Astrobiology in the Classroom
NASA – CERES
Project –http://btc.montana.edu/ceres
“Remote Sensing - What we
can learn when we can’t touch?”
As we search for life in the universe it has
become essential that we are able to identify the chemical composition of planets
and moons both inside and outside our solar system. Remote sensing is one of the most valuable tools that
scientists use to gather information about the make-up of distant objects. In this lesson, students discover how
remote sensing is used to identify the signatures of life even when the
particular life form is not directly observable. Students begin by investigating how a satellite
“sees” objects on the surface of Earth and, in turn, students learn
the concepts of reflected and absorbed visible light. In the next activity, students learn about infrared light
and how it is related to the temperature of an object and the emission of
light. Finally, students explore
the concept of spectra and false color images while examining remote sensing
images of Earth, Mars and Titan in a search for the signatures of life in the
solar system.
Remote
Sensing - What we can learn when we can’t touch?
Introduction
Astrobiology is the science that searches for evidence of life in the universe. Often this research involves the study of objects that cannot be touched or even seen directly. To do this we typically look for clues that signal the presence or behavior of objects that cannot be directly observed.
As an example of this from everyday life, imagine that it’s your birthday, and your Aunt Patty has just given you a brightly wrapped present. What’s in the package? How can you find out without opening it? You might first be able to determine what it is not by its size. Suppose it’s too small to be a bicycle and probably too big to be watch. Next you could pick it up. Is it heavy or light? You could shake it. Does it make a sound? Is the sound a rattle or a thud? Next you could remove the wrapping paper. Are there markings on the box that give away what it is? Open the box, but before you look inside put in your hand and feel around. Do you feel tissue paper? Is the object hard or soft? Can you tell if it’s made of metal, wood, plastic or fabric? You could smell it. Does its smell help you figure out what it is? Now look at it. Pull it out of the box. Turn it over, take it apart and put it back together. Hopefully it’s just what you wanted.
There are many ways we learn about the world around us. We use all of our senses – sight, hearing, touch, smell, and taste. Scientist use all of their senses too. In fact they build instruments that help their senses gather information. They might use a magnifying glass or microscope to look at something very small in order to see more detail. Astronomers use a telescope to look at things very far away. Chemists have developed instruments that help them “smell” minute quantities of a material in a mixture that they might not be able to detect with their nose or that are to dangerous to inhale directly.
When scientists want to study
things that they can’t touch, take apart or have direct contact with,
they often make observations using the technique called Remote Sensing. With
remote sensing, information about an object is gathered from a distance without
ever touching or possibly even directly seeing the object.
Part I –
Exploration: What can our senses
tell us?
Activity
#1 Seeing the Wind
In this activity we will investigate the phenomenon we call “the wind” in an effort to understand the process of remote sensing.
A. As a group write a brief answer for each of the following questions.
What is the wind made
of?
Does the wind have a speed
and direction?
What color is the wind?
What is wind chill?
B. Which of the questions from part A can you answer best using
the techniques of remote sensing?
Think of how you could get the necessary data using your eyes or other
test equipment without ever having direct contact with the wind. Explain your reasoning.
Part II – Concept Introduction: Seeing the Light.
Activity #2 Seeing like your eye.
In
the figure below a satellite is used to gather images of the Earth’s
surface. This satellite, like your
eye, is sensitive only to visible light.
Although the sun gives off many other types of light we will be
concerned with only the visible light (including all the colors of the rainbow)
given off by the sun.
A. Would the different objects all look the same to the satellite? What is different about the objects?
B. Describe the path that the light takes after it leaves the sun.
C. What color will the satellite detect from the trees?
D. Which color(s) of light reach the trees from the sun?
E. Which color(s) of light are sent from the trees to the satellite? Explain how you know.
F. Where do the remaining colors of light that were sent by the sun go once they reach the trees? Explain your reasoning.
G. Explain why the roof of the house appears red to the satellite?
H. Would the satellite still detect the roof of the house to be red late at night, long after the sun had set? Explain your reasoning.
