Exploring Ice I MAIN MENU IN THE SOLAR SYSTEM C E
SCIENCE & LITERATURE 2 L
CONCEPT OVERVIEW 3 I N PRE K–GRADE 2 CONCEPTS 3
GRADE 3–GRADE 5 CONCEPTS 3 T
LESSON SUMMARY & OBJECTIVES 4 H E
STANDARDS 5 E
ESSENTIAL QUESTION 8 S
ACTIVITY QUESTION 8 H BACKGROUND 9 A
ACT OUT THE SCIENCE 16 D
MATERIALS 20 O S
DEMONSTRATION 20 W PRE K–GRADE 2 21 S GRADE 3–GRADE 5 21 MAIN ACTIVITY 22
PREPARATION 22 S TEACHING TIPS 22 WARM-UP AND PRE-ASSESSMENT 23 PROCEDURES 24 DISCUSSION AND REFLECTION 27
CURRICULUM CONNECTIONS 28 O ASSESSMENT CRITERIA 29 RESOURCES 30
PHOTO GALLERY N D I R E This lesson develops pre- C cursor understanding about how we detect the T presence of ice on the O
permanently shadowed R
craters of Mercury and Y the Moon. Exploring Ice LESSON 12 DIRECTORY MAIN MENU IN THE SOLAR SYSTEM ICE IN THE SHADOWS
SCIENCE & LITERATURE
“…I had journeyed down To where the shades were covered wholly by ice…. Through a round aperture I saw appear Some of the beautiful things that Heaven bears Where we once more came forth, and once more saw the stars.” —Dante’s Inferno Robert Pinsky translation
The discovery of ice in the forbidding shadows of impact craters on two airless inner planets is most surprising. That we have the knowledge and technology to detect—that through the round apertures of spectrometers and radar telescopes, we can even get a glimpse of places where sunbeams never strike is as amazing and as elegant as the evocative closing lines of Dante’s great 14th century poem.
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CONCEPT OVERVIEW This lesson develops precursor understanding GRADE 3–5 CONCEPTS about how we detect the presence of ice on ■ The more direct the angle of sunlight, the permanently shadowed craters of Mercury the stronger its effect. and the Moon. ■ The effect of sunlight shining on a spherical Concepts: surface, like a planet or a moon with low obliquity is strongest in the equatorial 1. Sunlight striking spherical surfaces. 2. Detecting gamma rays & neutrons. region and weakest at the poles. (Obliquity is the tilt of a body with This lesson provides concrete experiences of: respect to its plane of orbit around 1. The angle of sunlight striking a planetary the Sun). surface. ■ Cold traps exist where there is no sunlight 2. Temperature and pressure conditions in (extremely low temperature) and no a “cold trap.” atmosphere (no air pressure), in the 3. How science instruments detect ice on permanently shadowed craters near Mercury and the Moon. the poles of Mercury and the Moon.
■ We detect the likely presence of ice PRE K–2 CONCEPTS in the cold traps by using different ■ Direct sunlight is warmer than kinds of science instruments called indirect sunlight. spectrometers that measure gamma rays and energetic neutrons. ■ It is extremely cold where there is no sunlight and no atmosphere.
■ There are places on Mercury and the Moon where there is no sunlight and no atmosphere PRINT (no heat source, no air pressure)—in the permanently shadowed craters near the poles.
■ We can detect the presence of ice in shadowed craters near the poles of Mercury and the Moon.
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LESSON SUMMARY & OBJECTIVES When cosmic rays strike the surface of Objective 1: Notice that sunlight strikes an airless world they create a moving a planet at different angles. cascade of photons and particles, including A planetary object is spherical. As sunlight gamma rays and neutrons. By measuring radiates from the Sun it strikes the surface this cascade with a Gamma Ray and Neu- of a planetary object most directly at its tron Spectrometer, scientists learn a great equatorial region and least directly at its poles. deal about the composition of the world, This means it is possible that on some Solar including detecting the presence of ice System worlds there are places near the polar in otherwise hidden places: such as the region that NEVER get sunlight. permanently shadowed craters of Mercury Objective 2: Notice that ice can exist and the Moon. where there is no sunlight and no air. Infalling ice from the outer Solar System can strike places like Mercury and the Moon and stay intact for billions of years in a cold trap— where with no sunlight, the temperature is so low that there is virtually no molecular motion, and where with only a near-vacuum exosphere, there is no air pressure. Under these conditions, ice is stable.
Objective 3: Notice that we detect evi- dence of ice on Mercury and the Moon. Water ice can be cold-trapped in permanently shadowed craters near the polar regions of PRINT Mercury and the Moon. In both cases, remote sensors have detected radar-bright patches that are likely indicators of ice. Looking for ice on the Moon has led to even more exciting ways to look for ice on Mercury.
