1. Equipping the Next Generation for Active Engagement in Science
Life on Enceladus?

2. A billion miles from the Sun a tiny moon, Enceladus, orbits Saturn.
Enceladus is one of the brightest objects in the solar system.
Ask pairs to speculate on reasons for the moon’s brightness. Take feedback.
shadow of Enceladus
other moons − Tethys, Dione, and Rhea 2
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3. Is this true? Where could the liquid water be?
Enceladus is covered in clean white ice.
Its surface temperature is −200 ºC.
Yet scientists say it has oceans of hot liquid water.
Point out that Enceladus’ icy surface reflects 99% of the light from the Sun that reaches it. This is the reason for its brightness.
Elicit the melting point of water on Earth (0 ºC) and ask students to suggest where the liquid water might be on Enceladus.
Check that students know the difference in particle arrangements in a typical substance in its solid and liquid states.
Is this true? Where could the liquid water be? 3
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4. If Enceladus has oceans, could it be home to alien life?
On Earth, life may have started in the oceans.
Lava, hot water and sulfur compounds burst into the ocean from seafloor hydrothermal vents.
Chemical reactions around these vents formed the molecules of the first living things.
This slide introduces one theory of the origin of life on Earth. Might there be similar undersea vents on Enceladus? Might this moon harbour alien life?
If Enceladus has oceans, could it be home to alien life? 4
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5. In this activity, you will
Decide whether the evidence supports the conclusion that there is hot liquid water on Enceladus:
Matter: How particle arrangements explain the properties of liquid water and ice
Consider conclusions: Assess the strength of evidence for a conclusion
Big Idea
Working Scientifically

6. Scientists have made two conclusions:
1 There is hot liquid water on Enceladus
2 Enceladus could be home to alien life.
Does the evidence support the first conclusion?
robot spacecraft Cassini
Tell students about Cassini, a robot spacecraft which has, since 2004, been sending a daily stream of data collected by its twelve instruments from Saturn’s system.
The slide gives two conclusions that scientists have made from this data.
If so, is it worth sending another spacecraft to look for alien life? 6
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7. SS1-2
Does the evidence support the conclusion that there is hot liquid water on Enceladus?
1 Read the evidence cards and look at the images.
2 For each evidence card:
Decide which box on SS2 you think it should go in.
Write the title of the evidence card in this box.
3 In your group, weigh up all the evidence and decide on an answer to the question above.
4 Work alone to write down your own answer to the question above. Explain your decision.
Student groups study the evidence cards around the room (SS1a – h) and decide whether each piece of evidence is strong or weak evidence for or against the conclusion that there is hot water on Enceladus. They write the title of each evidence card in one box on slide SS2.
Suggested answers are:
Evidence for the conclusion – A, B, C, E, F, H
Evidence against the conclusion – D, G
Student groups then tackle task 3 (7). There is no one correct answer – it is up to students to weigh up the evidence for themselves.
Individual students tackle task 4 (7) to allow for the assessment of individual learning.
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8. What else do you want to know before you decide?
SS1-2
Is it worth sending a spacecraft to look for alien life?
Display (8). Student groups, or the class as a whole, discuss whether it is worth sending a further spacecraft to land on Enceladus to look for evidence of alien life.
Further questions will arise during this discussion, for example What are the benefits of finding out if there is life on Enceladus? What are the costs of sending a spacecraft to this moon? When might data from the spacecraft enable scientists to answer the question?
What else do you want to know before you decide?
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9. Life on Enceladus? Student sheets Sheet no. Title Notes SS1a – h
Evidence cards
Reusable, print one or two copies of each in colour to display on the classroom wall.
SS2
Organising evidence
Reusable. One per group.

10. Evidence card A ICE Geysers
SS1a
Evidence card A
Geysers
Cassini detected more than100 geysers erupting from cracks in the surface of Enceladus.
The geysers blow out 200 kg of water every second, as water vapour and tiny ice crystals.
Water vapour and tiny ice crystals
ICE
Some scientists think that the source of water for the geysers may be a buried sea of liquid water.
Print and display on the wall.