Scientist use the word reflected to describe light that hits the surface of an object and then bounces off the object. They use the term absorbed to describe light that hits the surface of an object and then enters the object.
I. In the drawing on the previous page label the light rays that are being reflected with the appropriate color of light.
J. To make the drawing above complete, what additional information would need to be added?
K. Use the terms reflected and absorbed to describe how the satellite detects the trees as being green?
Activity
#3 Where is the light coming from?
At
right is a picture of the sun, a yellow lamp, and a red apple. The lamp is turned off (Case 1.)
A. Would you be able to see the apple? If so, what color is it?
Explain why it is visible to your eye. In particular, describe the path that light takes that allows you to see the apple.
B. Would you be able to see the lamp? If so, what color is it?
Explain why it is visible to your eye. In particular, describe the path that light takes that allows you to see the lamp.
Now imagine that the lamp is turned on (Case 2.)
C. Would you still see the apple? Would it look the same as it did in Case 1? Is it the same color? Is it in the same position? Is it the same brightness?
D. Would you still see the lamp? Would it look the same as it did in Case 1? Describe how the lamp might look different from Case 1, if it does.
E. Is all of the light you see coming from the apple in Case 2 reflected light? Explain.
F. Is all of the light you see coming from the lamp in Case 2 reflected light? Explain.
G. Is all of the light you see coming from the lamp in Case 1 reflected light? Explain.
When light is generated from within an object and given off, we call this light emitted light. We now have three terms to describe the behavior of light: reflected, absorbed, and emitted.
H. For Case 1, list which objects are emitting light, which are reflecting light, and which are absorbing light.
emitting reflecting absorbing
I. For Case 2, list which objects are emitting light, which are reflecting light, and which are absorbing light.
emitting reflecting absorbing
Activity
#4 How hot does your potato look?
Your Mom bought two identical potatoes at the store. She put one potato in a cold freezer, and the other potato in a warm oven. Some time later she took the potatoes out of the freezer and the oven and placed them down on the table.
A. Could you tell which potato is cold and which one is hot by just looking at them? Explain how or why not.
B. Could you tell which potato is cold and which one is hot if you were to hold them in your hands? Explain how or why not.
Now imagine that you could not get close enough to the potatoes to hold them, but still wanted to determine which was hot and which was cold. This is the type of problem that is encountered when one does remote sensing.
Consider the two pictures shown below. Picture 1 comes from a camera that is sensitive to visible light like our eye. Picture 2 comes from a camera that is sensitive to only infrared light (not visible light.) Scientists look at the infrared light emitted by an object because this form of emitted light is closely related to the temperature of the object. In a typical infrared picture, objects that appear bright are at higher temperatures and objects that appear dark are at colder temperatures.
Picture 1: Taken with camera sensitive to only visible light.
Picture 2: Taken with camera sensitive to only infrared light
C. For Picture 1, is the light coming to the camera reflected or emitted light? Is it visible or infrared? Explain your reasoning.
D. For Picture 2, is the light coming to the camera reflected or emitted light? Is it visible or infrared? Explain your reasoning.
E. Which potato is hot? Which potato is cold? Explain your reasoning.
F. Describe a situation in which both of the potatoes would
be invisible to the human eye but not to an infrared camera.
G. Draw a sketch of what the infrared picture would look like the
next day after the potatoes were left on the table overnight.
H. Draw a picture that shows what the infrared camera would see
if it were pointed at a Styrofoam block and a metal block at the instant each
were removed from a freezer that they been left in a overnight.
I. Draw an overhead sketch (looking straight down) of
what the satellite in Activity #2 would detect if it were equipped with an
infrared camera.
Activity
#5 Where is the light coming from?
We have seen that when light
strikes an object some of the light is absorbed by the object and some of the
light is reflected off the object.
By sorting the different parts of light that are reflected off an
object, scientists are able to uncover the chemical composition of the
object. The drawing below shows
what the sorted light looks like.
This type of picture is called a line spectra.
Each line represents a different part of the light given off by the
object. Together the lines make up
a signature (like a finger print) that identifies the specific chemical
composition of the observed object.