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STANDARDS BENCHMARKS: NSES: 4E The Physical Setting: Energy Transfor- Content Standard D Earth and Space mations Science: Objects in the sky GRADES K–2, PAGE 83 GRADES K–4, PAGE 134 ■ The sun warms the land, air, and water. ■ The sun provides the light and the heat 4D The Physical Setting: the Earth necessary to maintain the temperature of the Earth. GRADES 9–12, PAGE 70 ■ Life is adapted to conditions on the Earth, Content Standard D Earth and Space including the force of gravity that enables Science: Earth in the Solar System the planet to retain an adequate atmos- GRADES 5– 8, PAGE 161 phere, and an intensity of radiation from ■ The sun is the major source of energy for the sun that allows water to cycle phenomena on the Earth’s surface, such as between liquid and vapor. growth of plants, winds, ocean currents, and the water cycle. Seasons result from ■ Weather (in the short run) and climate (in the long run) involve the transfer of variations in the amount of the sun’s energy in an out of the atmosphere. Solar energy hitting the surface due to the tilt radiation heats the landmasses, oceans, of the Earth’s rotation on its axis and the and air. Transfer of heat energy at the length of the day. boundaries between the atmosphere, the landmasses, and the oceans results in lay- NCTM MATH STANDARDS ers of different temperatures and densities Geometry Standard for Grades Pre-K–2 in both the ocean and atmosphere. The Expectations: prekindergarten through action of gravitational force on regions of grade 2 all students should: different densities causes them to rise or ■ Analyze characteristics and properties of PRINT fall—and such circulation, influenced by two- and three-dimensional geometric the rotation of the Earth, produces winds shapes and develop mathematical argu- and ocean circulation. ments about geometric relationships. – recognize, name, build, draw, compare, and sort two- and three-dimensional shapes – describe attributes and parts of two- and three-dimensional shapes – investigate and predict the results of putting together and taking apart two- and three-dimensional shapes
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■ Specify locations and describe spatial rela- Geometry Standard for Grades 3–5 tionships using coordinate geometry and Expectations: In grades 3–5 all students other representational systems should:
– describe, name, and interpret relative ■ Analyze characteristics and properties of positions in space and apply ideas two- and three-dimensional geometric about relative position shapes and develop mathematical argu- – describe, name, and interpret direction ments about geometric relationships and distance in navigating space and – identify, compare, and analyze attrib- apply ideas about direction and distance; utes of two- and three-dimensional – find and name locations with simple shapes and develop vocabulary to relationships such as “near to” and in describe the attributes coordinate systems such as maps – classify two- and three-dimensional shapes according to their properties ■ Apply transformations and use symmetry to analyze mathematical situations and develop definitions of classes of shapes such as triangles and pyramids – recognize and apply slides, flips, and turns – investigate, describe, and reason about the results of subdividing, combining, – recognize and create shapes that have and transforming shapes symmetry – explore congruence and similarity ■ Use visualization, spatial reasoning, and geometric modeling to solve problems – make and test conjectures about geometric properties and relationships – create mental images of geometric and develop logical arguments to justify shapes using spatial memory and PRINT conclusions spatial visualization – recognize and represent shapes from different perspectives – relate ideas in geometry to ideas in number and measurement – recognize geometric shapes and struc- tures in the environment and specify their location
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■ Specify locations and describe spatial ■ Use visualization, spatial reasoning, and relationships using coordinate geometry geometric modeling to solve problems and other representational systems – build and draw geometric objects – describe location and movement – create and describe mental images of using common language and objects, patterns, and paths geometric vocabulary – identify and build a three-dimensional – make and use coordinate systems to object from two-dimensional repre- specify locations and to describe paths sentations of that object – find the distance between points along – identify and draw a two-dimensional horizontal and vertical lines of a coor- representation of a three-dimensional dinate system object
■ Apply transformations and use symmetry – use geometric models to solve prob- to analyze mathematical situations lems in other areas of mathematics, – predict and describe the results of such as number and measurement sliding, flipping, and turning two- – recognize geometric ideas and rela- dimensional shapes tionships and apply them to other – describe a motion or a series of disciplines and to problems that arise motions that will show that two in the classroom or in everyday life shapes are congruent – identify and describe line and rotational symmetry in two- and three- dimensional shapes and designs PRINT
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ESSENTIAL QUESTION ACTIVITY QUESTION What Does Ice in the Shadowed Craters Why Is There Ice at the Poles of Mars, of Mercury and the Moon Tell Us About Earth, Mercury, and the Moon? the Solar System? Why are polar regions colder than the rest How can ice remain stable in the shadowed of the planet? What role does the angle of craters? Where does the ice come from? sunlight play? How can ice be on a planet What can we learn by detecting and com- so close to the Sun (Mercury)? How can paring the ice on Mercury and the Moon? we detect the presence of ice on places like the Moon and Mercury?
