &
provide credit to the original authors, and license derivative works on the same terms.
Funding for this project was provided by the European Commission’s Framework 7.
Table of Contents
OVERVIEW FOR EDUCATORS ........................................................................................................................... 1 ENGAGEMENT: BUILDING A COMET .............................................................................................................. 3 EXPLORE: HOW ARE COMETS DISCOVERED (PART 1) ............................................................................ 6 EXPLAIN: COMET SURVIVAL ............................................................................................................................ 7 EXPLORE: HOW ARE COMETS DISCOVERED (PART 2) ............ ERROR! BOOKMARK NOT DEFINED. ELABORATE: WHERE DO COMETS ORIGINATE .......................................................................................... 1 EVALUATE: ARE ALL COMETS COMING FROM THE SAME PLACE? ...................................................... 1 ENGAGEMENT: BUILDING A COMET .............................................. ERROR! BOOKMARK NOT DEFINED. Instructors’ Guide
Overview for Educators
Objective
The solar system is littered with Ice. The bulk of this material orbits quietly in the outer Solar
System, but sometimes, something disturbs the ice and it comes plunging in toward the Sun. In
this Hangout, we will discuss comets, how we explore them, and how they brought water to
worlds like Earth.
Grade Level
appropriate for ages 12 and up (US 6th grade & higher)
Time Required
Minimum: 120 minutes.
Keywords
comets, Kuiper Belt, minor planets, Oort Cloud, orbit, solar system, water
Next Generation Science Standards (Adaptable for 1, 5, MS, HS):
• ESS1.B: Earth and the Solar System
• ESS1-2: Developing and Using Models
• ESS1-3: Analyze & interpret data to determine scale properties of objects in
the Solar System
• SEP 2: Developing & Using Models
• CCC 7: Stability & Change
Big Science Questions
• All material in the Universe is made of very small particles.
• The composition of the Earth and its atmosphere and the processes occurring within them
shape the Earth’s surface and its climate.
Aspects of Inquiry Cycle
DiggingIntoComets: The role of comets in the Solar System
1
Sequence of activities (minimum 2 class periods or 1 lab block)
Engage:
Build a comet
Explore:
How are comets discovered with photometry
Explain:
How do comets last so long by looking at their orbits over time.
Elaborate:
Where do comets come from
Evaluate:
Are all comets coming from the same place?
Materials needed
Supplies to make a soft ball-sized comet
• Rubber Mallet (preferable) or hammer
• Window cleaner containing ammonia
• 2 heavy-duty garbage bags
• Large bowl or tub
• Cooler or ice chest for storage
• Large plastic serving spoon
• Each group or student needs
• Oven mitts
• Gallon-sized bag with secure zip top
• Water (~1/3-1/2 cup per student)
• Dry ice (3/4 cup)
• Dirt and/or sand (~3/4–1 cup)
• Pebbles or small rocks
• Dark corn syrup or cola (~1 Tbl)
• Charcoal briquettes (1/2 brick)
Hardware and software
• Salsa-J (http://bit.ly/SalsaJ)
• Celestia (http://bit.ly/Celestia-en)
Pre-Requisite Knowledge
• Planets and other objects move on elliptical orbits around the Sun
• Phases of matter include solid, liquid, gas
• The heat/brightness of the Sun and other heat sources decreases with distance
Useful Knowledge
• Familiarity with Celestia
DiggingIntoComets: The role of comets in the Solar System
2
Instructors’ Guide
Engagement: Building a Comet
Time required: 25 minutes as demo (optional: 40 minutes as a hands-on-activity)
Resources and references: This activity is based on the Dark Skies, Bright Kids activity
“Comets – A Physical Model,” which can be found at http://bit.ly/DSBKcomets
Context:
Begin with a discussion that allows you to judge the knowledge and misinformation the students
have about comets. Learning Goal: Understand what happens to comets on approaching the Sun.