A. Take a moment and study the different line spectra provided in
the Spectra Catalog. In the blank
box below sketch the line spectra that a satellite would detect if it were
pointed at a freshwater lake.
Explain the reasoning behind your choice of spectra.
Images of an object taken using
remote sensing devices often use different colors to represent specific
information about an observed object.
You may have seen an example of this when looking at a map or picture of
the Earth. Often mountain regions
are shown in brown while lowlands and valleys are shown in green. These colors do not represent the
actual color of the region but rather have been altered to illustrate the
elevation of the different areas.
An image that has had colors added to it, to represent specific
features, like elevation or temperature or chemical composition, is called a false
color image.
B.
Examine the
false color picture found at http://btc.montana.edu/ceres/astrobiology/RS/yellowstone1.jpg
This false color picture was
taken of the area around a geyser at Yellowstone National Park. The satellite that took the picture
used an instrument called a spectrometer to measure the spectra of different
chemicals and minerals in the surface around the geyser. The colors shown are not the actual
colors of the surface but rather have been used to identify where different
types minerals are present in the surface. In this image the reddish colored regions contain high concentrations
of the mineral hematite. The blue
colored areas contain high concentrations of the mineral calcium
carbonate. The white areas are
composed of primarily water and steam.
Sketch the different line spectra that
would have allowed scientist to make this false color image. With each spectra that you draw provide
a label of the corresponding chemical or mineral.
C.
Which
colored regions of this image do you think correspond most directly to the
location of the geyser? Explain
your reasoning.
On Earth there are specific
conditions and indicators that are used by scientists to identify the presence
of life. For instance, life as we
know it requires liquid water, and the majority of liquid water here on Earth
is found between the temperatures of 0 – 100o Celsius. Therefore, in our search for life in
the Solar System, we might look for signs that indicate that liquid water is
present or has been in the past.
Scientist have also identified chemical signatures for the presence of
life. For instance we might look
for the oxygen (O2), carbon dioxide (CO2), or methane (CH4)
that has been given off by living organisms.
D.
Examine the
false color picture found at http://btc.montana.edu/ceres/astrobiology/RS/yellowstone2.jpg
This black and white image was
taken of the same region of Yellowstone National Park now using an infrared
camera. Again the bright white
areas signify higher temperatures (100oC and above) and the darker
areas represent cooler temperatures (near 0oC).
Describe where you would look to
water (above 70oC).
Explain your reasoning.
E.
Examine the
false color picture found at http://btc.montana.edu/ceres/astrobiology/RS/yellowstone3.jpg
This false color image was taken
of another region of Yellowstone National Park. Again a spectrometer was used to measure the spectra of
different chemicals and minerals.
The turquoise colored areas
correspond to the spectra shown below.
The yellowish-orange colored areas
correspond to the spectra shown below.
The pinkish-purple colored areas
correspond to the spectra shown below.
Label
each spectra with the name of the corresponding chemical or mineral. Then identify a process or organism
that could have produced this chemical or mineral.
F. Imagine that the images from questions B, D and E were
remote sensing images taken by a satellite of a distant planet. Describe how each of the images could be used to support the
hypothesis that there is life on the distant planet.
Part III
– Concept Application: Do we
see the signs of life in our Solar System?
In
the following activities we will look at remote sensing images taken of other
planets and moons in our Solar System.
For each image, you should consider whether the information provided
suggests that life is or is not likely to occur on the planet or moon in the
image.
Activity
#6
Look
at the image found at http://btc.montana.edu/ceres/astrobiology/RS/Mars1.jpg
A. In this false color image of the planet Mars, what kind of
information is being displayed?
B. What is the range in values of the data?
C. What colors suggest that ice might be located on the surface
of Mars and in what region of the planet is it likely to be found?
D. Does the data provided in this image suggest that life could
exist on Mars? Explain your
reasoning.
Activity #7
Look
at the image found at http://btc.montana.edu/ceres/astrobiology/RS/Mars2.jpg.