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BACKGROUND Earth’s 23.5º Axial Tilt and Sphericity In our era the Earth tilts at an angle of about 23.5º and aligns with the North Pole pointing toward Polaris, the North Star. In its orbital path around the Sun, the tilt of the Earth remains the same: always close to 23.5º pointing toward Polaris. Generally the equatorial region of the Earth receives the most direct sunlight. The light at the poles varies within more or less grazing angles. (The angle of sunlight is only part of the story: Earth’s atmosphere also influences how solar radiation is distributed with its resulting weather and climate conditions.) The Tropic of Cancer marks the northern- most latitude (23.5º N) of direct sunlight, which occurs on the June solstice. On that day, the North Pole receives 24 hours of sunlight and the South Pole receives 24 hours of darkness. The Tropic of Capricorn marks the southern- most latitude (23.5º S) of direct sunlight, which occurs on the December solstice. On PRINT that day, the South Pole receives 24 hours of sunlight and the North Pole receives 24 hours of darkness.
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The position of the Earth in relation to the It’s not surprising that this is hard to visualize. directness of the sunlight changes a bit each Our everyday experience on the surface of day, marked by four familiar transition points: the Earth is a sensation of a flat expanse more than an expansive curvature. Only when ■ The summer solstice—summer in the north- ern hemisphere, when sunlight is most direct we get a glimpse from space or project our at the Tropic of Cancer (23.5º N latitude); knowledge of the Earth’s curvature onto a winter in the southern hemisphere model, like a globe, does our mind begin to cope with the meaning of living on a spinning, ■ The fall equinox—autumn in the northern spherical, and tilted planet. hemisphere, spring in the southern, when sunlight is most direct at the Equator Depending on the time of year, the latitudes between 23.5º N and 23.5º S receive the ■ The winter solstice—winter in the most direct sunlight. As you move north or northern hemisphere, when sunlight is south toward the poles, the sunlight is less most direct at the tropic of Capricorn direct because the Earth’s surface curves (23.5º S latitude); summer in the away from the direct sunlight. As the sunlight southern hemisphere becomes less direct, the solar radiation and ■ The spring equinox—spring in the north- the heat it produces are proportionally less ern hemisphere, autumn in the southern intense. So it is warmer in the tropics and hemisphere, when sunlight is again most colder at the poles. In between regions direct at the Equator experience more seasonal variations.
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Likewise, depending on the time of day the Mercury Axial Tilt is 0º and There is No angle of sunlight changes as the world turns: Atmosphere to Distribute Solar Radiation at midday, when the Sun appears highest in Similarly, Mercury’s the sky, we receive the most direct sunlight, axis of rotation is and that is usually the warmest part of the oriented nearly day. Sunlight is less direct in the morning and perpendicular to its evening, also usually cooler times of day. orbit, so that in the polar regions sunlight Moon’s Axial Tilt is 1.5º and There is No strikes the surface at Atmosphere to Distribute Solar Radiation a constant grazing Although the plane of the Moon’s orbit angle. Its poles have around the Earth is inclined about 5º, it’s been pointing in the equator is inclined about 6.5º, resulting in same direction ever a 1.5º tilt of the Moon’s spin axis to the since the planet was formed. orbital plane around the Sun. This means that sunlight always just grazes the poles of The interiors of large craters at the poles the Moon. Some craters in the lunar polar are permanently shadowed and remain regions are permanently in the shadows and perpetually cold, below -350° F (60 K). never receive any sunlight. At temperatures Below 80 K, the molecular motion of ice of 40 to 50 Kelvin, craters could act as “cold is nearly nonexistent. Ice is stable at that traps” that could keep ice so solidly frozen temperature even in a near vacuum and that almost none of it escapes into space. does not sublimate as vapor into space. Possibly, the tiny influx of ice from infalling comets and meteorites could be cold-trapped in these Mercurian polar caps over billions PRINT of years. Or water vapor might originate from the planet’s interior and be frozen out at the poles. Alternatively, it has been suggested that the polar caps consist of a different material, perhaps sulfur sublimated over the eons from minerals in the surface rocks.
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So which is it? How can water ice be cold- Recapping the Evidence trapped in craters of polar regions even on In 1994, the Clementine mission confirmed small worlds, even close to the Sun, such that conditions for a cold trap that could as Mercury and the Moon? support lunar ice existed by bouncing radar and receiving highly reflective signals, Hmmm, How Could the Ice Get There? indicating the likely presence of ice. In Is there water that outgasses from the planet’s 1999, the Lunar Prospector mission found interior that then freezes at the surface? somewhere between 10 to 300 million tons Could comets deliver ice? Such impacts of water ice scattered inside the craters might be so powerful (several megatons) of the lunar poles, based on data from its that any ice would be obliterated by the neutron spectrometer. energy of the impact, and could destroy Radar echo images of Mercury’s polar any ice that might already be there. regions, first obtained from ground-based Micrometeorite? Ice is traveling in radar telescopes at Arecibo in 1991, show abundance in interplanetary space. that the large craters’ interiors are highly Over billions of years, perhaps many reflective at radar wavelengths suggesting micrometeorite hits brought in the ice. the presence of ice.