Prior to Class:
Arrange all of the ingredients to build a comet on a large surface where students will not be
working and where the comet will be clearly visible. Cover the surface with one garbage bag and
then line the bowl with the other garbage bag.
Discussion Activity and Questions:
Begin by building a comet. As your first step, break apart the dry ice with the mallet as needed to
create many small pieces. Explain to the students that comets are largely made of frozen carbon
dioxide (dry ice) and water. Mix these substances, and point out both of these substances are on
Earth; we exhale carbon dioxide which makes up 0.04% of our atmosphere, and water is one of
the primary constituents of our body and covers the majority of the surface of the planet. Next,
talk about how comets contain; silicates like the dirt and rocks found on earth, ammonia like can
be found at the grocery store, and complex organic materials such as those found in corn syrup or
cola. Mix all of these ingredients together thoroughly.
• Ask students to describe what they see with words and to make a sketch.
They should note that it is a dirty snowball. Have them estimate how much of the
surface is shiny versus dirty. They should also note that it is giving off a gas they
can see. Use this to point out that ice can melt to liquid or sublimate to gas.
•
Ask students what they observe happening when the dry ice is in the warm room versus
in the cold cooler the ice came in.
They should note that the ice melts/sublimates when it is warm. Use this to explain
that in the early solar system, any ice formed inside of the asteroid belt was
melted and anything further away was able to survive.
Vocabulary Discussion
Go over the vocabulary and the diagram on the next page. Discuss:
• What part of the comet did you make above?
The nuclei
•
What part of the comet is the gas most like?
The coma
•
When will a comet reflect the most light?
When it is close to the sun because it will be bigger / have more surface to reflect
the light, and the sunlight is brighter on the comet.
DiggingIntoComets: The role of comets in the Solar System
3
Vocabulary:
• Coma – Nebulous envelope forming the surrounding the nucleus of the comet.
• Comet – A celestial object in orbit around the Sun with a nucleus of ice and dust, which
forms a tail of gas, and dust pointing away from the Sun on its approach.
• Meteor Shower – A number of meteors that radiate from a specific point in the sky on a
given date yearly. Showers occur when Earth passes through comet debris.
• Nuclei – The solid core of the comet. Typically this is only a few kilometers or less in
size. A dormant / inactive comet has no other parts.
• Orbit – The motion of celestial objects around each other when they are bound by
gravity.
• Phases of Matter – The states in which matter can exist - a solid, liquid, gas or plasma.
• Sublimation – Change in the state of matter directly from solid to gas without passing
through the liquid phase.
• Tail – Debris from the head of a comet that points away from the Sun. The tail has two
components; an ion tail of charged particles that points straight away from the sun, and a
dust tail that gets left behind by the comet’s motion.
DiggingIntoComets: The role of comets in the Solar System
4
Formative assessment question
The correct answer is underlined and in italics.
1. What would happen to a comet if it was put in an orbit like Mercury's, that is nearly
circular and keeps the comet near the Sun?
a. It would go through periodic outbursts of activity as new gas was exposed to the
sunlight.
b. The Sun's gravity would tear it apart very quickly, and the chunks would spiral
into the sun.
c. It would turn into a planet covered in water.
d. It would form a tail and coma that would initially grow quite large, and would
then shrink as the comet's mass decreases until the comet falls apart.
Evaluation questions
Note: These are PISA-style questions designed to judge the level of comprehension. All answers
are correct, but the answer selected reflects the understanding. The answers are consistently
sorted from low-performer to high-performer.
1. What happens to a comet as it approaches the Sun?
a. The nucleus will give off gas that the Sun reflects off of, making the comet more
easily visible.
b. The gas around the nucleus expands to ~10,000 times the size of the nucleus and a
tail forms.
c. The nucleus' mass is reduced as it sublimates into light-reflecting gas that
surrounds the comet and is pushed by sunlight into a tail.