This set of NASA Hubble Space Telescope images of the Martian surface include a true color image shown on the left and a false color image shown on the right. This true color image shows what Mars would look like to the human eye. The yellowish-pink color of the northern polar cap indicates the presence of small iron-bearing dust particles. These particles are covering or are suspended in the air above the blue-white water ice and carbon dioxide ice, which make up the polar cap. The false-color image highlights the distribution of different water-bearing minerals on the planet. The reddish regions in this image indicate areas of enhanced concentrations of water-bearing minerals. They are perhaps related to a water-rich history on this part of Mars. In particular, the large reddish region known as Mare Acidalium could have been a site of massive flooding early in Martian history.
A. Imagine that your research team is in charge of sending a lander to the planet Mars to search for signs that life either does exist or perhaps did exist at some time in the past. If you can only pick one landing site, where would you send your lander? Explain your reasoning.
B. Which of the line spectra from the Spectra Catalog do you think the Hubble Space Telescope could have detected when it was pointed at the reddish region shown in the false color image? List the names of each chemical or mineral and explain the reasoning behind your choices.
C. Based on the data presented in this image, and in the image from activity #6, do you think that it is likely that life exists on Mars now? What about in the past? Explain your reasoning.
Activity #8
Look
at the image found at http://btc.montana.edu/ceres/astrobiology/RS/IO1.tif
The image on the
right is a false color infrared image of the surface of the moon of Jupiter
called Io taken by the Galileo satellite.
For this false color image, a lighter color was used to indicate a
stronger emission of infrared light.
The comparison image on the left (from 1979 Voyager measurements) shows
the same view of Io as seen in visible light.
A. What information is the false-color infrared image telling us about the moon Io? Explain your reasoning.
B. Describe how the colors are used in the false color image to display the range of values for the feature that you identified in question A.
C. Which of the following possible features on the surface of Io are being identified by the labels in this infrared image: glaciers, hot spots and geysers, icebergs, volcanoes, or lakes? Explain your reasoning.
D. Do the features shown on the false color images appear to correspond with the image at left? Explain why or why not.
E. What does the information on the false color image suggest about the prospect for the existence of life on Io? Explain your reasoning.
Activity #9
Look
at the image found at http://btc.montana.edu/ceres/astrobiology/RS/IO2.tif
The image on the right is a false image of Io’s surface that was created using data from the on board spectrometer on the Galileo satellite. The comparison image on the left from 1979 Voyager measurements shows the same view of Io as seen in visible light. Sulfur dioxide (SO2), normally a gas at room temperature, is known to exist on Io's surface as a frost, condensing there from the hot gases emanating from the Io volcanoes and hot spots. The false-color image uses the colors white, shades of blue, and black to identify different concentration SO2 frost.
A. Sketch the line spectra that the Galileo satellite detected to make this false color image.
B. Compare this false color SO2 frost distribution image to the false color infrared image from activity #8. Identify the volcano Pele on the infrared image. Would you expect to find high or low concentrations of SO2 frost in the Pele region of Io? Explain your reasoning.
C. Which color of the SO2 frost distribution image do you think represents the highest concentration of SO2 frost? Which color do you think represents the lowest concentration? Explain your reasoning.
D. This false color image shows that the surface of Io has a large amount of SO2 frost. What does this data suggest about the prospect of life on Io?
Activity #10
Look
at the images found at http://btc.montana.edu/ceres/astrobiology/RS/Titan1.jpg
and http://btc.montana.edu/ceres/astrobiology/RS/Titan2.jpg,
then read the Titan information sheet found at the end of this lesson.
A. Which of the images Titan1 and Titan2 was
taken with visible light and which was taken with infrared light? Explain your reasoning.
B.
Which
spectra from the Spectra Catalog
do you think may have been used to produce the visible image? Draw and label the spectra below and
explain your reasoning.
C.
If the
bright region on the infrared image turns out to be an ocean, would this ocean
be the same as those found on Earth?
What chemical spectra would be seen if we were able to directly observe
this bright region in with visible light?