How Could the Ice Stay There? We know that large craters in both polar After impact, ice molecules would hop around regions of Mercury and the Moon are: in the exosphere. Some might be lost over 1. C-c-c-cold, below -350º F (40– 60 K) time due to photodissociation, solar wind, 2. In perpetual shadow sputtering, and micrometeoroid gardening. Some jump straight out into space. 3. Highly reflective at the radar wavelength (an indicator of water ice) PRINT But some hop across the surface only to land and hop again, unable to escape the But to know for sure whether it’s ice or Moon’s or Mercury’s gravitational field. hydrogen sulfide we need new data: These molecules continue to move around ■ High flux of low-energy thermal in a process aptly called, a ‘random walk’, neutrons—indicates hydrogen (H) slowing down as they jump into cooler ■ Ultraviolet and gamma ray detectors— areas until they reach an area that is below indicates sulfur or oxygen 80 degrees Kelvin (80 K). Once inside these ‘cold traps’, the molecules are so cold they stop hopping altogether and could lie trapped for billions of years.
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Cosmic Rays and a Cascade of slow down a great deal before hopping Neutrons and Gamma Rays into space. Meanwhile with each collision, It sounds like science fiction, but it’s true: the atoms get “excited” in the process, high-energy subatomic particles traveling and emit gamma rays to release the extra at nearly the speed of light, called cosmic energy so they can return to their normal rays, zip in from galaxies and stars (even rest state. Gamma rays are very short our own Sun) and rain onto planetary wavelength, high frequency, high-energy objects in the Solar System everyday. photons produced by a nucleus changing Where there is no atmosphere to filter quantum energy states, the shifting of the cosmic rays, they collide with atoms protons. It is light that is so energetic, it in the soil. When atoms are hit with such goes through most things, and would not energy, “fast” neutrons are released, even bounce back in a mirror. Gamma rays which scatter in all directions. Some jet have characteristic energy signatures for immediately into space, while others first each nucleus. So, by measuring the energy collide with other atoms. When neutrons of the emitted gammas, scientists can collide with relatively large atoms, they determine which nuclei are in a sample. only lose a little energy, and when they A clever combination of sensors can read jet out into space they are detected as the ratios of the different neutron energy medium-level, “epithermal” neutrons. levels and the signatures of the gamma But if they strike something their own rays. If the detector sees few or no size—such as an atom of hydrogen, they medium-energy neutrons, hydrogen must be present. Combined with data from other detectors, we can with confidence infer the presence of specific elements PRINT and their concentrations.
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Testing the Difference: Oxygen or Sulfur? Open Questions How can we tell whether the hydrogen On the Moon, the big question is whether is combined with oxygen as ice (H2O) or the ice is in big enough chunks that could combined with sulfur as hydrogen sulfide be used by human explorers. On Mercury, (H2S), a product of volcanic activity? the question is still to determine whether it is Different wavelengths of light are associated ice for sure. Once the MESSENGER Mission in different ways with the changing energy reaches Mercury and the Gamma Ray and states of elements of matter. Ultraviolet Neutron Spectrometer sends backs its data, light can reveal the signature presence of an we will have a more definitive understanding element such as sulfur. A gamma ray sensor of ice in its permanently shadowed craters. can detect the presence of oxygen.
[link to Ice on Earth]
[link to Ice Elsewhere]
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This table summarizes the Background Information
a. How do we detect ice on the Moon ■ Ice is inferred from readings of science [link to Magnified Ice] and Mercury? instruments that detect presence of hydrogen, such as Radar and Neutron Spectrometers. ■ Might NOT be ice—might be hydrogen combined with sulfur.
b. If it is ice, how did it get there? ■ Cometary and meteoritic impact ■ Water-rich asteroid impacts ■ Water vapor might originate from the planet’s interior and be frozen out at the poles.
c. How could the ice stay there? ■ Exists in perpetual shadow in cold traps colder than 80˚K.
d. How does a Gamma-Ray & Neutron ■ Gamma-Ray mode measures emissions Spectrometer work? from radioactive elements and gamma-ray fluorescence stimulated by cosmic rays; it’s used to map elemental abundances in crustal materials. Neutron Mode provides sensitivity to hydrogen in ices at Mercury’s poles.
e. How do we rule out that it might ■ Use an Ultra Violet Spectrometer PRINT not be ice? to double-check that hydrogen is not from a patch mixed with sulfur.