2. It has so far proven impossible to see objects in the very distant Oort cloud with a
telescope on Earth. Comets are said to come from the Oort cloud. Active comets have
tails that are easily seen and very large. Why can't Oort cloud objects be seen?
a. Objects in the Oort cloud have no coma or tail.
b. Objects in the Oort cloud are inactive, and the nuclei alone are only about 10km
diameter across, which is too small to see from Earth.
c. The Oort Cloud doesn't get enough light to cause sublimation, and to the comet
nuclei alone has too small a reflective surface.
DiggingIntoComets: The role of comets in the Solar System
5
Instructors’ Guide
Explore: How are comets discovered (part 1)
Time required: 25 minutes
Resources and references: You can find a Salsa-J instruction manual at http://bit.ly/SalsaJinstruct
Context:
Comets are discovered via images of the same area of the sky that are taken several days apart.
In this activity, students will look for a comet in an image set.
Activity:
Break students into pairs and at computers. One student will be the pilot (the person who uses the
keyboard and mouse) and the other will be the navigator (instructing the navigator what to do).
Use a timer such as that found on a phone to have them swap roles every 4 minutes.
1. Have students open a provided set of images in Salsa-J
2. Students should convert the opened images into a stack using
Image > Stack > Images to Stack
3. Once the stack is created, it can be animated using
Image > Stack > Start Animation
4. Students should then look for a moving object in the image. Once it is found, students
should make a table of date/time of the image and the comet’s position (X,Y), and then
plot their points.
5. Once the moving object has been found, students should also discuss anything else they
notice in the images.
Discuss:
1. What causes the comet to move through the images?
Its orbit
2. What factors might affect the way (including rate) the comet moves through the images?
- changing alignment between the Earth and the comet
- the comet changing speed as it approaches the Sun
Related Activities:
•
•
Finding Asteroids in Astrometrica by Faulkes Telescope Project
A lesson using Astrometrica http://bit.ly/1DxBwEv
Comets and Coronal Mass Ejections by Texas Instruments
A math intensive lesson at http://bit.ly/1BEqMj9
DiggingIntoComets: The role of comets in the Solar System
6
Instructors’ Guide
Explain: Comet Survival
Time required: 30 minutes
Learning Goal:
Students should understand that comets spend most of their time beyond the asteroids.
Resources and references:
You can find Celestia instructions at http://bit.ly/Celestia-instruct. You can get the “Catalog of
Comets” data file from http://bit.ly/Celestia-Comets.
Note to Instructors:
Before class, you should download the Catalogue of Comets. It will come as a zip file. Unzip this
file and copy the resulting DIRL_comets_v#.##.ssc file to into the extras folder in your
application folder (you may have to create this folder). NOTE: There are two parts to the student
handout packet for this section: hypothesis building and the activity.
Activity Context:
Explain to students that comets like Halley's comet have been observed for centuries, even
though they sublimate off material everytime they get near the Sun. Ask student's to consider
what must be true about how long comets are near the Sun in order for this to be true. Allow the
students to talk amongst them selves while they develop their own written hypothesis. They
should also discuss how to test their hypothesis.
Additional Historic Context:
•
"Halley's Comet was spotted by ancient greeks," by Mike Wall, space.com
•
"How Halley's Comet sightings changed history over the past 2500 years," by Alasdair
Wilkins, io9.com
Activity:
Break students into pairs at computers. One student will be the pilot (the person who uses the
keyboard and mouse) and the other will be the navigator (instructing the navigator what to do).
Use a timer such as that found on a phone to have them swap roles every 4 minutes.
1. Have students pick a periodic and non-periodic comet (preferred) or two periodic comets.
Groups should try not to select the same comets. Once the comets are selected use the
Internet to look up the periodic comet’s next perihelion date, and the non-periodic
comet’s last perihelion.