11. So any liquid water on Enceladus is probably under the ice.
SS1b
Evidence card B
Solid and liquid
Particles in solid water (ice)
Most substances have a higher density as a solid than as a liquid. This is because particles are more closely packed in the solid.
But water is different. At 0 °C particles are more closely packed in the liquid. This means that liquid water has a higher density than ice.
Print and display on the wall.
So any liquid water on Enceladus is probably under the ice.
Particles in liquid water

12. Evidence card C Gravity
SS1c
Evidence card C
Gravity
As Cassini flew past Enceladus, it changed direction. Scientists monitored the change of direction. They said it was caused by the gravitational field of Enceladus.
Scientists calculated that Enceladus has more mass at its south pole than you would expect if the moon was ice all the way down to its rocky core.
Print and display on the wall.
Liquid water at 0 °C has a greater density than ice, and so more mass for a given volume. An ocean under the ice could explain the extra mass at the south pole.
liquid water
ice
rocky core

13. Cassini has not detected these new substances in the geysers.
SS1d
Evidence card D
Cyanide
geysers
Cassini observed samples of the mixture that comes out of the geysers on Enceladus.
mass spectrometer
An instrument called a mass spectrometer identified one substance in the mixture as hydrogen cyanide.
Hydrogen cyanide reacts with other substances dissolved in liquid water to make new ones.
Print and display on the wall.
Cassini has not detected these new substances in the geysers.

14. Much of the sand on Earth is silicon dioxide.
SS1e
Evidence card E
Rocky grains
Cassini took samples of substances that come out of the geysers on Enceladus.
The mixture includes tiny grains of rock. The rock is mainly silicon dioxide.
Scientists suggest that the rock grains form like this:
Hot water moves upwards. It contains dissolved substances from the rocky core. The concentrated solution is slightly alkaline.
The hot solution comes into contact with cold water. It cools quickly.
Tiny rock grains come out of solution.
Print and display on the wall.
Much of the sand on Earth is silicon dioxide.

15. This could create underground seas of liquid water.
SS1f
Evidence card F
Hot core
Cassini measured the temperature at the south pole of Enceladus as −116 ºC. This is warmer than the temperature of other bodies at the same distance from the Sun.
Scientists suggest that the high temperature is evidence that Enceladus’ has a hot core.
Energy from the core might raise the temperature enough to melt some of the ice under the south pole.
Print and display on the wall.
This could create underground seas of liquid water.

16. This picture shows solid carbon dioxide subliming.
SS1g
Evidence card G
Sublimation
Geysers erupt from Enceladus. The geysers give out water vapour and tiny ice crystals.
Sublimation is the change from the solid state to the gas state, without going through the liquid state.
Print and display on the wall.
Some scientists say that the water vapour forms when ice under the surface sublimes.
This picture shows solid carbon dioxide subliming.

17. The surface of Enceladus is not smooth.
SS1h
Evidence card H
Surface
Some areas of Enceladus have big craters in its surface.
The surface of Enceladus is not smooth.
Other areas have no craters. Scientists say that this is evidence that the surface recently changed.
Print and display on the wall.
The different features on the surface of Enceladus suggest that it may have been active with water volcanoes which have changed its surface over time.

18. Organising evidence Conclusion There is liquid water on Enceladus.
SS2
Organising evidence
Conclusion There is liquid water on Enceladus.
Strong evidence for the conclusion
Strong evidence against the conclusion
Student groups record the names of each evidence card in one box on this sheet, according to their judgement of each piece of evidence.
Weak evidence for the conclusion
Weak evidence against the conclusion

19. Credits Picture Slide Credit Saturn with moons 1
Goddard Space Flight Center, NASA
Surface of Enceladus 2
NASA
Sully main endeavour field 4
National Oceanic and Atmospheric Administration
Geysers on Enceladus
SS1a
Water molecules in ice and liquid water
SS1b
Wikimedia commons – picture created by Ascalaph Designer program
Cut-away diagram of Enceladus
SS1c
Space Science Institute, Jet Propulsion Laboratory, NASA
Cassini spacecraft
SS1d
Jet Propulsion Laboratory, NASA
SS1e
Hot core of Enceladus
SS1f
Sublimation
SS1g
Wikimedia commons
SS1h

20. Get students talking and thinking

21. Equipping the Next Generation for Active Engagement in Science
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