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ACT OUT THE SCIENCE Narration and Mime Activity: Movement Integration Mediating Experience The Story of Ice in the Shadows
Narrative Movement Concept There was once a polar Invite two or three students The dynamics of the polar region of a small spherical to play the polar region. regions of a planetary world just minding its own object such as Mercury or business. It was mainly a Have them stand together the Moon rocky outcropping that with arms outstretched. hardly ever got visitors. The light of the Sun only Identify a direction of the barely grazed the surface, room to be the sun and hurrying on by to the next invite some students to be planet. Every once in a while the “sunlight” passing by some particles from the and a “solar wind particle” solar wind zipped in and that kicks up some dust tossed up some exospheric dust. From the other direc- Invite a student from the Ice is traveling in abundance tion, micrometeorite dust other direction to enter in interplanetary space. Over particles hit the surface from as a “micrometeorite billions of years, perhaps time to time, kicking up a dust particle” many micrometeorite hits fuss and tilling the soil like brought in the ice. a garden; in fact, we call it The various particles hop micrometeorite gardening. about, back to their seats.
Occasionally things got A “comet” strikes the polar Such impacts might be exciting. Like when a comet region, in a slow motion so powerful (several mega- tumbled in toward the sun version of a major impact, tons) that any ice would be and struck the surface of the comet, “vaporizing” obliterated by the energy the world. That little world back to his or her seat. of the impact, and could PRINT would open its arms and destroy any ice that might catch that comet of ice, already be there. which would vaporize almost as quickly as it had crash landed.
But best of all was when a Invite several students Water-rich asteroid impacts. water-rich asteroid struck to become the water-rich just right and made a crater asteroid; upon impact, at the polar region, like a some become the cold burrow, so that the block trap, others are ice hop- of ice it carried came to pers who skitter and hop, rest there in the shadows, some skip right out into while scattering diamonds “space” escaping back of ice all around. to their seats…
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Narrative Movement Concept The scattered ice molecules More hopping about. Kinetic theory: the principles would hop around because of molecular motion. they have nothing else better to do, depending on how energetic or kinetically hot they are. Some hop right out into space, most hop and land somewhere else and then hop again.
Some take a “random walk” Identify a “crater space” hopping about until they where several ice hoppers find themselves down in the get “cold trapped” and crater with the big ice in a huddle together… “cold trap,” a place colder than 80º K—there they would stay huddled and frozen, hidden from view in the total darkness for billions of years.
The story could end right Telescopes and other there. We’d never know optical detectors depend about the place, because on the sun’s illumination no telescope or spacecraft to retrieve data. would ever see it because it was never illuminated by the sunlight, always hidden by the darkness.
Wait! Look! There! In the Invite a student to be a Cosmic rays are subatomic Sky! From a distant star cosmic ray source. particles from high energy in a distant galaxy! It’s a events traveling at near the PRINT cosmic ray, a particle travel- speed of light, from galaxies, ing nearly at the speed of stars, or the Sun. light zipping in toward the polar region!
Stop the Action! Freeze!
If that cosmic ray strikes Explain, foreshadows next near the ice in the shadows, action… where it’s been cold trapped for billions of years, we might be able to be at just the right place at the right time to measure its cascading effect.
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Narrative Movement Concept We need to position a Create a spacecraft with spacecraft with a Gamma two spectrometers. Ray and Neutron Spectro- meter and an Ultraviolet Spectrometer to boot.
Here we are. Ready. Ultra Let the cosmic ray strike! slow motion.
As cosmic rays strike the Transform some ice When neutrons collide nuclei of atoms on the hoppers into fast with relatively large atoms, surface, they knock loose neutrons escaping. they only lose a little energy, fast neutrons: some move and when they jet out into fast enough to escape the space they are detected as planet directly. medium-level, “epithermal” neutrons.
Other, slower neutrons Transform other ice hop- But if they strike something strike ultra frozen nuclei pers into neutrons escaping their own size—such as just their own size— like getting slowed down by an atom of hydrogen, they hydrogen! Those neutrons the presence of ice… slow down a great deal then move really slowly, before hopping into space. and hop out into space.
The neutron sensor on the Hopping into space, the It detects neutrons in three spacecraft can measure how “neutrons” get detected, energy bands: fast, those fast the neutrons are going— counted by the spacecraft that were loosened with the and an absence of medium sensors. cosmic ray burst immedi- neutrons and enough slow ately; epithermal, on their ones means a patch of hydro- way to being slowed down; gen has been detected! But thermal, slowed down, wait- what was that hydrogen ing to be absorbed in the combined with? Oxygen to regolith (and a signature of make ice? Or Sulfur to make the presence of hydrogen). PRINT hydrogen sulfide?
As they move out, gamma A student releases a gamma Gamma rays have charac- rays, high-energy photons ray (with rapidly waving teristic energy signatures of nuclear light, are also arms) with O signature for each nucleus. So, by released with a detectable and gets detected. measuring the energy of signature of the neighboring the emitted gammas, scien- atoms—the gamma ray tists can determine which sensor can tell whether it nuclei are in a sample. was—“oxygen!” and the Ultraviolet sensor checks for sulfur.
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Narrative Movement Concept Ice in the Shadows? Or not Everyone pose dramatically. Ice? That is the question.