2. Create a spreadsheet that has the following columns: date, day, distance
3. For each comet do the following:
a. Look down on the inner solar
system by going to:
Location è Go To Object and
setting it up as shown in Figure 1
Figure 1
b. Set the time to the time of the last
perihelion by going to:
Time è Set Time (You should now see the comet in your field of view).
DiggingIntoComets: The role of comets in the Solar System
7
c. Compare the orbit of the comet with that of the planets. Look both at its shape and
at its orientation (angle/tilt). To change your viewpoint, use the Pitch, Yaw, and
Roll options under the Direction menu.
d. Watch the comet move through the solar system from the perspective of the
surface of the Sun. To do this, change the Distance in the “Go to Object” window
to 0.0046 au.
e. To see the distance to the comet in the upper left hand corner, click
Location è Select, and search on your comet. Press return to select it. Your view
may not change. That’s ok.
f. Advance time until the comet’s distance has increased by roughly 1AU. Write
down this date and distance in the chart. Repeat this until the comet is at least 10
AU away
4. The date the comet is closest to the Sun is "Day 1." Subtract this date from each
subsequent date to get the number of days since the comet was closest to the Sun, and put
this in the day column.
5. Make one plot showing distance (Y) from the Sun versus days (x) for both comets.
An example table and plot is shown below.
EXAMPLE Discussion Context:
Students should compare their comets and draw conclusions about general cometary motion by
creating a combined graph.
Combining Data:
On a central computer, have each student copy in their comet's data. The first column of the table
is for the Days, and each subsequent column should be labled with the name of a different comet
and should contain the distance of the comet. This table will have a lot of blank cells. That is ok.
Once all the data is entered, highligh all the columns and make a plot of day versus distance
showing all of the comets.
Needed Concept:
Recall from math: The slope of the line is the change in X over the change in Y.
DiggingIntoComets: The role of comets in the Solar System
8
Discuss:
• When did the students see the comet moving fastest?
in the beginning, when still near the Sun
•
Where is the slope of the line always the steepest? This is where the comet is moving the
fastest.
near the Sun
•
What happens to the slope of the line as the comet gets farther from the Sun?
•
A typical comet orbit is tens of years. Where must the comet spent most of this time?
it flattens out
beyond 10AU, far from the Sun
Comets:
• A list of short-period / periodic comets can be found here http://bit.ly/shortPcomets
• A list of period-period / non-periodic comets can be found here http://bit.ly/longPcomets
• Comets included as of DIRL_comets_v3_02.ssc
o
o