Explain your reasoning.
D. Based on the provided information, is it
likely that there is life on Titan?
Explain why or why not?
Activity
#11
As a group, create your own
remote sensing images (and corresponding spectra) to show what the results
might look like if you were to observe a planet that could support life. Explain the particular features of your
images and explain the reasoning behind your choices.
Spectra Catalog
Note: to see actual color
jpeg spectral line data of common elements used in astronomy go to:
http://home.achilles.net/~jtalbot/data/elements/index.html
1. Oxygen (O2)
Oxygen is a byproduct of photosynthesis, a metabolic process performed by the bacterium Cyanobacter. It is also produced by the photodissociation of water.
2. Carbon Dioxide (CO2)
Carbon dioxide is a byproduct of respiration, a metabolic process performed by the bacterium Escherichia coli. It is also released by volcanic outgassing. Carbon dioxide is found in the form of a gas or a solid.
3. Methane (CH4)
Methane is a byproduct of metabolism for bacteria such as Methanobacter. It is also formed in planeteary atmospheres as a result of photochemistry. Methane can be converted chemically into many other organic compounds.
4. Water (H2O)
Water can be found as a gas, solid, or liquid. It reacts readily with many minerals. It can be photodissociated into hydrogen and oxygen. In its liquid form, it is a solvent for bacterial life.
5. Hematite (Fe2O3)
Hematite is a mineral formed when oxygen reacts with an iron-rich rock in the presence of liquid water.
6. Sulfur Dioxide (SO2)
Sulfur dioxide is a gas at room temperatures here on earth but also settles as a frost on the surface of a planet that undergoes sulfuric volcanism. It is formed by chemically combining sufur and oxygen, a process that requires a temperature below 1000°C.
7. Calcium Carbonate (CaCO3)
Calcium Carbonate is a mineral that can be formed geologically, by water and carbon dioxide dissolving calcium and re-depositing it as a sedimentary rock. It can also be formed biologically, as plankton and diatoms form corals and seashells.
Titan Information Sheet
Discovered by: Christiaan Huygens, 1655
Distance from Saturn: 1,220,000 km
Radius: 2,580 km
Mass: 1.35 x 1023kg
Mean temperature at solid surface: 94 K (-178°C)
Major atmospheric constituents: nitrogen, methane
Saturn’s moon Titan was long thought to be the largest satellite in the Solar System, however, recent observations have shown that Titan's has a very thick, opaque atmosphere which hides its solid surface. Due to this extensive atmosphere the surface of Titan cannot be seen at all with visible light however some surface details are visible in the infrared.
Titan’s atmosphere has a surface pressure that is more than 1.5 bar (50% higher than Earth's). It is composed primarily of molecular nitrogen (as is Earth's) and methane. Interestingly, there are also trace amounts of at least a dozen other organic compounds (i.e. ethane, hydrogen cyanide, carbon dioxide) and water. The organics are formed as methane, which dominates Titan's upper atmosphere, and is destroyed by sunlight.
Observations have revealed that Titan is about half water ice and half rocky material. It is probably differentiated into several layers with a 3400 km rocky center surrounded by several layers composed of different crystal forms of ice. There is some speculation that its interior may still be hot. At the surface, Titan's temperature is about 94 K (-178°C). At this temperature water ice does not sublimate and thus there is little water vapor in the atmosphere.
It seems likely that ethane clouds may produce a rain of liquid ethane that falls onto the surface perhaps producing an "ocean" of ethane (or an ethane/methane mixture) up to 1000 meters deep.
Recent observations with the Hubble Space Telescope (HST) show remarkable infrared views of Titan's surface. Voyager's camera couldn't see through Titan's atmosphere but in the infrared the haze becomes more transparent, and HST's pictures suggest that a huge bright "continent" exists on the hemisphere of Titan that faces forward in its orbit. These Hubble results don't prove that liquid "seas" exist, however; only that Titan has large bright and dark regions on its surface. The landing site for the Huygens probe has been chosen in part by examining these images. It will be just "offshore" of the largest "continent.”