Either way, whatever the Return the focus to the polar Future missions such actual results, we learn region, the cold-trapped ice, as MESSENGER, Bepi- more about how the Solar the spacecraft, as this closing Colombo and new efforts System has evolved. By thought is spoken. to explore the Moon will looking at the polar region answer these compelling in several ways, we get questions. the whole picture!
Small Group Mime Activity: Movement their own mime and narrated story about Integration Mediating Experience how ice may have gotten there. Encourage Invite students to form small groups (about students to act out a sequence that results in three to five students), look at images of the drawing science questions from the story. features on Mercury and the Moon and create
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MATERIALS DEMONSTRATION For All Activities, to Record Reflections, The purpose here is to help young children Observations, Calculations, etc. relate the notion of how a more direct Science Notebooks: writing and or less direct angle of sunlight can make drawing utensils. a difference. Demonstration The angle of the sunlight hitting a planet is different at different locations because a planet ■ Musical Horn is spherical. The angle makes a difference in ■ Electric or battery-operated fan the heat generated at the surface. Consider Warm Up Activity different ways of showing a difference in effect ■ Two 5-10 lb. chunks of ice between more direct and less direct angles. ■ Globe of the Earth Main Activity ■ Hair dryer or heat lamp ■ Ice cubes ■ Modeling Clay ■ Toothpicks Ice in the Shadowed Craters ■ Gallery with NASA images of Mercury and the Moon (See Resources)
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PRE K–2 3–5 The Analogy of Sound The Analogy of a Fan Does the directness of the angle between Does the directness of the angle between you and the source of the sound make a you and the source of the breeze make a difference in how well you hear it? difference in how well you feel it? Invite a student to come up to the front. Have Invite a student to come up to the front. in hand a simple musical horn or noisemaker. Have at hand a movable electric fan. Ask Ask the student to practice making a contin- the student to practice controlling the uous sound with it. Now instruct the child direction of the fan in a continuous smooth to start by facing away from the class. Start motion. Now instruct the student to start blowing the horn and slowly turn around in by facing away from the class. Start the a full circle, turning toward and then away fan blowing and slowly turn around in a from the class. full circle, turning toward the class and Lead a discussion about what students then away again. observed about the loudness of the sound. Lead a discussion about what students Why is the loudness different at different observed about the intensity of the breeze. angles? At what position did it sound the At what position did it seem the breeziest? loudest? When the horn is blowing straight When the breeze is blowing straight at you, at you, is it the loudest? Is it as loud when is it the most intense? Is it as strong when it is at a glancing angle or when it is pointed it is at a glancing angle or when it is pointed away from you altogether? away from you altogether? Repeat the demonstration several times. Repeat the demonstration several times. Point out the different angles involved. Point out the different angles involved. PRINT Connect this experience to the main activity: Lead a discussion about why students think drawing upon the experience with the it feels different at different angles. sound to explain how sunlight is “loudest” when it strikes more directly at the Equator Connect this experience to the main and “quieter” when it strikes indirectly at activity: drawing upon the experience with the poles. the fan to explain how sunlight is “breezier” when it beams more directly at the Equator and less “breezy” when it beams at a grazing angle at the poles.
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MAIN ACTIVITY This activity involves modeling the effect Diagnose of the angle of sunlight on a planet and Listen to student ideas about the spherical connecting to ice on polar regions. shape of the Earth, the Moon, and Mercury. How well do students grasp the change in PREPARATION the angle of sunlight due to the curvature? ■ Devise exploratory zones for small groups Listen to student ideas about the implications to construct spheres of modeling clay and of being at different places on the globe. to embed ice cubes. What knowledge do the students bring in to the table as they examine the information ■ Devise exploratory zones to look at polar regions of the Moon and Mercury, using about how ice may form in permanently NASA images. shadowed craters at the poles of Mercury and the Moon? Do they connect the dots?
TEACHING TIPS Design Explore Have students work in collaborative teams These exploratory zones aim at making the to research questions that arise from the complexity of spherical geometry simple visits to the exploratory zones, especially and direct. Best not to rush the students drawing comparisons between their controls toward premature closure. A lot of mental and variables. Have students design a mission gymnastics are involved to visualize how to with astronauts that would accomplish the translate our experience of standing on the exploration of ice on the Moon. Earth to a projection of our position on the spherical Earth and the curvature in relation Discuss to the incoming sunlight. Allow students How do scientists learn about places like to repeat the steps several times as they Mercury and the Moon? Observation of places PRINT encounter the phenomenon and model it. like Mercury and the Moon is technologically challenging. What are the big questions scien- tists are asking? Explore how students view a new era of lunar exploration.
Use This activity connects concepts about detecting ice with a gamma ray and neutron spectrometer. Invite students to explore how this technology is used on Earth to detect things of interest. How does this exploration relate to other concepts about the Solar System?