Non-periodic comets:
§ C/1965 S1 (Ikeya-Seki)
§ C/1995 O1 (Hale-Bopp)
§ C/1996 B2 (Hyakutake)
§ C/2004 Q2 (Machholz)
Periodic Comets: listed below
Name
2P/Encke
4P/Faye
6P/d'Arrest
7P/Pons-Winnecke
8P/Tuttle
9P/Tempel 1
10P/Tempel 2
11P/Tempel-Swift-LINEAR
12P/Pons-Brooks
13P/Olbers
14P/Wolf
15P/Finlay
16P/Brooks 2
17P/Holmes
21P/Giacobini-Zinner
22P/Kopff
23P/Brorsen-Metcalf
24P/Schaumasse
26P/Grigg-Skjellerup
27P/Crommelin
28P/Neujmin 1
29P/Schwassmann-Wachmann 1
DiggingIntoComets: The role of comets in the Solar System
Next Perihelion
3/10/17
5/29/14
3/2/15
1/30/15
8/27/21
8/2/16
11/14/15
8/26/14
4/21/24
6/30/24
12/1/17
12/27/14
6/7/14
3/27/14
9/10/18
10/25/15
6/8/59
11/16/17
10/1/18
5/27/39
3/11/21
3/7/19
Pyears
3.3
7.55
6.54
6.37
13.6
5.52
5.38
6.37
70.85
69.5
8.74
6.75
6.14
6.88
6.62
6.45
70.52
8.24
5.31
27.4
18.17
14.65
9
Name
30P/Reinmuth 1
31P/Schwassmann-Wachmann 2
32P/Comas Sola
33P/Daniel
35P/Herschel-Rigollet
36P/Whipple
37P/Forbes
38P/Stephan-Oterma
39P/Oterma
40P/Vaisala 1
41P/Tuttle-Giacobini-Kresak
42P/Neujmin 3
43P/Wolf-Harrington
44P/Reinmuth 2
45P/Honda-Mrkos-Pajdusakova
46P/Wirtanen
47P/Ashbrook-Jackson
48P/Johnson
49P/Arend-Rigaux
50P/Arend
51P/Harrington
52P/Harrington-Abell
53P/Van Biesbroeck
54P/de Vico-Swift-NEAT
55P/Tempel-Tuttle
56P/Slaughter-Burnham
57P/duToit-Neujmin-Delporte
58P/Jackson-Neujmin
59P/Kearns-Kwee
60P/Tsuchinshan 2
61P/Shajn-Schaldach
62P/Tsuchinshan 1
63P/Wild 1
64P/Swift-Gehrels
65P/Gunn
66P/du Toit
67P/Churyumov-Gerasimenko
68P/Klemola
69P/Taylor
70P/Kojima
71P/Clark
72D/Denning-Fujikawa
73P/Schwassmann-Wachmann 3
DiggingIntoComets: The role of comets in the Solar System
Next Perihelion
8/19/17
7/6/19
10/17/14
8/22/16
2/17/92
5/31/20
5/3/18
11/10/18
7/11/23
11/15/14
4/23/17
4/8/15
8/19/16
Pyears
7.33
8.7
8.8
8.06
155
8.5
6
37.72
19.43
12/31/16
12/12/18
6/10/17
8/12/18
7/15/18
2/8/16
3/28/16
3/7/14
4/29/16
4/15/17
5/20/31
7/18/16
5/22/15
5.25
5.44
8.3
6.96
6.72
8.27
7.53
12.53
7.31
33.22
11.54
6.42
12/11/18
6.78
11/16/17
6.63
10/16/17
6.8
11/9/19
3/18/19
10/20/14
6/30/17
7/11/14
3/16/17
5.41
10.71
6.14
6.45
10.82
6.95
5.52
5.36
10
Name
74P/Smirnova-Chernykh
75D/Kohoutek
76P/West-Kohoutek-Ikemura
77P/Longmore
78P/Gehrels 2
79P/du Toit-Hartley
80P/Peters-Hartley
81P/Wild 2
82P/Gehrels 3
83D/Russell 1
84P/Giclas
85P/Boethin
86P/Wild 3
87P/Bus
88P/Howell
89P/Russell 2
90P/Gehrels 1
91P/Russell 3
92P/Sanguin
93P/Lovas 1
94P/Russell 4
96P/Machholz 1
97P/Metcalf-Brewington
98P/Takamizawa
99P/Kowal 1
100P/Hartley 1
101P/Chernykh
102P/Shoemaker 1
103P/Hartley 2
104P/Kowal 2
105P/Singer Brewster
106P/Schuster
107P/Wilson-Harrington
108P/Ciffreo
109P/Swift-Tuttle
110P/Hartley 3
112P/Urata-Niijima
113P/Spitaler
114P/Wiseman-Skiff
115P/Maury
116P/Wild 4
117P/Helin-Roman-Alu 1
118P/Shoemaker-Levy 4
DiggingIntoComets: The role of comets in the Solar System
Next Perihelion
1/26/18
7/9/14
Pyears
8.53
5/13/16
4/2/19
6.83
7.22
11/10/14
7/20/16
6/28/18
6.41
8.43
Lost
6.96
11.22
12/19/13
4/6/15
12/14/16
6/19/17
6.51
5.5
7.66
3/11/17
10/27/16
10/27/17
4/12/22
4/2/16
1/13/20
4/2/16
4/20/17
7/20/14
2/5/14
10/18/14
7/12/26
1/11/16
3/27/14
6/16/16
6.6
5.24
7.4
15.06
6.31
6.47
6.18
6.46
7.31
4.29
7.26
133.28
6.86
6.64
7.09
6.87
8.79
6.48
8.29
6.45
11
Name
119P/Parker-Hartley
120P/Mueller 1
121P/Shoemaker-Holt 2
122P/de Vico
123P/West-Hartley
124P/Mrkos
125P/Spacewatch
126P/IRAS
127P/Holt-Olmstead
128P/Shoemaker-Holt 1-A
128P/Shoemaker-Holt 1-B
129P/Shoemaker-Levy 3
130P/McNaught-Hughes
131P/Mueller 2
132P/Helin-Roman-Alu 2
133P/7968 Elst-Pizarro
134P/Kowal-Vavrova
135P/Shoemaker-Levy 8
136P/Mueller 3
137P/Shoemaker-Levy 2
138P/Shoemaker-Levy 7
139P/Vaisala-Oterma
140P/Bowell-Skiff
141P/Machholz 2-A
141P/Machholz 2-D
142P/Ge-Wang
143P/Kowal-Mrkos
144P/Kushida
145P/Shoemaker-Levy 5
146P/Shoemaker-LINEAR
147P/Kushida-Muramatsu
148P/Anderson-LINEAR
149P/Mueller 4
150P/LONEOS
151P/Helin
152P/Helin-Lawrence
153P/Ikeya-Zhang
154P/Brewington
155P/Shoemaker 3
156P/Russell-LINEAR
157P/Tritton
158P/Kowal-LINEAR
159P/LONEOS
DiggingIntoComets: The role of comets in the Solar System
Next Perihelion
4/2/14
4/9/14
3/17/16
1/10/17
2/11/14
5/21/14
5/21/14
11/1/14
5/31/16
12/10/17
8/30/16
8/31/17
6/30/16
2/27/16
7/24/16
4/16/14
6/10/16
Pyears
8.84
8.39
9.96
74.35
7.59
6.04
5.53
13.42
6.4
9.51
9.59
8.96
6.67
7.06
8.28
5.62
15.55
7.5
8.59
9.55
6.89
9.61
16.18
5.23
5.22
11.05
8.93
7.6
8.43
8.08
7.43
7.07
9.02
7.67
14.1
9.54
366.51
10.78
17.09
6.82
6.31
10.26
14.32
12
Name
160P/LINEAR
161P/Hartley-IRAS
162P/Siding Spring
163P/NEAT
164P/Christensen
Next Perihelion
Pyears
7.92
21.43
5.32
7.3
6.97
Evaluation questions (can be used for pre/post testing)
Note: These are PISA-style questions designed to judge the level of comprehension. All answers
are correct, but the answer selected reflects the understanding. The answers are consistently
sorted from low-performer to high-performer.
1. You had the opportunity to build a model of a comet. Comets are remains of the nebula
that formed our solar system. Research about their constitution, trajectories, etc is crucial
for our understanding of our own origins. Which statement best describes comets?
a. Comets can originate from different parts of the Solar System and studying their
orbits can provide clues on where they were formed.
b. While approaching the Sun comets suffer different physical transformations due
to the proximity to our star. The study of the tails that form during such approach
are important for analysing the constitution of these objects.
c. Some scientists claim that comets might be responsible for the origin of water on
planet Earth. The study of their orbits, their composition, etc might be important
to better understand the origin of life on Earth. Models built in laboratory might
greatly help us understand such possibilities.