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WARM-UP AND PRE-ASSESSMENT Point out that a sphere presents different A day or so before the main activity set out angles due to its curvature. Illustrate this two big chunks of ice (5 or 10-lb chunks), explicitly by using a modeling clay sphere one in the direct sunlight and one in indirect and placing toothpicks to show that this is sunlight, in the shade. Ask students to predict why the angle of sunlight changes as you which chunk of ice will melt faster and then move from the Equator toward either pole. to observe and propose an explanation. Go on to point out that the Moon and Just before the main activity, lead a discus- Mercury are also spherical, but are not sion about their predictions, observations significantly tilted with respect to the Sun. and proposed explanations. With this is mind, but without seeking Then invite the students to briefly examine an answer at this moment, ask students the spherical features of the Earth: Examine to discuss the question: Where on these a globe of the Earth. Guide students to worlds would a chunk of ice melt faster and notice explicitly that the Earth is spherical where would it melt slower or not at all? and tilted at an angle with respect to the (See discussion and reflection) Sun. Manipulate the globe in such a way as to guide students to notice the area of the Earth that receives the most direct sunlight is bounded by the Tropic of Cancer and the Tropic of Capricorn. The North and South Poles are at the top and bottom of the world where the sun shines at a grazing angle.
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PROCEDURES PART 1. Have each student scratch a line to mark the Modeling the Sphericity of Mercury Equator, where the Sun shines most directly; and the Moon and to mark the north and south poles, the Have each student make a spherical “top” and “bottom” of Mercury or the “Mercury” or “Moon” out of modeling Moon, where the Sun shines least directly. clay.Have students notice the different Optional: Make the spheres and position angles in relation to the “Sun,” explicitly, them accordingly and then cool the clay by having them place toothpicks straight prior to the ice melting experiment. in and noticing that they point out in different directions (angles).
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PART 2. Ask students: Which ice cube is likely to Do Angles Make a Difference? melt faster? Have students work as partners, with Have students switch roles and repeat: [link to: Act It Out two modeling clay worlds (a control and a Using one “world” as a control, do nothing. Final.2005.pdf] variable). Have one student be ready with Toward the other, aim the heat source in the heat source (hair dryer or heat lamp) such a way as to create warm air blowing to aim directly toward the Equator of the toward it. Make sure the air current reaches variable world. (This represents the thermal the whole sphere from one direction. effect of solar radiation.) The “equatorial ice” receives a more direct The control sphere is off to the side to angle of warmth. The “polar ice” receives a account for any effect of room temperature less direct angle of warmth. Also, see what and the warmth of the clay itself. happens if the ice cube sits in a “crater” Once the heat source is in position, ready near the pole. to be turned on, embed ice cubes in model- Be sure to compare the variable to the ing clay spheres, at 90º apart, representing control. Because we are in a classroom on an equatorial and a polar region. Push each Earth and not in a laboratory or in space, the ice cube in far enough so that it’s top surface ice on the control is also melting. If the ice matches or sits below the clay surface. melts more rapidly with the hair dryer, can we Turn on the heat source and aim it directly infer that the hair dryer made the difference? at the Equator of the variable world. Does melting occur differently at different Notice the effect on the ice cubes. Observe angles (that is, does a direct equatorial angle and time how quickly the ice cubes melt. melt the ice more readily than the warmth Write and illustrate new understandings that moving over the top? What happens where PRINT result from this activity. you created a “crater,” where the warmth rides over it altogether?
Polar region
Equatorial Region
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What happens? Control World Variable World
Ice Cube at Equator
Ice Cube at the Pole
Optional: Invite students to examine the situation in greater depth. Subtracting the melting of the control world from the melting of the variable world might reveal that virtually no melting occurs due to the heat source when the ice cube is embedded in a shadowed crater. That is, if you could establish that the melting of the control and the variable at the pole is the same, then you can infer that the heat source had no effect because the heat did not reach the ice, just as ice in the permanently shadowed craters of Mercury and the Moon can only remain stable if NO sunlight ever reaches it.
This Table Connects the Model to the Phenomenon to guide discussion
Precursor Concept Mercury and Moon Connection
Ice melts faster in direct sunlight than in Ice melts or sublimates rapidly in direct the shade. sunlight; slowly in indirect light. Compare angles with modeling clay Aimed at communicating that that a worlds and toothpicks, in relation to sphere presents different angles to a reference point. a reference point (the Sun). PRINT Ice cube placed at equatorial region melts Directness of sunlight at equatorial regions faster than ice cube placed at polar region. versus grazing angle at the polar regions. Ice cube at pole in variable world shows Any ice that receives sunlight would almost no difference in melting compared sublimate very rapidly, evaporating to ice cube at pole in control world. into space; For ice to exist on an inner planetary world, it must be permanently shadowed in craters that craters allow NO sunlight or heat.