2. Comets change in appearance as they approach the Sun. At great distances, from the
distance of Jupiter and beyond, it is extremely cold and comets are completely frozen. As
they come through the inner solar system, passing Mars and coming toward the Sun, they
sublimate gas and some of their material streams off as an ion tail. How can a comets'
evolution best be described?
a. Comets are fossils of the formation of the Solar System and carriers of important
information abou the birth of our Star and planets.
b. Comets can evolve with time and according with their interaction with the
surrounding environment. They develop a tail when they approach the Sun
constituted by a gas tail and a dust tail. They can extend to many kilometers in
space. Parts of comets can fall on Earth and be seen in the so called "shooting
stars", in other words, little rocks that eventually hit the surface of our planet.
c. Comets gas tails are formed due to ionization happening due to the interaction
with sunlight. They are carried away from the Sun by solar wind. The dust tail is
formed by small solid particles and is gently carried away from the comets due to
the pressure of sunlight.
DiggingIntoComets: The role of comets in the Solar System
13
3. By studying different comets you probably have noticed that they might come from
different distances to the Sun, with different periods, different inclination angles when
compared to the Sun-Earth system. Describe the beautiful dance of objects in the Solar
System form its birth till today.
a. Many comets coming from the Oort cloud where not originally born there but
ended up there after collisions with other objects in crowded places of the Solar
System
b. Some comets might have originated in the Kuiper Belt, the region where we can
find Pluto and many other dwarf planets. Many have the same characteristics as
the objects we call trans-Neptunians.
c. We know today that the region where we find Pluto has hundreds of other objects,
some perhaps even bigger than Pluto itself. The Oort cloud is another such region,
populated by hundreds, if not thousands of objects, remains of the nebula that
originated the Solar System. Despite strong belief of the scientific community
there is no proof of its existence. It is believed that it is located 100 times further
away than the Kuiper Belt.
4. Comets are not always bright objects and it is fundamental to know their existence and to
carefully track their orbits. Summarize their actual behavior.
a. Scientists are regularly observing the night sky in search of yet unknown objects.
Some are so small that can pass undetected.
b. Asteroids and comets can pose threats to our planet. Thus it is of the uttermost
importance to know where they are. The largest objects, in particular those with
high albedo, are already known. The challenge is to find those that are small
and/or don't reflect the sun's light efficiently. This is of course related to their size
and composition.
c. A technique that is very often used to track such objects is to observe the same
area of the sky and try to spot objects that move from one image to the other and
that are yet unknown. This works requires a lot of effort and careful analysis of
thousands of images. Students can do this as part of their schoolwork acquiring
important research skills while doing this
DiggingIntoComets: The role of comets in the Solar System
14
Instructors’ Guide
Elaborate: Where do comets originate
Time required: 10 minutes
Context:
Students should understand that comets originate in icy regions in the outer solar system.
Discuss:
1. Where do comets spend most of their time?
beyond the orbit of the asteroids (where they will stay frozen)
2. Does this prove or disprove the students’ hypothesis?
Vocabulary:
• Perihelion – The closest point to the Sun on an orbit.
• Aphelion – The furthest point from the Sun on an orbit.
• Meteor Shower – A number of meteors that radiate from a specific point in the sky on a
given date yearly. Showers occur when Earth passes through comet debris.
Figure: Halley’s Comet’s orbit (by Steven Dutch, University of Wisconsin - Green Bay).
DiggingIntoComets: The role of comets in the Solar System
1
Instructors’ Guide
Evaluate: Are all comets coming from the same place?
Time required: 10 minutes
Context:
Students should understand that comets with different kinds of orbits come from different places.
Discuss:
1. Comparing data across the classroom, do the orbits of short- and long- period comets
have different orientations?
short-period comets are more often in the plane of the solar system/
long-period comets are more randomly aligned
2. If comets are creating by something changing the orbit of an icy body, where do comets
originate
short-period comets come from in the plane of the solar system somewhere at or
beyond Neptune (this is the Kuiper Belt)
long-period comets come from a distant cloud of ice (this is the Oort Cloud)
Image from http://interstellar.jpl.nasa.gov/interstellar/probe/introduction/scale.html