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PART 3. part of a year, it would raise the temperature Gallery of Moon and Mercury Images enough for the ice to shiver and hop free Have students look at a gallery of images into space. So, wherever sunlight strikes of the polar regions of Mercury and the directly, the temperature goes way up, the Moon. Ask students to relate the activity ice would disappear fast, sublimating and they just completed to the exploration of melting away. Only in places that NEVER get Mercury and the Moon. Have students ask sunlight or its warmth—permanently shad- questions and pose explanations about owed craters and underground in the polar what they noticed. regions can ice remain stable.
DISCUSSION & REFLECTION How is a Gamma Ray and Where On These Worlds Would a Chunk Neutron Spectrometer Part of Ice Melt Faster and Where Would It of Everyday Experience? Melt Slower or Not At All? Have you ever traveled by air? Then Scientists were surprised that ice exists gamma ray and neutron spectrometers in the shadowed craters of Mercury and are part of your experience. If you have the Moon. In the near vacuum conditions traveled, then your baggage has been of the exosphere, with the vapor pressure scanned at airport security checkpoints. at zero, over time, ice molecules at the Gamma ray and neutron spectrometers surface would be expected to sublimate, are not only used for space exploration, to hop off going directly from solid to they can detect combinations of elements vapor. The only explanation is that in these that are typical of explosives. They are most useful in detecting traces of radioac- regions, it is sooooooo c-c-c-cold that the tivity and have been used to inspect for ice molecules are way beyond shivering— weapons of mass destruction. PRINT they stop moving altogether and just stay there, huddled together for billions of years. If sunlight were to strike the cold trap directly or indirectly even for a small
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And What About Those Cosmic Rays? The most important realization is in Just how amazing does it seem to you that understanding how the angle of incidence a particle flying in from another galaxy can of light from the sun differs, not because help us find ice hidden in the shadows of the angle from the Sun is changing, but Mercury and the Moon? that the curvature of the spherical Earth changes as you move north or south from CURRICULUM CONNECTIONS the middle regions—so it depends on This lesson challenges the students to your position at a given time of day and think about the geometry of spheres and time of year. Mercury and the Moon are to project that thinking to what it means slightly simpler systems because their tilt is to be standing on a slightly tilted, spinning negligible—but they are both still spherical. sphere. This lesson connects to geometry Students are asked to comprehend the and thinking about angles. connection between the world, and the K–5 students are expected to be able way we represent it in textbooks, draw- to analyze characteristics and properties ings, and models. This activity creates an of two- and three-dimensional geometric opportunity for students to apprehend a shapes and develop mathematical spherical object in this context. arguments about geometric relationships. This activity also lays the groundwork for This lesson provides direct experience precursor understanding of fundamental with three-dimensional spheres and the phenomena such as why the seasons opportunity to wrestle with geometry. change the way they do.
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ASSESSMENT CRITERIA Exemplary Emerging ■ Students write and illustrate new ■ Students write and illustrate a descrip- understandings that result from the tion of the conditions of ice on Earth, exploratory zones and share it with Mercury and the Moon, sharing ideas both a small group and the whole group. with a small group and the whole group.
■ Students display drawings, construc- ■ Students pose basic science questions tions, and dynamic models drawn drawn from their observations and from their science notebooks and research about ice in the shadows. web-based research. ■ Students observe images and data ■ Students identify and extend science about ice on Mercury and the Moon. questions drawn from research about ■ Student display results using a variety ice in the shadows. of ways to represent examples of ice ■ Students ask a rich and extensive range on Mercury and the Moon. of questions about ice on Mercury and ■ Students ask a rich range of questions the Moon: micrometeorite gardening, about the origin, structure and cratering, and the exosphere. composition of polar ice on Mercury ■ Students extend learning by considering and the Moon. implications of the view that ice may ■ Students make speculations about reside in “cold traps” in craters at the possible explanations for ice on poles of Mercury and the Moon. Mercury and the Moon.
■ Students relate ideas to whole context Formative of exploring ice in the Solar System. ■ Students recognize places in the inner PRINT Solar System where polar ice has been detected: Mercury and the Moon.
■ Students pose science questions about ice on Mercury and the Moon and why the angle of sunlight makes a difference.
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RESOURCES Mercury Moon http://nssdc.gsfc.nasa.gov/planetary/ice/ http://www.psrd.hawaii.edu/Dec96/ ice_mercury.html IceonMoon.html Ice on Mercury Ice on the Bone Dry Moon Written by Paul D. Spudis http://messenger.jhuapl.edu Deputy Leader of the MESSENGER Mission site Clementine Science Team http://nssdc.gsfc.nasa.gov/planetary/ice/ http://lunar.arc.nasa.gov ice_mercury.html Lunar Prospector site, including discussions Ice on Mercury, discussion of evidence for of ice on the Moon and a relatively easy ice on Mercury to understand explanation of the neutron spectrometer
http://nssdc.gsfc.nasa.gov/planetary/ice/ ice_moon.html Ice on the Moon, discussion of Lunar Prospector results
Images Link to image gallery
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